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Thermal performance of straw bales

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Thermal performance of straw bales

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O versize m aterials (e .g ., m aps, draw ings, charts) are reproduced by sectioning the o rig in a l, beginning a t th e upper left-hand com er and continuing from le ft to rig h t in equal sections w ith sm all overlaps. P hotographs included in th e o rig in a l m anuscript have been reproduced xerographically in th is copy. H igher quality 6" x 9* b la ck and w hite photographic p rin ts are a va ila ble fo r any photographs o r illu s tra tio n s appearing in th is copy fo r an a d ditio n al charge. C ontact UMI d irectly to o rd e r. P roQ uest Inform ation and Learning 300 N orth Zeeb R oad. Ann A rbor, M l 48106-1346 U SA 800-521-0600 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. THERMAL PERFORMANCE OF STRAW BALES by Nazneen Sabavala A Thesis Presented to th e FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In P artial F u lfillm en t o f th e Requirem ents fo r th e D egree MASTER OF SCIENCE (B U ILD IN G SCIENCE) August 2001 C opyright 2 0 01 Nazneen Sabavala Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 1409603 Copyright 2001 by Sabavala, Nazneen All rights reserved. _ _ ____ __ ( g > UMI UMI Microform 1409603 Copyright 2002 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UNIVERSITY OF SOUTHERN CALIFORNIA t h e g r a d u a t e s c h o o l U N IV E R S IT Y RARK LOS A N S C LE S . C A L IF O R N IA SOOOT This thesis, written by Ia z m e e n o a b a v a La under the direction of h £ & . Thesis Committee, and approved by all its members, has been pre~ sented to and accepted by the Dean of The Graduate School, in partial fulfillment of the requirements for the degree of ■ N 2>«sa Date. J . THESIS COM / Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS I would like to thank Professor Marc Schiler, head o f my Thesis Committee, fo r all his effort, tim e and patience in helping me to complete this thesis. I t would have been very d ifficu lt to complete it w ithout his guidance. I would also like to thank the other members o f my comm ittee, Professors Ralph Knowles and Pierre Koenig fo r th e ir tim e and availability. I express my sincere gratitude to CASBA (California Straw Building Association) for supporting me financially fo r this thesis. I t is great to know th a t CASBA supports even small- scale projects in their endeavor to further the knowledge o f strawbale in the building industry. Mrs. Dianne Schiler was absolutely wonderful in helping me to transport all my thesis m aterial. Finally, I would like to thank my friends for helping me during the entire experiment. Special thanks to Sreemathi Iyer, who was always available to help me whenever needed. Also a special thanks to Nazanin Zarkesh, who is a great driver! Thanks very much to all these people who were instrumental in the completion o f my experim ent Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS ACKNOWLEDGEMENTS................................................................................................... ii LIST OF FIGURES............................................................................................................vii LIST OF TABLES................................................................................................................xi ABSTRACT......................................................................................................................... xii 1 . ARE WE HEADING TOWARDS A DESTRUCTION OF OUR ENVIRONMENT? OR IS THERE STILL TIME TO MAKE A DIFFERENCE.................................... 1 2. INTRODUCTION 2 .1 W hat is a straw bale?............................................................................................... 6 2 .2 History o f straw bales............................................................................................... 9 2 .3 W hy use strawbales?............................................................................................. 11 3. STRAWBALE BUILDING SYSTEMS 3 .1 Types o f structures b u ilt w ith straw bales........................................................... 13 3 .2 Types o f bales used fo r building - Selection C riteria........................................ 18 3 .3 Building Systems 3.3.1 Non-load bearing.................................................................................................. 19 3.3.1.1 w ith tim ber frame.................................................................................................21 3.3.1.2 w ith steel frames..................................................................................................23 3.3.1.3 w ith concrete frame.............................................................................................. 24 3.3.2 Load Bearing........................................................................................................ 26 3.3.2.1 Threaded Rods......................................................................................................29 3.3.2.2 Wire rope, cable and strapping............................................................................ 31 3.3.3 Hybrid.................................................................................................................. 32 3.3.3.1 Structural Hybrids.................................................................................................33 3.3.3.2 Compositional Hybrids.......................................................................................... 35 3.3.3.3 Temporal Hybrids................................................................................................. 35 iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4. BALE BUILDING COMPONENTS 4 .1 W alls........................................................................................................................ 37 4 .2 Roofs and Ceiling...................................................................................................40 4.2.1 Traditional Roof Types......................................................................................... 40 4.2.2 Domes................................................................................................................. 46 4.2.3 Vaults.................................................................................................................. 47 4 .3 Finishes................................................................................................................... 49 4.3.1 Cement Stucco..................................................................................................... 50 4.3.2 Lime Plasters....................................................................................................... 51 4.3.3 Clay and Earth based plasters............................................................................. 52 4.3.4 Gypsum plasters...................................................................................................52 4.4 Openings..................................................................................................................53 4.4.1 Openings in load-bearing walls........................................................................... 54 4.4.2 Openings in non load-bearing walls.................................................................... 57 4 .5 Foundations............................................................................................................ 58 4.5.1 Slab-on-grade......................................................................................................59 4.5.2 Perimeter Walls.....................................................................................................60 4.5.3 Pier Foundations..................................................................................................61 5 ADVANTAGES OF STRAWBALES 5 .1 Sustainability......................................................................................................... 62 5 .2 A vailability.............................................................................................................. 62 5 .3 Pollution re d u c tio n -In n o v a tiv e use o f a w aste resource............................ 64 5 .4 Low Embodied Energy.......................................................................................... 65 5 .5 C ost..........................................................................................................................66 5 .6 Insulating properties............................................................................................ 68 5 .7 Ease o f Construction..............................................................................................69 6 PRECAUTIONS AND DISADVANTAGES 6 .1 Moisture................................................................................................................... 71 6.1.1 W ater and Straw - The Capillary Mechanism........................................................71 6.1.2 Sources o f moisture damage................................................................................72 6.1.3 Wind-driven moisture penetration........................................................................ 73 6.1.4 Vapor barriers...................................................................................................... 74 6.1.5 Precautions........................................................................................................... 75 iv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.2 Fire S afety................................................................................................................76 6.3 S torage.................................................................................................................... 76 6.4 S eism ic Per fo rm ance .............................................................................................77 6.5 P erm its and Codes.................................................................................................80 7 TESTS ON STRAWBALES 7.1 F ire............................................................................................................................83 7.1.1. SHB AGRA, INC E-119 Small Scale Fire Test, New Mexico, 1993........................83 7.2 M o istu re ................................................................................................................... 85 7.2.1 Canada Mortgage and Housing Corporation, Ottawa, Ontario, Canada................. 85 7.2.2 Portland Community College - Straw Bale Construction Research P roject........... 86 7.3 S eism ic.....................................................................................................................90 7 .4 S tru c tu ra l 7.4.1 Ghailene Bou-Ali Tests......................................................................................... 91 7.4.1.2 Compressive Test Results.................................................................................... 93 7.4.1.3 In-plane Lateral Loading...................................................................................... 94 7.4.1.4 Out-of-plane la te ra l Loading............................................................................... 94 7.5 T herm al................................................................................................................... 95 7.5.1 McCabe Tests.......................................................................................................95 7.5.2 Other Tests..........................................................................................................95 8 THESIS — THERMAL TESTS ON STRAWBALES 8.1 H ypothesis.............................................................................................................. 98 8 .2 R elevance o f t es ts..................................................................................................98 8.3 M ethod o f T e stin g .................................................................................................. 98 8.3.1 The Heat Source................................................................................................ 102 8.3.2 Nomenclature..................................................................................................... 103 8.3.3 Test Sequence 8.3.3.1 Test 1 - w ith 3W Lamp....................................................................................... 104 8.3.3.2 Test 2 - w ith 5W Lamp....................................................................................... 105 8.3.3.3 Test 3 - Second run w ith 5W Lamp...................................................................106 8.3.3.4 Test 4 - w ith 7W Lamp....................................................................................... 108 8.3.3.5 Test 5 - Second run w ith 7W Lamp...................................................................I l l 8.3.3.6 Test 6 - w ith 15W Lamp.................................................................................... 114 8.3.3.7 Test 7 - w ith 25W Lamp...................................................................................117 8.3.3.8 Test 8 - w ith 25W lamp (bale laid fla t).............................................................. 119 V Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8.3.3.9 Test 9 - w ith 15W lamp (bale laid fla t).......................................................... 121 8.3.3.10 Test 10 - with 7W lamp (bale laid fla t).......................................................... 123 8.3.3.11 Test 11 - Second run w ith 7W lamp (bale laid fla t)........................................126 9 CONCLUSIONS...................................................................................................... 128 10 BIBLIOGRAPHY 10.1 Books..................................................................................................................131 10.2 Journals............................................................................................................. 131 10.3 Websites............................................................................................................ 132 11 APPENDIX 11.1 C alifornia State Health and Safety Code 18944 11.1.1 18944.30..........................................................................................................133 11.1.2 18944.31..........................................................................................................134 11.1.3 18944.32..........................................................................................................135 11.1.4 18994.33..........................................................................................................135 11.1.5 18994.34..........................................................................................................136 11.1.6 18994.35..........................................................................................................136 11.1.7 18994.40..........................................................................................................137 vi Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES Fig. 1: Three-string bales__________________________________________________ 7 Fig. 2: D ifferent bale positions_______________________________________________8 Rg. 3: Standard Dimensions o f Two and Three-string bales________________________ 8 Fig. 4: Load-bearing bungalow______________________________________________ 13 Fig. 5: Uul-Bayan Health Clinic w ith large Southern windows, Ul aanbaat ar , M ongol i a 14 Fig. 6: Strawbale octagon, the firs t code perm itted building in North Carolina___________14 Fig. 7: Wine Storage building, Mudgee, NSW A ust ral i a____________________________ 14 Fig. 8: Straw bale bed-n-breakfast, D ayi esf ord, V i ct ori a A ust ral i a____________________ 15 Fig. 9: A strawbale greenhouse, A ust ral i a______________________________________15 Fig. 10: Strawbale residence w ith a curved roof, M t Ver non W ashi ngt on______________ 16 Fig. 11: The Heartwood Institute Meditation Temple. This is a private holistic healing 16 arts school, which used wheat straw bales, Cl ar em ont , C A Fig. 12: The Bob Munk residence, a 3800 square-foot house, Sant a Fe, CA ____________ 17 Fig. 13: The Richard Hughes and Clare Rhoades residence, Sant a Fe, C A _____________ 17 Fig. 14: The Tom and Kathy Noland House, Owens Val l ey, C A ______________________ 17 Fig. 15: Connecting bale wall to post w ith expanded metal lath_____________________ 21 Fig. 16: The box column and the box column assembly__________________________ 23 Fig. 17: EO S Institute’s Straw bale Demonstration Eco-House, Anahei m , CA, 1993_ _ _ _ 24 Fig. 18: Concrete block columns and concrete bond beam, Dry-stacked concrete______ 25 block column w ith concrete bond beam cap, Dry-stacked concrete block comer columns Fig. 19: Strawbales replace the wood-frame walls common in most North___________ 27 American construction Fig. 20: Wall section w ith all-threads________________________________________ 30 Fig. 21: All-thread connected to anchor b o lt w ith a coupling nut___________________ 30 Fig. 22: Cable and polyester strapping used to anchor the roof plate________________ 31 v ii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 23: A typical "Structural" Hybrid_________________________________________ 33 Fig. 24: Structural hybrid__________________________________________________ 34 Fig. 25: Compositional Hybrid_______________________________________________ 35 Fig. 26: "Temporal" Hybrids - R etrofit Type_____________________________________36 Fig. 27: Bracing o f plastered straw bale skin____________________________________38 Fig. 28: Various wall pinning strategies________________________________________39 Fig. 29: Vented hip roof, Kate Brown's load-bearing pottery studio,__________________ 41 San Lor enzo, New M exi co Fig. 30: Gable roof on Joan Chandler's house, G i l a, New Mexi co____________________ 41 Fig. 31: Shed roof, Bill and Athena Steen’s guest house, Canet o, Ar i zona_____________ 42 Fig. 32: Clerestory roof a t Seeds o f Change Farm, Gila, New M exi co_________________ 43 Fig. 33: Modem Pueblo-style fla t roof, Catherine W ell's Studio, nort hern New Mexi co 44 Fig. 34: Bales being placed fo r a living roof, Quebec, Canada______________________ 45 Fig. 35: Experimental straw bale dome in Canet o, Ari zona_________________________47 Fig. 36: An experimental straw bale vault house, Experimental Strawbale vault designed_48 and b u ilt by Dan Smith and Bob The is o f Berkeley, California Fig. 37: Shear mechanism developed by David Mar fo r compression struts in a vaulted 49 strawbale wall assembly Fig. 38: Rounded window opening w ith transom vent above, Window seat___________ 54 Fig. 39: Box beam doorframe______________________________________________ 55 Fig. 40: Ladder-type steel lintel_____________________________________________ 56 Fig. 41: Non-Load bearing doorframe and Lintel_________________________________57 Fig. 42: Straw bale wall footing w ith moisture proofing___________________________ 58 Fig. 43: A typical slab-on-grade foundation_____________________________________59 Rg. 44: Perimeter wall foundations__________________________________________ 60 Fig. 45: Pier foundations can use concrete o r wooden piers to support a floor framework_61 v iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Rg. 46: Locations o f straw bale buildings in the US in 1995________________________ 63 Fig. 47: Simple techniques like increasing roof overhangs on walls exposed to_________ 73 frequent rains can adequately protect the bales from moisture Fig. 48: Keyed Plates______________________________________________________ 79 Fig. 49: Bond Beam_______________________________________________________ 80 Fig. 50: Construction Details fo r the Portland Community College___________________ 87 Fig. 51: Above Left: Moisture Content a t the Exterior of the W all, Moisture Content_____ 88 a t the Center o f the Wall Fig. 52: Comparison o f the Moisture Contents fo r the North and South Walls__________ 89 Fig. 53: The Test Frame___________________________________________________ 91 Fig. 54: The Loading Diagram______________________________________________ 92 Fig. 55: A 12-foot by 8-foot w all test panel____________________________________ 94 Fig. 56: Phantom drawing o f general experiment set-up, showing positions o f_________ 100 temperature sensors Fig. 57: Location o f Temperature Sensors on the Outside o f the Test_______________ 101 Cell (prior to sealing) Fig. 58: Location o f Temperature Sensors inside the Test________________________ 101 Cell (when the bale is laid on edge) Fig. 59 Section o f test cell w ith bale laid fla t (thk = 23")_________________________ 103 Fig. 60 Section o f test cell w ith bale laid on edge (th k = 15 1/2")__________________ 104 Fig. 61: Inside (T ) and outside (T0 ) temperature graphs fo r Test 1_________________ 105 Fig. 62: Inside (T ) and outside (T0 ) temperature graphs fo r Test 2_________________ 106 Fig. 63: Inside (T ) and outside (T0 ) temperature graphs fo r Test 3_________________ 107 Fig. 64: Temperature differential between inside and outside o f test cell_____________ 108 Fig. 65: Inside (Ti), middle (T„) and outside (T0 ) temperature graphs fo r Test 4________109 Rg. 66: ATS and ATd - Temperature differentials fo r Test 4_______________________ 110 Fig. 67: Ratio o f temperature differential from strawbale to styrofoam fo r Test 4______ 110 Fig. 68: Inside (T ), middle (T „) and outside (T0 ) temperature graphs fo r Test 5________111 ix Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 69: ATS and ATd - Temperature differentials fo r Test 5_______________________ 112 Fig. 70: Ratio o f temperature differential from strawbale to styrofoam fo r Test 5______ 112 Fig. 71: Inside (Ti), middle (Tx ) and outside (T0 ) temperature graphs fo r Test 6_______ 115 Fig. 72: ATS and ATd - Temperature differentials fo r Test 6_______________________ 115 Fig. 73: Ratio o f temperature differential from strawbale to styrofoam fo r Test 6______ 116 Rg. 74: Inside CH), middle (Tx ) and outside (T0 ) temperature graphs fo r Test 7_______ 117 Fig. 75: ATS and ATd - Temperature differentials fo r Test 7_______________________ 117 Fig. 76: Ratio o f temperature differential from strawbale to styrofoam fo r Test 7______ 118 Rg. 77: Inside (T ), middle (T„) and outside (T0 ) temperature graphs fo r Test 8_______ 120 Rg. 78: ATS and ATd - Temperature differentials fo r Test 8_______________________ 120 Rg. 79: Ratio o f temperature differential from strawbale to styrofoam fo r Test 8______ 121 Fig. 80: Inside (T,), middle (Tx ) and outside(T0 ) temperature graphs fo r Test 9_______ 122 Rg. 81: AT* and ATd - Temperature differentials fo r Test 9_______________________ 123 Fig. 82: Ratio o f temperature differential from strawbale to styrofoam fo r Test 9______ 123 Fig. 83: Inside (Ti), middle (Tx ) and outside(To) temperature graphs fo r Test 10______ 124 Rg. 84: AT* and ATd - Temperature differentials fo r Test 10______________________ 125 Rg. 85: Ratio o f temperature differential from strawbale to styrofoam fo r Test 10_____ 125 Rg. 86: Inside (T,), middle (Tx ) and outside(T0 ) temperature graphs fo r Test 11______ 126 Rg. 87: AT* and ATd - Temperature differentials fo r Test 11______________________ 127 Fig. 88: Ratio o f temperature differential from strawbale to styrofoam fo r Test 11_____ 127 x Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES Table 1: Ecological Footprints o f Selected Countries_______________________________3 Table 2: Consumption o f Selected Resources fo r Construction_______________________ 4 Table 3: North American Straw Production______________________________________63 Table 4: Annual Carbon Monoxide Production from Power Plants and Straw___________ 64 Burning (in tons) Table 5: Embodied Energy in Various Wall Insulation Materials_____________________ 65 Table 6: Outline Range o f Straw-Bale Construction Costs per Square Foot (sf)_________ 67 Table 7: Life cyde costs (all figures in $US dollars)_______________________________68 Table 8: Small Scale E-119 Fire Test - Exterior Skin Temperatures___________________ 84 Table 9: Straw bale R-values_______________________________________________ 97 Table 10: Table o f R-values using the tem perature gradient method________________ 129 x i Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT THERMAL PE RFORMANCE OF STRAW BA LE S This thesis is about the thermal performance o f wheat straw-bales. Straw-bales have different insulation values depending on the direction in which the bale fibers are oriented. The experiments performed on the bale attem pt to test the insulation value o f a three-string wheat bale using the relationship between R-value and the temperature gradient across different surfaces. For this, it is essential to Know the R-value o f one o f the surfaces. The bale is placed in an insulated box w ith a heat source, such that heat flows predominantly across the w idth o f the bale. The bale can be laid either fla t (in this position, its w idth is 23 inches and height is 15 1/2 inches) or on edge (in this position, the width is 15 1/2 inches and the height 23 inches). The goal o f this program is to help builders to decide which way to orient bales in wall assemblies fo r maximum thermal efficiency. Keywords; Straw-bales, R-value, temperature gradient, bale orientation Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1. ARE WE HEAPING TOWARDS A DESTRUCTION OF OUR ENVIRONMENT? .....O R IS THERE STILL TIME TO MAKE A DIFFERENCE There is an increasing demand for non-conventional building methods and materials. Strangely these are often referred to as "new” when they have been used fo r building fo r centuries. These alternatives to conventional wood-frame and steel-fram e construction may include adobe, cob, rammed earth, lig h t day, straw-bale and other hybrid systems. This increased demand is a response to the realization that we are tost approaching a period when the materials we rely upon w ill no longer be available. Over the years we have turned a blind-eye to the enormous strain that steel and concrete construction has placed on non renewable resources. Many o f us are also oblivious to the hidden energy costs o f using materials th a t have a very high embodied-energy content In contrast to the pervasive dependence on mechanical heating, cooling and ventilation which uses up vast amounts o f polluting energy, buildings b uilt w ith alternative materials are sensitive to the site, the sun and the prevailing winds and to the changing seasons. Daylighting and natural ventilation are preferred as the architect attem pts to integrate the structure w ith its surrounds. There is also the added aesthetic appreciation o f materials in th e ir m inim ally processed states, the beauty and the fam iliar feel o f raw earth, uncut stone and woven grasses th a t results in architecture that is inspired by natural patterns and the sp irit o f the space created. The ecosystem on the planet that is most threatened by human exploitation are the natural forests. We have, since the beginning o f tim e, lost nearly half (approxim ately 46% ), o f the forests th a t in itia lly covered the earth's surface and deforestation continues a t an alarming l Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. rate and most o f these forests were cut down during the tw entieth century either fo r tim ber or fo r other uses. Between 1980 and 1990 alone, 200 m illion hectares - equivalent to an area larger than the size o f Mexico - were destroyed and only 22% remains o f the world's ecologically intact, undisturbed natural forests. All o f this 200 m illion hectares, was however, not virgin forest. In the United States, a lo t o f replanting is being undertaken. Unfortunately, there is degradation in the quality o f tim ber from replanted trees. Ancient forests support roughly half o f the world's bio-diversity in addition to cleaning our air, stabilizing our clim ate and maintaining our soil. Wood frame residential building in the US is a leading cause o f deforestation w ith the wood being used fo r industrial wood - th a t is the manufacture o f paper, lumber and plywood. In the U S tim ber framing became popular only after the Second World War because it was expedient and cheap. Light tim ber fram ing has become popular in other parts o f the world only recently, unfortunately a t a tim e when forests are being denuded a t an unprecedented rate. Many o f these countries have a rich supply o f other natural materials such as stone and indigenous building systems. Despite the urgent need to stop the deforestation, even poor quality tim ber a t high prices is in great demand. The warning signs - diminished tim ber quality and high prices - are few and provide little incentive to change construction practices.1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. WORLD 5.892.480.000 Bangladesh 125.898.000 0.7 0.6 - 0.1 Brazil 167.046.000 2.6 2.4 - 0.1 Canada 30.101.000 7.0 8.5 1.5 China 1.247.315.000 .2 1.3 0.1 E g y p t 65.445.000 1.2 0.6 -0.5 Ethiopia 58.414,000 1.0 0.9 - 0.1 Germany 81.845.000 4.6 2.1 -2.5 India 970.230.000 0.8 0.8 0.0 Indonesia 203.631.000 1.6 0.9 -0.7 Japan 125.672.000 6.3 1.7 -4.6 Mexico 97.245.000 2.3 1.4 -0.9 Netherlands 15.697.000 4.7 2.8 -1.9 New Zealand 3.654.000 9.8 14.3 4.5 Nigeria 118.369.000 1.7 0.8 -0.9 Russian Federation 146,381,000 6.0 3.9 - 2.0 Thailand 60.046,000 2.8 1.3 -1.5 Turkey 64.293.000 1.9 1. 6 -0.3 United Kingdom 58.587.000 4.6 1.8 - 2.8 United States 268.189.000 8.4 6.2 - 2.1 Table 1“ Ecological Footprints o f Selected Countries Other threats caused by industrialized construction are ill health caused by toxins in buildings and pollution generated by the extraction and manufacture o f building materials. Transportation o f raw materials th a t are used to manufacture building materials and transportation o f these finished products to the site are themselves big contributors to energy consumption and environmental pollution. 3 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. M a te ria ls = « ' ; ; KKyCMO TTwVli :, Scrao End t in .G b h s u m p tlo ii 20% Transportation 36% Packaging 25% Construction and electrical 14% Electrical 8% Consumer Durables and other 17% Insignificant Roofing Products 48% Friction Products 29% Gaskets 17% Other 6% Small amount concrete Readi-mix concrete 70% Concrete products 10% Road-paving contractors 10% Other construction 10% Insignificant Construction 55% Paper 13% Foundry and non-construction refractory 8% Other 24% Construction 42% Electric and electronic 25% Industrial and Transportation 24% Consumer Products 9% Insignificant Construction 83% Chemical and Metallurgical (indudes cement and lime manufacture) 14% Agricultural and other 3% Small amount Construction (wallboard and cement) 81% Agricultural 10% Other 9% Limited pavement recycling Construction 97% Industrial 3% _____________ 61% Warehouses and distributors 21% Construction 14% Transportation 13% Other 52% Table 2" Consumption o f Selected Resources fo r Construction Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The 1990s have witnessed the rise o f the "cu lt” o f sustainability (a much abused and little understood word), a word which is today used to describe alm ost any enlightened response to environmental, social o r economic concerns. Sustainability is rapidly being adopted as a policy by nearly every institution and a t its core lies a realization that the existing operating system o f our society is not capable o f being maintained a t its current pace or in its current form . Building w ith locally derived naturally existing materials is a response to the crisis th a t faces the earth today. It significantly reduces dependency on tim ber and the secondary resources needed fo r manufacture, processing and transportation o f conventional building materials. Designed w ith natural heating and ventilation, alternative construction materials can greatly reduce our energy consumption and pollution. Low impact housing should not be associated w ith poverty or sub-standard housing. Building w ith natural materials is not ju s t about materials and wall assemblies. I t is an approach tha t encompasses a broad set o f ethics defined by a view that the earth is not only sacred but also a balanced ecosystem. Its primary concern is what constitutes a healthy b u ilt environment and how this can be used to nurture a sense o f community. A t its core lies the knowledge th a t the world belongs not to any individual but to mankind collectively and th a t each o f us needs to assess the impact o f our actions and act accordingly. ‘ Ly nn e El iza be t h and C as sa n d ra Ad am s, Al t er nat i ve Co n s t r u c t i o n - Co n t e mp o r a r y Nat ur al BuOtMno Me t h o d s . (Jo hn Wil ey & S o ns ) pp. 5-8 * Pop u la t io n fi gur es are taken f r om the Wo rl d R eso urc es I nstitute, 1996. Wo r l d R e s o u r c e s 1996- 1997 Da t a b a s e , Was hington, D. C. : WRI . Fil e "hdl6101.wkl* * S o u rc e : U S G S 5 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2. INTRODUCTION 2.1 W hat i» a straw bale? Strawbales are rectangular bundles o f plant stems o f varying sizes. Straw is the plant structure between the root crown and the grain head and can refer to ju s t about any grass tha t grows. However, in the construction industry straw typically refers to agricultural grain. The molecular structure o f a straw grain is tough, tubular and efficient - it contains cellulose, hemicellulose, lignins and silica and is springy in bending and has a high tensile strength. The tubular structure is inherently stable w ith a microscopically waxy coat that is slightly hydrophobic. Straw bales are compressed masses o f straw le ft over after the grain heads are removed (it is essential to ensure removal o f grain heads which attract rodents and other bacteria and readily ro t when m oist - these grain heads make straw potentially attractive to animals as a source o f food). The straw is harvested from the field and then fed into mechanical balers, which compress the straw into rectangular blocks, which are bound by steel wire or polypropylene tw ine. Polypropylene is the preferred choice fo r ties because it is strong and durable and not prone to rust. Bales may be two or three-string made from any kind o f grain - in North America typically wheat, rice, oat, hops, barley or rye). The bales are not homogenous, that is to say th a t they have a different property in different directions depending on the orientation o f the grains. The narrow end faces o f the bales receive the compression o f the bale head, which thrusts the straw masses in parts into the chamber. Each part, when compressed, becomes a "flake" o f about four inches thick. These flakes are compressed along the bale's long axis and therefore bale lengths typically vary by about four inches. 6 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Rg. 1 Three-string bales Bales can be laid fla t or on edge. There are advantages to both methods o f bale orientation. Bales laid fla t are more stable and can carry greater loads because simple geometry makes the bales more widely based and also because the grains run prim arily horizontally. Flat bales are also better fo r plastering because the cut exposed straw ends form a better bond w ith the plaster. Bales laid on edge place the ties in tension, which becomes the available lim it o f the load that the bale edge can carry. Furthermore, these ties are exposed along the face o f the wall, which makes them more vulnerable to damage from fire and breakage (an unbound bale has practically no fire resistance and unless adequately surrounded by plaster, has no structural value). However, bales laid on edge provide more interior, useable space and require narrower foundations. Construction w ith this type o f bale placement also requires fewer bales. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. bale laid bale "on edge" "flat" Fig. 2 D ifferent bale positions Three-string bales are typically 46" (length) by 23" (w ide) by 16" (height), when laid fla t, and weigh about 80 lbs. Two-string bales are sm aller w ith length 36" by 18" width and 14" height and weigh from 45 to 50 lbs. Tun S tring Bal e, fig n n , 1 Thru, String f i g n n , 2 Fig. 3 Standard Dimensions o f Two and Three-string bales 8 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.2 H irto rv o f straw bales As long as humans have been building shelters, straw and grass have probably been used widely fo r construction in rural situations, to provide safe and comfortable housing in many climates and environments. Walls made from bundles o f long lengths o f straw, stacked in mud mortar have been used fo r centuries in Asia and Europe. In the United States, straw began being used in construction in the 1800s. Hand operated hay presses were patented in the US before 1850 and by the late 1800s the development o f the stationary horse and steam powered balers made it possible to compress bales into string or w ire-tied bundles called bales. By about 1884, steam powered balers were available, but the horse-powered versions continued to be used in the Great Plains through the 1920s. Although, there w ill probably never be any available documentation on the firs t permanent bale-walled building, it seems likely that its creator was a homesteader, who arrived on the treeless grasslands o f the Great Plains in desperate need o f quick and inexpensive protection from the harsh climate. According to bale-building researcher Roger Welsch, the oldest documented building was a one-room schoolhouse b u ilt near Bayard, Nebraska in 1886 or 1887. The oldest existing straw-bale building is the Burke homestead built near Alliance, Nebraska in 1903 and occupied by the fam ily till 1956 when it was abandoned. The exterior walls were le ft unplastered fo r the firs t ten years. Even though the building has not been maintained, it has withstood almost a hundred years o f varying temperatures and blizzards. It s till stands today in relatively good but deteriorating condition. Although bale buildings were b u ilt all over the US, they flourished in the Sandhills o f Nebraska as nowhere else. I t could be argued th a t bale construction was an appropriate response to a unique combination o f legislative, geologic, natural resource and socio- 9 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. economic factors that prevailed in th a t region in the early 1900s. From a legislative point o f view, the Kincaid Act o f 1904 opened up part o f Nebraska to homesteaders under new laws th a t enabled applicants to claim a fu ll section (one square m ile) rather than the quarter section previously allowed. This resulted in the arrival o f a large number o f financially pinched homesteaders in a treeless, semi-arid region characterized by vast roadless grasslands. A combination o f low elevation and therefore a high water table, greater amounts o f day in the soils and perched groundwater enabled this region to provide decent sod fo r building. However, calculations reveal that a moderately sized house would require a huge amount o f sod fo r building; sod whose hay yield was critical to the survival o f cattle especially since it would take several years fo r the area to naturally reseed itse lf and reach fu ll productivity. By contrast, using bales fo r building gave the settler the option to do an early harvest fo r w inter feed and then allow the grasses to regrow. Killed by the firs t hard frost, this dry dead grass could then be cut and baled fo r building w ithout a loss o f production in subsequent years. In itia lly many o f the houses were constructed as a stopgap measure to provide shelter in the shortest possible tim e fo r the least possible money. These houses were often le ft exposed on the outside and plastered on the inside. When the owners finally realized that they were living in a permanent house, the walls would receive a coat o f plaster. The historic period o f construction fo r straw bales is defined from the firs t structure built fo r human habitation (location and exact tim e unknown) to about 1940. As far as is known, before 1936, all known bale structures in the US were used to support the weight o f the roof (Nebraska style). In th a t year Dr. W illiam Henry B urritt b u ilt a tw o-story bale mansion in Huntsville, Alabama using tim ber posts and beams as the supporting framework w ith wheat straw bales as the in fill m aterial.' 1 0 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. As o f October 1993, over one hundred bale structures have been documented in Mexico, Canada, Australia, France and England and the US. Climatically the range includes semi-arid, Southern Sonora, Mexico; rainy, humid Alabama, northern California, w intry northern Alberta, Canada and the coast o f Maine.8 The range o f buildings varies from a small storage shed b uilt as a project by fifth graders to elegant homes, an a rt gallery and several others. Although most o f these buildings were constructed w ithout any codes, guidelines or inspections, the number o f legal code-permitted buildings is steadily increasing. Numerous tests have been performed and continue to be performed on straw bales and these may lead to the eventual acceptance o f this construction method fo r load bearing walls in residential structures. 2 .3 Whv Use Strawbales Environmental impacts are not all equal. Some are more critical and have more widespread consequences than others and should be given more weight. • Sphere o f influence - Some impacts have a more widespread impact such as global warming. • Duration - Some impacts are short term while others could have long lasting effects e.g. nudear waste dumps and dumping waste into seas and rivers. • Risk to human or ecosystem health - Some impacts can be seriously detrimental to health such as toxic waste dumps. • Reversibility - Some impacts are irreversible while others can be repaired using technology. 1 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Straw-bale building systems are not responsible for any o f the above-mentioned impacts; on the contrary they have a positive impact on the environm ent Bales are readily available and their use is beneficial to the environment because straw is an abundantly available waste material, which if not used is burnt. This releases particles into the a ir, which is a source o f pollution. Therefore, using bales as a building material serves the dual purpose o f providing an innovative use o f a waste material and reduction o f environmental pollution. They have a wonderful feel o f being dose to nature and when kept dry, pose no health risk a t all; they are non-toxic. Bale walls provide excellent sound and thermal insulation, making them an attractive solution fo r urban settings where noise is disturbing and unhealthy. Inside a straw house, the walls provide a pleasant sound and feel that is unavailable from fla t, drywalled interiors. Straw bales almost negligible embodied energy and so there are no "unseen" consequences - they are also readily available almost all over the US, so transportation costs are greatly reduced. Straw can be grown and harvested annually, making it a renewable resource. Fields can continue to produce building material year a fte r year - unlike forests which may take up to 50 years to regenerate and rarely produce the original high quality tim ber. There are numerous other advantages when compared to conventional building materials in term s o f both energy and quality o f space. Building w ith bales is rapidly gaining momentum as more people come to realize its benefits and that this building system m ight provide a solution to the energy crisis. ' The Last Straw, vol. 2, Fail 1993; Networks Productions, Inc pp. 17,19 1 1 The Last Straw, is s u e no. 6, S p rin g 1994; Networks P roductions, Inc pp. 17 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3. STRAWBALE BUILDING SYSTEMS 3 .1 Types O f Structures B uilt W ith Strawbalcs Building w ith bales is no longer confined to residential applications. Over the years straw bales have been used fo r a wide variety o f buildings ranging from small and large houses to schools, clinics and some commercial applications. Their fle xib ility in accepting different finishing materials and their ability to adapt to other systems such as earth-sheltered and solar systems have greatly increased th e ir popularity. Some interesting structures built w ith bales are given below: Fig.4 Load-bearing bungalow. This residence has an uninterrupted, straight wall 75' long and a dear span width fo r the trusses over 40'. Nor wood, O nt ari o 13 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. V . r * Fig. 5 Uul-Bayan Health Clinic w ith large Southern windows, U l aanbaat ar , M ongol i a Fig. 6 Strawbale octagon, the firs t code perm itted building in North Carolina Fig. 7 Wine Storage building , Mudgee, NSW A ust ra l i a 14 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 8 Straw bale bed-n-breakfast, D ayt esf ord, V i ct ori a A ust ral i a Fig. 9 A strawbale greenhouse, A ust ral i a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 10 Strawbale residence with a curved roof, M t Ver non W ashi ngt on Fig. 11 The Heartwood Institute Meditation Temple. This is a private holistic healing arts school, which used wheat straw bales, Cl ar em ont , CA 1 6 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 12 The Bob Munk residence, a 3800 square-foot house, Sant a Fe, CA Fig. 13 The Richard Hughes and Clare Rhoades residence, Sant a Fe, C A Fig. 14 The Tom and Kathy Noland House, Owens Val l ey, C A 17 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.2 Tvpcs Of Bales Used For Building - Selection C riteria W ith the several varieties o f bales available in varying sizes, selecting good bales fo r construction can be daunting. There are a few precautions that can be taken when selecting bales to ensure that they are fa irly uniform and o f a good quality. • Tightness - Bales fo r building should be fa irly tight. Bales are tied w ith either polypropylene string, wire or sisal tw ine and really tig h t bales use less tw ine to bind the entire assembly, but are heavier and harder to handle. The choice o f tie is vita l to the strength o f the bale and directly affects its solidity. Generally polypropylene tw ine is most preferred because it is very strong. Sisal tw ine being prone to ro t is usually used as a last resort. Farmers can adjust baling machines to improve tightness. Bale tightness can be assessed by either scientific or low-tech methods. To find out if the bale is tig ht, when liftin g the bales, the ties should not separate from the bales by more than 4-5 inches. The bale should also maintain its integrity when lifted by one string. Scientific definitions o f bale tightness in the Arizona and California Straw Bale Codes specify that "bales shall have a minimum calculated dry density o f 7.0 pounds per cubic foot". Densities over 8.5 pounds per cubic fo o t are thought to lower the insulation value o f the bales by elim inating spaces between the stalks that entrap air. • Dryness - Bales should be dry. Like any organic m aterial, straw w ill decompose under prolonged conditions o f moisture. Dryness can be assessed quickly by opening the strings and looking inside the bales. Check if the straw is damp to touch, if it smells damp o r if there are any visible signs such as black mold. Bales should be carefully stored in a dry, cool space w ith precautions to prevent exposure to m oisture. For a scientific assessment o f dryness, moisture meters can be used. These instruments give fa irly accurate results. 18 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. • Size - Size is the least im portant consideration and it does not really m atter if the bales used are two-string or three-string as long as they are consistent This is to ensure th a t the height and w idth o f the bale wall does not vary too much. The above three basic characteristics are the most im portant. In addition to these, there are some less im portant characteristics. The bales should be largely free o f seed heads that attract rodents and other pests. The bales should be about twice as long as they are wide to ensure th a t they w ill stack up in a true running bond. Select bales th a t are made up of stems th a t are a t least 10 inches long and predominantly tubular in shape. Avoid using bales consisting o f short, shattered stems th a t don't hold together as a flake because these tend to be messy (fire hazard), and may not have a very high structural integrity. 3.3 Building Systems 3.3.1 Non-Load Bearing A non-load bearing wall system is one in which the weight o f the roof structure is supported by another m aterial and not the straw bales. The bales are used only as in fill material and are required to support their self-weight and remain intact under lateral loads. There are both advantages and disadvantages to this system. Advantages • Greater fle xib ility in design allowing m ultiple stories, larger roof spans, higher design loads, larger and more window and door openings and the ab ility to make additions to the building in the future. 19 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. • Since the roof framework can be erected before the bales are set in, they provide a dry shaded place fo r storing the bales. This would allow work to continue even when it is raining. • The option o f using bales on edge (since the bales do not carry any structural loads) which saves interior space and requires fewer bales. • Eliminates the need to pre-compress walls or w ait fo r walls to settle. Consequently, finishing coats can be applied as soon as the wall has been erected. • Greater acceptance by code officials because the structural load is not carried by the straw bales. Disadvantages • The expenditure o f extra tim e, money, materials and labor to erect the structural framework. This also requires more knowledge and skills than an owner-builder may possess. • The need to create a more complex foundation system to carry the concentrated loads from the vertical posts. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.3.1.1 W ith Timber Frame a P A M P l P H C T * . LATWt NAIUCP r e I W T A M O Fig. IS Connecting bale wall to post w ith expanded metal lath This is the most common type o f non-load bearing system used in bale construction. The dassic tim ber frame can be very beautiful but increases the cost and is tim e consuming. It also requires a higher level o f expertise and there is also the consideration o f the environmental impact o f using more lumber, often o f a higher quality. A wide variety o f conventional milled 4-by-4, 4-by-6 and 6-by-6 posts induding u tility posts, lodge poles and tim ber bamboo have been used fo r the structural framework. Posts can be either on the exterior or the interior side o f the wall and the tim ber framing can be le ft exposed on the inside o f the building. In simpler structures, posts are sometimes notched into the bales. This is tim e consuming but in some cases can provide the lateral bradng fo r the structure. A 4-by-4 post is the largest post th at can be inset into the bale w ithout having to cut the ties. I f poles are to be inset, the bales must be laid fla t, when the bales are laid on edge, the exposed wires on the surface o f the wall make it impossible to insert the posts. 21 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The in fill panels need to be secured to the structural framework. This is usually done by using metal lath a t every layer o f bale. The lath is nailed to each end bale near the post and to the post using flathead, spiral nails. There are several variations to this type o f construction. One o f these is the m odi f i ed p o st and beam system, shown below, which is one o f the most efficient methods o f building a bale structure in terms o f tim e, material and labor. I t differs from the traditional tim ber post- and-beam construction in that the window and door bucks are constructed as structural supports and distributed throughout the perimeter o f the building. Box columns, the width o f the bale w alls are used as the vertical sides o f the bucks from foundation to the beam. These box columns consist o f a structural frame o f 2-by lumber sheathed with plywood or Oriented Strand Board. The edge o f the box column tha t supports the beam needs to be stronger than the rest o f the frame to support the roof structure. Depending on how this structure is designed and the components used, it can be very competitive with a load- bearing building in every respect. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 16: The box column and box column assembly 3.3.1.2 W ith Steel Frames To date, metal fram e systems have rarely been used in conjunction w ith bale walls. Metal columns and I-beams can undoubtedly provide an adequate structural framework to support roof loads. They have been commonly used in the building industry and are building code rated. It is quite possible to find used or surplus components a t reasonable rates (reducing concerns th a t using large quantities o f metal in houses is not sustainable). Uprights can be small enough to be set into small notches in the joints between the bales, providing a continuous and unbroken plastering surface. There are two options fo r connections in steel framework. Most contemporary steel calculations are based on a standard product called A36 structural steel where all 23 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. connections must be welded or bolted. Most building codes require a certified welder to do welding jobs. Bolted connections require that the steel be pre-sized and pre-punched a t the supplier's yard. The other disadvantage w ith using structural steel framework is th a t in steel calculations, there is little room fo r error because o f the precision o f the numbers. In bale buildings, precise measurements are not the norm and so complications could arise during construction. The steel in the straw bale wall also reduces the insulation value o f the wall because it forms a therm al bridge for the transfer o f heat. This may be rectified by the use o f styrofoam or other insulation. Steel fram ing, however need not be used throughout the house. I t can be used in combination w ith wooden or concrete posts and beams. Fig. 17 E O S Institute's Straw bale Demonstration Eco-House, Anahei m , C A , 1993 3.3.1.3 W ith Concrete Frames Concrete columns and concrete top plates can be used in conjunction with other m aterials to form all or part o f the structural system supporting the roof loads. Concrete blocks can 24 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. easily be dry-stacked and the hollow space filled w ith cement and rebar when the column has reached its fu ll height This option requires no form work and little experience. Poured columns require form work to contain the w et concrete. It is im portant to use adequate rebar to support the column, irrespective o f whether concrete blocks or poured concrete makes up the column. There are two disadvantages to using concrete columns. First they w ill be visible inside the house after the walls are erected. Secondly, concrete columns form a therm al bridge allowing heat to transfer outside more rapidly, sim ilar to metal frames, lessening the overall insulation value o f the w all. Fig. 18 Above Left: Concrete block columns and concrete bond beam Above Right: Dry-stacked concrete block column w ith concrete bond beam cap Below Right: Dry-stacked concrete block comer columns Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3,3,2 Load-Bearing In load-bearing construction, the weight o f the roof is directly borne by the bales themselves w ithout any additional structural members such as wooden posts or columns. This type o f construction was pioneered in the Nebraska Sandhills w ith the availability o f baling equipment, which facilitated the handling, storage and transportation o f hay. Many o f the old load-bearing structures s till exist today in fairly good condition. In this type o f construction, the bales are stacked in a running bond w ith each bale placed over the vertical jo in t between the bales in the courses above and below it. The bales are pinned together by suitable m aterial, which w ill reinforce the w all. A horizontal structural member, placed on top o f the bales, is used to stabilize the w all, distribute the roof load evenly to the walls and to provide a connection between the roof and the foundation to enable the wall to withstand seismic and wind loads. Advantages • Possible savings o f tim e, money, labor and materials since no additional roof bearing framework is required nor m aterial fo r structural support • Greater ease o f design and construction • Even distribution o f load along foundation and load-bearing walls Disadvantages • Design constraints in type o f roof • The need for dense, uniform bales which have to be laid fla t • Need to w ait fo r bales to reach fu ll compression, unless they can be pre-compressed by some mechanical means 26 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Typical Nebraska, -Style, or Load, Bearing Straw Fig. 19 Strawbales replace the wood-frame walls common in most North American construction Some o f the design constraints stipulated by code for load-bearing structures are: • Maximum moisture content at tim e o f installation should be 20% o f the total weight o f the bale • Maximum calculated dry density should be 7 pounds per cubic foot • Nominal minimum bale wall thickness should be 14 inches • Maximum number o f stories - one • Maximum wall height-to-thickness ratio should be 5.6:1 (fo r a 23 inch thick wall the height would be 10 feet) • Maximum unsupported wall length to thickness ratio should not exceed 13:1 (fo r a 23 inch thick wall the maximum unsupported wall length would be 25 feet) • Maximum area o f openings should not exceed 50% o f the total w all area 27 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. For some structures load-bearing construction may be the most economical method but there are several principles tha t must be kept in mind when building in this way. The most im portant basic principle is that straw-bales are a compressible building material unlike steel and concrete. Under the roof load the bale walls w ill compress - the greater the load, the greater the compression. The density o f the bales, their compactness and the quantity and placement o f openings w ill affect the degree o f compression. For example, when windows and doors are placed in such a way th a t only narrow columns o f bales are le ft between them, these bales may come under greater load than the rest o f the w all. This is especially true when lintels are used over openings because they take the load from over the opening and transfer it to the bales on either side o f the openings. These bales which are already carrying the roof loads may then be subject to double the load which would lead to unequal compression in different parts o f the w all. I t is advisable to avoid isolated bale walls and very long walls w ithout any cross wall (which acts as a stiffener). Precautions should also be taken not to mix non-compressing structural supports w ith load-bearing bales in the same wall section. A s tiff roof plate, which is capable o f withstanding loads w ithout bending in the vertical plane or sagging under the load w ill greatly help in even distribution o f the loads and reduction o f differential settlem ent o f the bales. The early pioneers o f straw-bale construction dealt w ith the problem o f settlement by building the roof over unplastered bale walls and waiting fo r a few weeks fo r the bales to settle. They then plastered the compressed bale walls creating a structural skin, which resulted in remarkably strong and rigid structures. Some people s till use this method but it is tim e consuming (to allow fo r maximum compression, bale walls should be le ft unplastered fo r a t least a week and ideally a month) and not always practical. This method is inappropriate in areas where high winds, snow loads or heavy rains are expected. 28 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Pre-com pression Modem builders use a variety o f methods to "pre-compress" bale walls. This does not require a waiting period and also enables accurate leveling o f the w all. Walls can be plastered over almost immediately. Most o f these methods have a common underlying principle - the foundation o f a building is tied to a continuous, structural roof plate at regular intervals around the building. These ties are then subjected to a force, which draws the roof plate down towards the foundation thereby inducing compression in the bale walls. Even large mechanical loads have usually produced only about ’/* inch o f immediate compression in a wall w ith seven courses o f bales, indicating the high compressive strength o f the bale walls. Properly tensioned, these walls are remarkably strong and resistant to flex in all directions, even before plastering. However, it must be realized th a t long term compression is a very im portant criterion and the architect o r designer must be aware o f its im plications when designing. 3.3.2.1 Threaded Rods This is one o f the most common methods o f creating a continuous connection between the foundation and the roof plate. The rods are attached to the foundation and run up through the interior o f the bales and out the top where they are fastened to the roof plate. At the foundation, W inch anchor bolts embedded into the foundation serve as attachm ent points. The threaded rods are connected to the anchor bolts w ith coupling nuts and spaced no more than six feet apart w ith a minimum o f tw o per wall section. I t is desirable to place the rods w ithin 12 inches o f the comers so th a t the comers get pre-compression as w ell. Paul W einer, architect and builder, had engineering calculations done fo r Vi inch threaded rods in load-bearing walls. Tests showed th a t placement o f the rods every six feet are tw enty times stronger than necessary to withstand 75mph winds. 29 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. *U .'T H * E A D 5 C C T I0 N 3 W ITH C 0U *U N C | N K T » ! * * C t D E VC ftY A* AND t t i r x i * 3% h 0 * w a l l C H 0 S • D C Q t L ftiK X 5 TXUCTulCAL W I N D O W B H O tt ' *4 K lA A t P in* DfUVCN n tftfltfC iH icouwcs e e o iN M iN C i W ITH 4 ” COMteC i* fc J > D 0 C R . J K ip p iN C i T V tl 5 * " COURSE -J»w _ J } W IT H U N T E L t t ' S-STKlNii RA LX3 W A L L S lC T lO M >MlTM A U L-T M lttA D '4 KCBAK. FIN S e m b e d d e d IN FOUNCATION a M i n i m u m OF A -7 " AND O T E N D lN a A M IN IM U M OF 12" IN H C Ib irr t m * B A I . L l Fig. 20 Wall section w ith all-threads I t is recommended th a t heavy steel plate washers o r malleable washers be used under each nut in the threaded locations to spread the force across a larger area o f wood. This method can be time consuming because it is im portant to position the bales precisely over the rods.1 Fig. 21 All-thread connected to anchor bolt w ith a coupling nut 30 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.3.2.2 Wire roue, cable and strapping Other methods fo r anchoring the roof plate to the foundation indude using w ire rope, aircraft cable or polyester strapping. These are run up the surface o f the wall to the roof plate and attached to the foundation on either side o f the w all. There are several strategies fo r attaching cable to the foundation. Three-inch eyebolts spaced not more than six feet apart can be embedded into the foundation w ithin three feet from the end o f the wall w ith a minimum o f tw o eye-bolts per wall section. They should be imbedded in the foundation to a minimum depth o f six inches w ith a nut and washer threaded onto the eyebolt near the end. When wire rope or a ircra ft cable is used, metal comer protectors or wire thimbles may be used at any point where the wire or cable bends around another surface like the roof plate or the eyebolt. Tumbuckles can be used to tighten tee cable and wire rope clamps attach the ends o f the cables together. 'f'*- * j fe f i C TttKOMftH tTtftOLT Fig. 22 Cable and polyester strapping used to anchor the roof plate 31 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Using strapping, wire rope o r cable saves considerable tim e in the stacking o f a load-bearing bale wall compared to using all-thread sections. Bales in the walls can simply be placed w ithout the need fo r exact placement. Tom Luecke o f Boulder, Colorado used polyester cord strapping as an alternative to having any metal in the house to minimize disturbances from electromagnetic fields. Metal actually helps to reduce outside magnetic fields such as those produced by the earth itself. As long as there is no electric current passing through the metal it w ill not produce an electromagnetic field. Strapping can be run over the top o f the roof plate and down each side o f the wall to connecting points in the foundation." 3.3.3 Hybrid Hybrid designs are a combination o f load bearing and in -fill bale wall construction. They represent an attem pt to solve some o f the inherent problems o f load-bearing construction, while attem pting to reduce the amount o f lumber required fo r in -fill walls. Hybrid structures have begun to explore the possibility o f using very thin lumber or bamboo to take the vertical load when braced against the interior and exterior surfaces o f the bale walls as pilasters. This system not only provides efficient use o f materials but may also reduce other problems such as differential settling and the need fo r a s tiff roof plate. Hybrid structures can be sub-divided into three overlapping categories. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 23 A typical "Structural" Hybrid illustrated has a pole framework running down the middle o f the two long walls. This reduces the load per linear foot on the tops o f the two long walls and therefore reduces the compression 3.3.3.1 Structural Hybrids In this system both the compressive bale walls and the non-compressive framework made w ith other materials carry the roof w eight. This system can allow fo r more flexible design fo r e.g. in a single-story house the roof can be supported in the center by an adobe wall while the exterior bale walls can share the remaining load. Or if the South wall o f a building is to have a lo t o f windows fo r solar exposure, it could be constructed using the post-and-beam construction method while the North w all can be built using a load-bearing bale wall. This system could also allow innovative tw o-story buildings where the lower floor is built with post-and-beam structural construction w hile the upper story can use load-bearing straw bale walls to support the roof structure. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. custom inverted tv u s s straw-bale walls, badr and sides stairway partial loft rimmed earth, puddled adobe, or cob rain-water storage loadbearing straight or circular walls support for ridge beam, or central pole in circular structure Fig. 24 Structural hybrid 34 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.3.3.2 Compositional Hybrids This system uses a combination o f different materials. For example a house may be part earth sheltered and part straw-bale o r a building w ith a gable roof carried by two straw-bale walls, where the end walls are an in fill o f cordwood. 3.3.3.3 Temporal Hybrids These are structures in which the old and new are combined. One example would be a re tro fit. You could upgrade an old, uninsulated masonry house that's an energy drain by installing new doors and windows, by adding new ceiling insulation sufficient to superinsulate the roof. Bales can be used either inside o r outside the building depending on the structure. In general, a new foundation is added to the outside o f the existing wall and then a straw-bale wall is put up and fastened to the structure. The eaves often have to be extended over the new addition. Interior retrofits w ith bale walls incorporating reinforced columns and beams may be very effective in reducing the seismic risk o f older unreinforced buildings. This system would also include a new straw-bale addition to an old existing structure b u ilt w ith some other material. loadbearing circular bale wall rammed-earth tire foundation cable tie to resist outward thrust or use central pole support where rafters meet Pit House Fig. 25 Compositional Hybrid 35 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. metal skin- on steel frame - ■ s traw-bale — — insulrtioii — I s • i B wooden or “metal post M etal building or Pole-building K it » « J e & fla t extend e a > Attachments Wrap Existing Structure With Bales Fig. 26 Tem poral" Hybrids - R etrofit type ' Athena Swentzell Steen; B ill Steen; David Bainbridge with David Eisenberg; The Straw Bale House: Chelsea Green P ublishing Com pany, White River Junction, Vermont; pp. 73-74 1 1 Athena Swentzell Steen; B ill Steen; David B ainbridge with David Eisenberg; The Straw Bale H ouse: C helsea Green P ublishing Com pany, White River Junction, Vermont; pp. 74-76 36 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4. BALE BUILDING COMPONENTS 4 .1 W alls The thickness o f bale wall usually makes them inherently strong. I f the walls are not stacked too high or if the walls are not too long w ith cross walls, a bale structure can last fo r a very long tim e, even in high winds. Virtually a ll bale walls are plastered and once this is done the bale wall now acts as a composite element. I t is vital to realize that any imposed snow, wind, earthquake or people loads w ill now be absorbed mostly into the plaster skins. This is because o f the comparative elasticity o f the tw o materials. Plaster is fa r stiffe r than the straw and w ill consequently "attract” any loads. Therefore if there is any imposed load on a plastered straw-bale structure, the flexible straw immediately yields and the b rittle plaster skin absorbs any stresses. Thus if the plaster skin is not strong enough to carry this load, it is likely to crack or buckle. However, unlike in a conventional concrete building where the failure could be sudden and catastrophic, the failure o f the plaster skin causes the load to fa ll back onto the secondary straw-bale walls. The capacity o f the bale wall to carry the load is not precisely known but is considerable. In an earthquake, the bales can act in two possible ways - either the flexibility o f the bale walls make it ideal for damping the dynamic shaking or the bale wall may whip back and forth to a much greater extent than the rigid roof frame. W ithout a well-designed and connected roof frame there is a very real danger o f collapse. An added complication is the non-uniform ity in the thickness o f the plaster skins. The thickness should be assumed to be uniform ly the least thickness o f the plaster. The outer skin's capacity to resist shear loads is lim ited by the shear bond between the straw and the plaster. The bales are usually pinned and there is some shear capacity in the bales and some shear transfer capacity between the bale surfaces and the plaster skins. Therefore the 37 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. straw-bale assembly behaves like a "sandwich panel", the rigid, thin outer concrete columns (the plaster skins) are elastically connected by the straw-bale core. if there is a toad on the piaster skin... f —■ then the straw substrate must be f capable of bracing the skin "colum n" in either direction with at least 5% of that same force, which depends on the bond between the straw and plaster Fig. 27 Bracing o f plastered straw bale skin Straw-bale designers in California have made use o f cement stucco to carry lateral loads. However, stucco is a b rittle material and so there are some reservations about the use o f this material in seismic zones. Once the stucco has cracked, the building is vulnerable to damage from aftershocks. To counter this problems engineers are designing cross bracing tha t runs diagonally from the top to the bottom o f the wall to back up a fu ll o r partial plaster failure. This can be accomplished using lig h t gauge metal straps, polyester packing straps or 38 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. heavy w ire or slender threaded bolts. These diagonal bracing systems need to be designed fo r calculated forces and should be adequately fastened a t the top plate and foundation. ST>rriNfi* W 4" C 0 M U C , SKi mM& rcc*uses E S ttn r tF * * ( N O r T «fTIp) COS'Piwa m n r u N i a t 4th co«sc, 9K IWIN CI 5 " » p)S'rm » S T M J A T rn u t t f fH O VTU TC D l • -L 4™ C 0M R 3C , y { SWOMtSC / b£0|(W . | , T*'— ; - * r l l ' - C ' M ISim) d-3TX IN 6( B A L E S « 4 U B A K fIM S c c Fig. 28 Various wall pinning strategies Since straw is a flexible m aterial, although it is stacked up like bricks, it does not behave like a brick w all. The wall is flexible and fo r stability and alignm ent, it is necessary fo r the bales to be pinned during stacking. Pins are usually scrap steel rebars that are cheap and easy to drive. However, steel is very much stiffe r than the straw and may be structural overkill. Bamboo or wood dowels are acceptable because they are strong enough th a t the weakness o f the jo in t is s till defined by the soft surrounding bales. Bamboo can be a great pinning m aterial fo r a bale wall because it is easy to drive and can be sharpened fo r easy penetration. 39 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 .2 R oof* and Ceilings1 There are several roof types th a t can be used w ith bale structures. They are however, affected by the type o f wall system used in the bale structure. Almost any roof type can be used in in -fill construction but there are more constraints in load-bearing construction. The roof frame and roof plate can contribute significantly to the stability o f a load-bearing structure. Unfortunately most o f the roof structures b u ilt today s till rely on tim ber as the principle building material. The roof design must integrate performance w ith appearance. The structural role o f roofs cannot be compromised and fo r this reason it is very im portant to spend adequate tim e in designing roofs to provide shade, adequate drainage o f water and protection against the wind. When designing, passive solar requirements can also be considered, open roof faces should face due south fo r maximum solar exposure and should have sufficient overhangs to protect south facing windows from the summer sun. 4.2.1 Traditional Roof Types There are several roof designs: • The Hip Roof: This design is preferred for load-bearing buildings because it distributes load to all four walls (though not necessarily evenly) although it can also be used fo r non load-bearing construction. Another great advantage o f this roof type is that it is less affected by winds than other roof shapes. I t can be b u ilt w ith good-sized overhangs, which help protect the bale walls horn weathering and can extend over porches or garages. On long rectangular structures w ith hip roofs, the central part o f the roof can use trusses. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 29 Vented hip roof, Kate Brown's load-bearing pottery studio, San Lor enzo, New Mexi co • The Pyramid Roof: The pyramid roof is a pure hip roof w ithout the ridge and it distributes w eight equally on all four walls. • The Gable Roof: This roof provides the added advantage o f allowing the incorporation o f lo ft space and o f added solar gain when windows are placed in the south end o f the roof. The gable roof distributes load onto tw o walls. Fig. 30 Gable roof on Joan Chandler’s house, G i l a, New M exi co Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. • The Shed Roof: Shed roofs slope in ju s t one direction. They are the simplest roof to construct and are relatively economical. This is a good choice fo r a simple structure when the builders don't have much experience. A disadvantage o f this roof type is th a t it provides little space fo r roof insulation and venting when using rafters and so simple trusses or truss joists may be required to provide a deeper pocket fo r better insulation. Precautions should be taken when using this roof type in load-bearing walls because the different wall heights do not allow a continuous roof plate to be accommodated. Thrust from the rafters during construction against the lower load-bearing wall can cause it to lean out. A little bracing should be required, if necessary, to keep the wall straight. Fig. 31 Shed roof, B ill and Athena Steen's guest house, Canet o, Ar i zona 42 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. • The Clerestory Roof: These are basically tw o shed roofs combined, one higher than the other and sloping back and the other sloping in fro n t to accommodate windows in the space between. This roof type is usually used in solar designed structures. They allow heat gain and lig h t to enter rooms a t the rear o f the house. Fig. 32 Clerestory roof a t Seeds o f Change Farm, Gila, New M exi co • Flat Roofs and Parapets: Flat roofs are not tru ly fla t but have a slight slope. They need to be detailed carefully to ensure proper drainage o f w ater and avoid leakage problems. Traditionally, the fla t roofs o f Pueblo Indian cultures used peeled tree trunks fo r beams laid across their tops fo r ceilings w ith m ultiple layers o f day-based d irt on them. The top layer o f d irt usually grew grass and such roofs were heavy, required large beams and usually had leakage problems under extended periods o f rainfall. However, they were therm ally efficient and used minimal resources and provided additional space fo r food drying and sim ilar activities. 43 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A modem version o f this roof type in Mexico incorporates a layer o f roofing paper on top o f the ceiling m aterial before the d irt is placed. • Soil cement is sometimes used in place o f plain d irt and sometimes plastered. Flat roofs often have short parapets on two, three or all sides o f the roof. A potential trouble spot for these roofs is where roof drains are used to drain w ater from the roofs and away from the walls. The roof drains go through the roof and so there m ight be a potential leakage point where the roof, parapet and drain meet. One solution would be to have parapets on three sides and the drain on the fourth, although this is not a very effective one and could lead to sheeting on the surface o f the building. Classical treatm ent o f water drainage problems fo r fla t roofs involves the use o f scuppers. These are placed a t the jo in t between the parapet and the roof slab and must be used as a single piece w ithout any jo in ts. Scuppers usually drain water well away from the face o f the building and must be placed below the roofing material. Fig. 33 Modem Puebto-style fla t roof, Catherine W ell's Studio, nort hern New M exi co 44 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. • The Living Roof: This roof can be finished w ith a simple grass covering or can be developed into a complex garden w ith plants, flow ers or edible fruits growing on i t Straw can be used as a base fo r the compost th a t w ill be formed to support the plants and flowers. • A waterproof membrane needs to be laid between the decking and the vegetation; various polymer-based modified bitumen membranes such as P V C are usually used. On large roofs the bales are laid fla t with a gap o f about three to four feet a t the edge. This gap is filled in w ith flakes o f straw. The binding strings on the bales are cut so th a t they w ill begin to break down. After a few months the straw begins to stabilize and hold the minimal amount o f humidity necessary to support the plants. A t this point the compost o r manure can be spread over the roof and plant o r flow er seeds sown. I t may take a year before plants or fruits begin to grow. When constructing living roofs, waterproofing is a key issue and needs careful consideration and detailing to ensure th a t there is no danger o f w ater leakage through the roof to the slab on the interior. Fig. 34 Bales being placed fo r a living roof, Quebec; Canada 45 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.2-2 PQ T P Q S Building domes from straw-bales is a challenging proposal, which requires overcoming several problems. One d ifficulty is the shape and size o f the bales themselves. Masonry domes use smaller bricks, which can be adjusted to create a variety o f curved shapes. Laying bales in a dome shape creates large rectangular voids between the bales. These voids can be filled w ith day-coated loose straw or other m aterial. Also, since bales compress care should be taken when using a structural dome design because o f the potential for collapse. Several experimental dome structures have already been b uilt. Bill and Athena Steen constructed a temporary straw-bale dome in Canelo in Arizona using bales structurally w ithout any supporting framework. The dome was 15 feet in diam eter and was constructed by corbelling (insetting) each course o f bales from the bales in the preceding course. In order to dose the dome, in the upper courses the bales were slightly tilte d inward by shoving flakes o f straw under the bales a t their outer edges. The bales were tilte d only slightly, otherwise it proved d ifficu lt to position the bales and keep them in place. It is im portant to realize th a t this method o f construction relies predominantly on the compressive nature o f the bales. Any gap or loose packing could cause settlem ent and finally collapse. Domes can also be b u ilt using a double structural framework o f bamboo, pipe or flexible poles covered w ith a weatherproof skin w ith the space in between can be filled w ith bags o f straw or bales fo r insulation. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 35 Experimental straw bale dome in C aneh, Ari zona 4.2.3 Vaults The three main challenges in straw-bale vault design are: • Restraining outward thrust • Supporting dead load • Resisting live loads In April 1996, the University o f Oregon sponsored the building o f a 14 x 16 garden storage vault. The vault was constructed using paired ribs as stiffeners. This vault also had "s lit windows" - 12 inch wide frameiess openings spanned by bales. The ribs were placed about tw o feet apart along the wall on the inside and outside and cinched through the bale wall w ith baling twine. There were six paired ribs along the length. To compare the performance, the firs t three ribs comprised o f wood l-by-3s and #3 rebars fo r the other three ribs. 47 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The wood ribs were screwed to the foundation and the rebar ribs were wired to rebar stakes, which had been driven tw o feet into the ground. At the top, the wood ribs were screwed to the ridge box beam and the rebars bent and hooked into the ridge box beam. The interior ribs were laid over falsework o f three frames with horizontal purlins. This provided support and shape fo r the bales as they were laid. Wedges placed between each course tilte d the bales inward to follow the curved shape. The #3 rebars performed nearly as well as the wood, were cheaper and more widely available. The Joints were stuffed w ith well-compacted loose straw, the ribs tied together and the falsework removed. The vault only settled one inch. Fig. 36 Left: An experimental straw bale vault house Right: Experimental Strawbale vault designed and b u ilt by Dan Smith and Bob Theis o f Berkeley, California 48 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 37 Shear mechanism developed by David Mar fo r compression struts in a vaulted straw bale wall assembly 4.3 W all Finishes Bale walls can be finished w ith a variety o f plasters, which add warmth and color to the structure. The plastering process can be one o f the most satisfying experiences o f building a bale structure. In addition to aesthetics, the choice o f plaster is also influenced by the need to finish the bale walls w ith a "breathable” material to allow escape o f any trapped moisture. Selecting a plaster w ill also depend on the desired hardness, the level o f maintenance and the texture and feel. Most cement plasters minimize maintenance but sacrifice other qualities like feel and texture. Soft plasters like earth and gypsum are pleasing to touch and feel, easy to repair, easy to nail and have good acoustics but are not as easy to dean as some harder plasters. 49 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Plaster can be finished smooth, rough or textured and especially soft plasters can be easily textured to create a variety o f beautiful patterns. Plaster is one area o f straw-bale construction th a t m ight cost more and use more material than is necessary in conventional structures. Filling any cavities in the wall ahead o f tim e w ith a mix o f mud and straw also helps to reduce the amount o f plaster needed. However, the advantages o f plaster fa r outweigh the added cost. Plaster adds significant structural strength to a load-bearing bale w all, especially when the plaster is sprayed on pushing it into all the cavities. Plaster also adds thermal mass to a building and coupled w ith the insulating properties o f straw-bales can result in fairly constant internal temperatures w ithout the need for mechanical heating or cooling. Plaster can be applied to a bale wall w ith or w ithout the use o f stucco netting or reinforcing wire. Stucco netting provides a mechanical connection for the plaster, which some plasters need in order to adhere well to the w all. Netting also helps to reinforce cement based plasters and when firm ly attached to the roof plate and foundation can greatly increase the strength o f the structure as a whole. However, stucco netting is b rittle and rigid whereas straw is flexible and so a combination o f the two materials may lead to problems o f incom patibility. A very im portant point to remember in plastering load-bearing walls is th a t the bales must be allowed to reach maximum settlement before plaster is applied unless the bale w all has been pre-compressed. Plasters can be divided into four categories: 4.3.1 Cement Stucco Cement is one o f the hardest plasters. It bonds very well w ith the straw, is very durable and weather-resistant. The mix should not be too rich in cement, otherwise the wall w ill be susceptible to shrinkage cracks. The plastered wall should be covered with a damp doth fo r 50 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the firs t few days to obtain greater strength and reduce the possibilities o f shrinkage especially in hot, dry weather. Cement stucco generally cures in th irty days. Cement plasters are readily available and low in cost and has the added advantage o f being the only exterior plaster recognized by building code. However, it has the disadvantage o f having high embodied energy. I t is made from ground limestone, day, alumina, and other minerals th a t are heated together in a kiln and ground to create a powder. The mining and burning o f cement absorb large amounts o f energy and may not be the best option fo r people who w ant to build with minimum impact on the environment. 4.3.2 Lime Plasters Since the introduction o f cement plasters, lime plasters have fallen out o f use. Lime plaster is durable and porous and evaporates moisture. Lime plaster is one o f the most breathable finishes available, allowing air and moisture to pass through it. It does not have the same kind o f water resistance as cement plaster but it inhibits the growth o f mold, mildew and repels many insects. It is very workable and easier to trowel than cement plaster. I t can be beautifully finished w ith soft matte washed-on colors. However, lime plasters take a long while to set and longer to cure, which is one o f the reasons fo r the popularity o f cement plasters. Lime is widely available and costs about the same as bagged cement. Properly applied lime plasters are very long lasting and as cracks appear, it is possible to repair them by rubbing in fresh lime putty. Commercially manufactured lime takes more energy to manufacture than cement because the production o f quicklime requires significant energy to bum the limestone. However, limestone is easily available and when produced on a small scale can be relatively sustainable. Environmental problems associated w ith lime plaster usually apply to large-scale manufacture. 51 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4,3.3. Clav o r Earth based Plasters Earth and straw have been combined as building materials fo r as long as one can remember. The natural affinity between these two materials makes this an excellent material fo r plastering bale walls. They are made using local soil th a t has a natural balance o f sand to day. Earth plasters are highly breathable and can be both durable and beautiful. Earth plasters can be highly finished as well as easily textured. The main disadvantage is th a t when w ater is added to hardened clay plasters they soften and can erode. This could present a problem where driving rains or snow can be expected regularly and in this case perhaps some natural or chemical stabilizers can be used to prevent erosion. This type o f plaster also may require fairly frequent repair or replacement, which may not be suitable to modem contractor schedules. I t is very easy to apply and is usually applied straight onto the bale surface because o f the excellent bond it forms w ith the straw. It has the added advantage o f being environmentally friendly, and requires very little energy to produce. Earth plasters usually blend very well w ith the curves and bumps in straw-bale walls. Earthen plasters dry w ith a softer feel than cement and can be blended w ith other natural materials like stones and pebbles. Sculpting and relief work is also possible with earth plasters. 4.3.4 Gypsum Plasters These plasters are used on the interior o f bale walls since exposure to rain w ill cause rapid deterioration. As an indoor plaster, it is extremely durable and long lasting w ith little required maintenance. Gypsum plaster is easy to work w ith and soft to the touch sets quickly and is porous and breathable. They are likely to be the most expensive option, especially if used directly from the bag w ithout addition o f any sand. Most supply stores 52 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. keep gypsum piaster, which is recognized by building code. I t adheres well to bare straw surfaces and looks good if allowed to take the shape o f the bales beneath. Gypsum must be mined and heated like cement but the process requires only about one-third o f the energy. The plaster provides a soft finish and takes regular paints very w ell. 4 .4 Openings Doors and windows in bale walls play a very im portant part in defining the character o f the w all. The thick walls present several different options fo r developing openings - they can be used as alcoves, social spaces, fo r seating and fo r displaying small knick knacks in contrast to openings in conventional walls, which are merely openings. Windows and doors in load- bearing assemblies require careful thought and design because the roof load bears directly on the wall sections, which door and window frames. In non load-bearing assemblies, the restrictions are much fewer because the roof load is borne by a rigid assembly other than the bales and so door and window bucks (rough frames) are required to pick up only the weight o f the bales above. When bale walls are stacked and pinned, a fabric is created, which is strongest when it has not been punctured w ith openings. Skylights w ill not affect the stiffness o r strength o f the fabric, but the size and positions o f doors and windows w ill. As a general rule, the total area o f openings in a bale assembly should not exceed fifty percent o f the total wall area. Another general rule is th a t openings should not be placed closer than one and half bale lengths to any comer or any other opening. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 38 Left: Window seat Right: Rounded window opening w ith transom vent above 4.4.1 Openings in load-bearing walls In this type o f wall assembly, the greatest challenge is to ensure fa irly even absorption and distribution o f load by all parts o f the wall to the foundation. There are a number o f ways o f dealing w ith this. The early Nebraska settlers used wooden lintels to span openings. Walls usually contained a few small openings, which were spanned by short headers. This caused minimal disruption to the wall. When a wall is made entirely o f bales it w ill tend to compress evenly under roof loads. However, when there are openings in it, the amount o f compression around the opening varies from other parts o f the w all. The tendency toward unequal settlem ent increases w ith the increase in the number and size o f such openings. The Nebraska settlers preferred to use fewer openings, which were kept narrow. The amount o f lig h t entering a space could be increased by increasing the height o f the windows; this would allow fo r greater lig h t penetration into the room while keeping the spanning elem ent relatively small. 54 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. stuff with straw for insulation if load requires, add center stud' 2" X 4" [5 X 1 0 on]- plywood orOSB holes for foundation bolts^Jfc^ pressure-treated lumber i f on concrete Fig. 39 Box beam doorframe Modem builders use rigid roof plates, metal lintels o r structural frames. The most efficient and easiest approach would be to use a rigid roof plate capable o f spanning large openings, elim inating the need fo r lintels o r cumbersome structural frames. I f the rigid plate bears the roof load, it becomes much easier to design the door and window bucks, which don't have to carry any load. The box beam roof plate is usually capable o f spanning about ten feet! The m ost common approach to door and window openings in load-bearing walls has been to use a steel ladder-type lintel, originally suggested by David Bainbridge, to span the openings. When lintels are used, the combined live and dead load from the roof is distributed through the lintel to the bales on either side o f the opening. These loads are in addition to the normal loads being carried by the bales, so they carry significantly more load 55 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. than other bales and problems may develop. Because straw is a compressible m aterial, the bales under the lintels w ill tend to compress more than other bales causing uneven settlem ent Fig. 40 Ladder-type steel lintel This may cause the roof lintel to dip or the wall finish to crack. Live loads such as heavy winds o r snow loads would aggravate this problem. I t is therefore, wise to avoid using lintels fo r very wide openings. The concentration o f point loads where they bear on the bales increases as the span increases. The lintel should be tw ice as wide as the width o f the opening and should extend a t least tw o feet on either side o f the opening. They should be strong enough to avoid sagging, yet not very heavy. Window and door bucks below lintels should be designed to allow fo r the compression th a t w ill occur on either side o f the opening. Otherwise the lintel w ill exert pressure directly on the rigid window buck. Possibly deforming it and creating problems o f differential settling in walls. Another option would be to place window bucks in th e ir openings after compression has occurred. The bucks can 56 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. then be correctly sized to fit into the openings. One disadvantage o f this method is th a t it is harder to Keep the bales even around the opening. When fu ll settlem ent has occurred and the bucks are finally placed, the bales w ill have to be trimmed and the gaps fille d w ith loose straw where the buck does not fit. 4.4.2 Openings in non load-bearing walls Window and doorframes used in non load-bearing walls do not present the same challenges as those in load-bearing walls. The main design issue is how to secure the frame w ithin the wall section. The sim plest method to use in small openings is to set a rough sawn buck made from 2-by-8s into the wall and to secure it w ith wooden dowels driven through the bucks into the adjoining bales. For large doors and windows, bucks are sometimes attached to structural posts. These frames are uncomplicated and rely on the posts fo r stability and support. tvpical 2“ X 2* X 3/16’ [5 X 5 X 0 5 cm] angle iron; metal straps 2‘ X 3/16' anglc-iron lintel pxw2L— ; — / I . _ \> A / j ; overhang “ 1/2 the width o f opening w ith 24’ [61 cm] minimum > I ” 12’ [30 cm] ^ rebar peg above and below leave gap to accomodate settling 2" X 10-12* [5 X 2S-30 cm’ Ontion: 2* X 4" [$ X 10 cm] / QpUSfl metal bolted to foundation j btaekei/ang|e-iron Concrete, above-ground collar as toe-up Fig. 41 Non-Load bearing door frame and Lintel expanded metal lath i 57 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 .5 Foundations The foundation o f a building provides a rigid base fo r the structure to sit on and must be designed to withstand frost, winds and roof loads. Foundation design is dependent on the local conditions and the specifics o f the structure to be supported. Local factors, which also affect foundation design, indude load-bearing capacity o f the soil, soil type, depth o f frost line and w ater table, slope drainage and wind and seismic conditions. The bottom o f a bale wall must be separated from the foundation. Minimal precautions should a t least indude a waterproof barrier laid over the supporting concrete surface to halt any moisture getting into the bales through capillary action. Additionally many builders lay a one-inch pea gravel layer between 2 by 4 plates along the inside and outside w all faces, ensuring that the bales never sit in water. Fig. 42 Straw bale wall footing w ith moisture proofing Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Foundations can be o f three basic styles: 4.5.1 Slab-on-Grade Foundations A slab-on-grade foundation is a continuous cement pad that is designed to flo a t on the grade surface. Excavation is minimal - only the topsoil needs to be removed. Slab foundations are not anchored to the soil below the fro st line in any way. In climates where frost is a concern, slab foundations use an insulation blanket around the perim eter o f the foundation to prevent fro st penetration into the soil below the slab. For perim eter insulation, the general rule is th a t six inches o f insulation is required fo r every fo o t o f fro st penetration. The insulation needs to be designed specifically fo r below grade applications. Insulating the foundation helps take fu ll advantage o f bale walls. Uninsulated foundations can account for as much as seventeen percent o f the total heat loss o f a building. Slab foundations are usually inexpensive and require minimal form work. They can be finished in several ways; the concrete can be le ft bare or it can be color tinted or stained. Tiles, linoleum or carpet can be laid directly on the cement. If a wood floor is required, it w ill have to be separated from the cement by a system o f spacers. SUb-otc-gnule, uritlvelectricjd' plum jfuuj Fig. 43 A typical slab-on-grade foundation incorporates thicker concrete around the perim eter and an insulation blanket to prevent fro st penetrating the soil beneath 59 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.5.2 Perimeter Walls Perimeter walls usually extend the vertical walls down to a secure footing below the frost line. They are often used to create a below-grade basement but can also be used to create a strong foundation w ithout a basement They are generally made o f poured concrete or mortared concrete block. Provisions fo r drainage are made a t the base o f the foundation. This is the most expensive foundation option because o f the depth o f excavation required and because o f the specialized equipment needed. Extra m aterial is required fo r the foundation, insulation and perim eter walls but the payback is the additional storage space and the strength o f this type o f foundation. A cheaper and faster alternative to a concrete perim eter wall is a rubble trench. The excavation is filled w ith various sized stones and compacted to avoid future settling. The outside end o f the trench is insulated and a concrete curb is poured on top o f the stone a t grade level to provide a fla t surface to stack the bales. Fig. 44 Perimeter wall foundations often incorporate fu ll basements, as shown. The same footing and wall can be used w ithout a foundation Bdumut t F o u K i U t u n , WaJ l Shot ui K^ • [ Hr t i t nn, of s o i l • n u t u u v t f unt uy pi f ‘ d n u tu y*U yt r • dAm p-j t nef uy • iv ittk o m vtU w S t *bov*gnd* 60 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.5.3 Pier Foundations These foundations are used to raise a building above grade level. The building rests on a wooden framework supported by piers and the piers themselves rest on footings below the frost line. Piers can be wooden posts - usually treated to protect them from ground moisture, poured concrete piers, stacked concrete blocks o r perhaps tire or rammed earth piers. Piers should rest on wide footings. These are relatively very cheap foundation options because a minimum o f excavation is required and no below-grade insulation needs to be provided. The biggest drawback to this kind o f foundation is th a t in cold climates, the water feed pipe w ill be exposed to freezing temperatures in the a ir and ground. To keep from bursting, different strategies such as heated pipe wraps, drain-down systems and pressurized bladder pipes are needed. A wooden-framed flo o r system, topped with a plywood sub-floor is most commonly used w ith pier foundations. Fig. 45 Pier foundations can use concrete o r wooden piers to support a floor framework 1 At h e n a Swent z el l St een; Bil l St een; Da v id Ba inb r idge wi th D a v i d B s e n b e rg ; The St raw B a le H m o- C hels ea Gr een Pub lis h in g C o m p a n y, Whi te River J unc t ion, Ver mont ; pp. 152-163 k! i Cc nj w tte , Pier FoiutatioK, 61 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5. ADVANTAGES OF STRAWBALES 5 .1 Sustainability The official definition o f "sustainability", which comes from the 1987 report o f the International Commission on Environment and Development, states th a t " Human ki n d has t h e a b i l i ty to achi eve sust ai nabl e d e ve l o p m en t . . . t o m eet t he needs o f t h e M u re w i th o u t com pr om i si ng d i e a b i l i ty o f fu t u re generat i ons to m eet th e i r own needs. " Sustainable refers to a system th a t can be perpetuated forever. Unlike tim ber, straw can be grown in less than a year in a completely sustainable production system. Straw can be successfully intercropped with other valuable crops, increasing the value and productivity o f the land. In China, wheat is successfully grown w ith highly valued fru it producing jujube trees. I f large crops o f straw are removed from a field every year, the use o f soil amendments or crop rotations may be required to maintain soil fe rtility and health. If perennial crops are used, however, the need fo r such measures is reduced and erosion and run-off can also be avoided. The conversion o f straw into a renewable resource is particularly useful in areas where there is a scarcity o f tim ber such as the steppes o f Russia. Here straw is plentiful. Straw bale construction is also ideal fo r desert areas where w inter wheat is grown along rivers. Hence there is little doubt that the abundance o f straw and the ability to replenish it makes it a sustainable resource w ith significant potential in the building industry. 5 .2 A vailability Straw is grown in almost all parts o f North America and is in plentiful supply in countries like China and Russia. Straw bale structures can be found almost all over the US. According to 62 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Environmental Building News, over 140 m illion tons o f straw is produced in North America alone. I f we were to assume that 25 percent o f this could be used w ithout harming the soil, we have a ready resource o f about 35 m illion tons. I f this were all used to construct exterior straw bale walls, 2.7 m illion, 1000 square foot, single-story buildings could be b u ilt each year! This is a staggering amount. B ot h Hi st or i cal (pre 1940) and C o n te m p o ra r y Fig. 46 Locations o f straw bale buildings in the US in 1995 1 Area Grain Yield ! • X Straw Yield Total N.A. Harvested In d ex Straw Prod. Grain (m il. acres) (m il. ha) (Bu./ acre) (tons/ acre) (tonnes/ ha) (tons/ acre) (tonnes/ ha) (m il. Tons) (m il. Tonnes) B H H H 59.7 24.1 35.7 1.1 2.4 0.4 1.3 2.9 76.6 69.5 [ 1 ■ M l 30.6 12.4 32.7 1 i 2.2 0.4 1.2 2.6 36.1 32.7 i . . . ~ . . . . . . i i 2.7 1.1 2.8 6.3 0.45 2.7 6.1 7.4 6.7 Table 3‘ North American Straw Production 63 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. jn tiB riH i 0.5 0.2 26.7 0.7 1.7 0.28 1.5 3.5 0.8 0.7 A ffiH S M 0.4 0.2 31.6 0.9 2 0.28 1.8 4.1 0.7 0.7 1 1 6 2.4 51.7 0.8 1.9 0.4 1 2.2 6 5.4 g g jg g g i 3.3 1.3 73.9 1.2 2.7 0.4 1.4 3.2 4.7 4.3 8.4 3.4 50.1 1.2 2.7 0.47 1.1 2.4 9.1 8.2 1 1 M g H 10.1 4.1 53.7 1.3 2.9 0.47 1.2 2.6 11.7 10.6 Total 121.7 49.2 141.3 128.2 Table 3‘ contd. North American Straw Production 5 .3 Pollution Reduction - Innovative Use o f a W aste Product Because o f its high silica content and long stems, straw does not easily decompose and poses a disposal problem fo r most farmers. In California, fo r example, a m illion tons o f rice straw is burned each fa ll and the fires create a pall o f smoke over the Sacramento valley for several weeks. Field burning also emits carbon monoxide, methane and methyl bromide, greenhouse gasses, which are responsible fo r global warming. Annual straw burning in California produces more carbon monoxide and particulate than all o f the electric-power generating plants in the state combined. The a ir pollution has caused the state's Air Resources Board to initia te the process o f banning the burning o f straw. Rice Straw 1 m illion 56.000 W heat Straw 97,000 5.000 Power plants 25.000 Table 4" Annual Carbon Monoxide Production from Power Plants and Straw Burning (in tons) 64 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 .4 Low Embodied Energy There are several reasons why people are attracted to straw bales as a building m aterial. One o f the main reasons is th at building w ith bales provides the potential fo r building a "low im pact" home. Embodied energy can be defined as the energy tha t goes into the production o f a m aterial. I t is often a hidden cost th a t is overlooked. I t is becoming more common to compare the environmental benefits o f materials by comparing their embodied energy. Table 5 below shows the embodied energy o f straw as an insulation material compared to an equivalent amount o f other insulation materials. For these calculations, several assumptions were made: • The bales are wheat straw bales, which yields about 40-50 bales per acre in Minnesota. The lower yield value was used. • The average two-string bale would have an insulation value o f approximately R-43* Straw Bales 662 Blown Cellulose 3.075 Fiberqlass Batts 23.319 Mineral Wool 15,272 Expanded Polystyrene 92,250 Polyisocyanurate 73.288 Table 5 " v Embodied Energy in Various Wall Insulation Materials (4 // val ues are based on t he m a t e ri a l t hi ckness th a t achi eves an R -vai ue equi val ent to t h e aver age 2 -st ri n g st raw bal e, o r R -43. 2) As Table 5 shows, the embodied energy fo r straw bales is lower than fo r any other insulation materials. In fact it is over one hundred times less than the embodied energy o f the synthetic foam insulation. There are o f course several other considerations such as the use o f steel rebars to pin bales. Steel is very high in embodied energy and so reduces the 65 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. environmental benefits o f using bales. One must also consider what happens to this energy comparison if the bales need to be shipped from another location. S.SCOTt The cost savings realized in a straw bale building depend very much on the method in which construction is undertaken, the clim ate, the region and the site. In some parts o f California, permits and fees can cost more than a small straw bale house. A good way to begin evaluating the cost o f a bale building is to compare its cost w ith th a t o f a sim ilar sized building built w ith a different wall m aterial. The cost o f building a house w ith bales increases w ith other considerations such as using adobe, super-insulated frame construction etc. Wall systems typically represent a maximum o f 21% o f the total costs o f home construction and only owner-built straw bale construction has showed a real saving in costs. A 2-by-6 frame structure w ith R-19 walls can be b u ilt fo r almost the same price as an identical straw bale structure w ith R-42. The difference is th a t the one bu ilt w ith bales is fa r superior in terms o f energy efficiency, durability, com fort and aesthetic character. Another way o f looking a t cost is the price paid per bale. Straw, which is grown and baled w ithin the immediate area o f the site, w ill greatly reduce the cost o f the bale. The cost o f bales is also influenced by the problems o f disposal, the amount bought a t one tim e and the distance to which the bales need to be transported. The greatest advantage o f bale construction is th a t it provides opportunity fo r community interaction and having workshops where friends and fam ily help w ith the construction can greatly reduce costs. The primary reason fo r this is the ease w ith which the wails can be assembled. The type o f home or structure w ill also greatly affect the cost o f the building. The greater the com plexity, the 66 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. higher the costs because the technology required may not allow a great deal o f owner participation. Very Low: 120-1000 sq. ft @ costs o f $5-$20/sf a. scavenging, salvaging materials b. m aterial costs only-owner builder labor throughout c. initia l start-up costs, ongoing improvements-pay as you go d. Nebraska style, tim ber frame, and post and beam_____________________ Low: 1000-1500 sq. ft < § > costs $30-$50/sf a. contractor b u ilt - owner builder walls, finishes b. sub-contract foundations, plumbing, mechanical, roof c. experienced job-site supervisor d. materials a t m arket cost e. typically post and beam or Nebraska style____________________________ M oderate: 1500-2500 sq. ft @ costs $50-$80/sf a. standard contractor built home b. production housing c. speculative development d. typically frame w/wrap-around. post and beam________________________ H igh: 2500-4000 sq. ft @ costs $80-$120/sf a. luxury homes b. custom design c. site-specific d. m arginally less than conventional construction e. typically post and beam o f frame w/custom features___________________ Table 6* Outline Range o f Straw-Bale Construction Costs per Square Foot (sf) When bale buildings are b u ilt with precautions and w ell maintained, they can last fo r very long periods o f tim e. Life cycle costs measure the construction, financing and energy costs over the entire life o f a building. Opportunities fo r cost savings through reduced energy costs apply most directly to owner-builders and owner-occupants. These savings accrue incrementally over the years and so immediate savings are not recognized. Thus speculators have little financial incentive to invest in straw bale buildings because there is no product to patent or sell. The benefits o f straw bale structures are not derived from buying, selling or building it but from living in it. 67 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Construction cost 134,000 134,000 93,000 73,700 Down Payment (20% ) 26,800 26,800 18,760 14,740 Finance - 30 year fixed rate a t 8% 175,969 175,969 123,179 96,783 Energy use at 1993 energy costs 30,000 18,000 18,000 4,500 Total life cyde costs 366,769 354,769 362,079 264,375 Savings over conventional construction 12,000 113,830 177,046 Table 7 "' Life cyde costs (a ll figures in $US dollars) 5 .6 Insulating Properties The insulating properties o f a m aterial are defined by its R-value, the resistance to heat flow . The R-value o f wood is 1 per inch, brick is 0.2, and fiberglass batts are 3.0. The higher the R-value, the better the insulation. Straw bales have significantly higher R-values than conventional building materials - about 2-3 times better than the wall systems o f most well insulated homes. Additionally, the mass gained from the plastering walls can greatly improve the overall thermal performance o f a bale wall assembly. The superior insulating properties o f straw bales also provide great potential fo r energy savings when combined w ith other systems such as solar cells or photovoltaic assemblies. 68 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. This inherent characteristic o f straw bales also makes passive cooling systems such as cool pool or cooling towers, more practical and efficient fo r homeowners in very hot, arid areas. This saves on the costs o f installing expensive heating and cooling equipment. To get the most benefit from highly efficient straw bale buildings, the building should include a w ell- insulated a ttic o r roof, good perim eter foundation insulation, well insulated openings and proper sealing to minimize infiltration. The walls should have a breathable finish, which allows optimum ventilation through the walls. Building walls w ith straw is much less labor intensive and less daunting than building w ith concrete, brick o r stone and requires considerably less skill and technical knowledge. There is room fo r individuality and creativity, which ultim ately leads to energy efficient and unique buildings. Building w ith bales also allows room fo r error, enabling ordinary folk w ith little or no building experience to participate in building their own homes. Building w ith conventional building materials instills fear and apprehension in most people because o f the prohibitive costs, complexity and high level o f technical skill required. In straw bale building, the whole process is more relaxed and fun, allowing even children to participate. The idea is to learn how to build and to enjoy doing this! It has been demonstrated in the United States that the basics o f bale building can be learned in a tw o- day workshop. 1 Re pr i nt ed f r om Trie Last St r aw. I ssue No. I I , S u m m e r 1995, wi th per mi ssi on f r om E nvir onmen t a l B ui ld in g Ne ws , vol . 4, no. 3, Title: Trie Next Gr eat B u ild in g Mat er ial “ So u rc e : Cal i forni a Agri cul tural Magazine, Vol . 45, no . 4 ( July- August 1991) 1 1 1 Mc C ab e , Joe. 1993. Trie Ther mal Resist ivity of St r aw B ai es for Cons t r uc t ion. MS . Thesi s, Dept Nudear Engr. , Uni v. of A r izona 69 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I V B rid ge s, T.C and E. M. Smith. 1979. A m et ho d for det er mi ni ng the total ener gy input for agri cul t ural pract i ces. Trans. A S A E , 22:781-784 v Wil s on, Alex . 1995 I nsul at i on mat er ials: env i r onme nt al comp a ri s o n s . Env ir o n me n ta l B u ildin g Ne w s ” Pr ices not incl uding land c o s t s , si t e dev e l opme nt , or utility i nterface. C om piled wi t h data f r om Hof f mei st er, Ke mb l e , Ma c Dona ld, Pe r r y a nd Myhrman v u E d it e d b y Ly nn e Eli za bet h a nd Cassandra Ad a m s; Al ternati ve Cons t r uc t ion - c o n t e m p o r a r y N a t u r al B u i l d in g M e t h o d s : Joh n Wil e y & S o n s , Inc pp. 226 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6. PRECAUTIONS AND DISADVANTAGES C . 1 M o ir tv re Water is a potential hazard, not ju s t w ith straw but w ith any building m aterial. Wood, brick and even concrete w ill decompose when exposed consistently to moisture. Bales must be kept as dry as possible from the tim e they arrive on the site through out the life o f the building. W et straw molds and eventually decomposes, creating an unpleasant odor, potentially harmful spores and possible structural failure. 6.1.1 W ater and Straw - The Capillary Mechanism Although wood and straw are both sim ilar in organic composition, they vary considerably in structure, mass, density and surface area, and consequently react very differently to moisture. There is a great deal o f variation in the way th a t moisture enters, leaves and travels inside a bale wall. Bale walls are made up o f m illions o f individual straws th a t can absorb and dispel relatively large quantities o f moisture. Compared to wood fiber, straw is loose and provides greater opportunity fo r capillary movement and moisture retention. Straw is also less dense and porous than is wood and therefore more readily available fo r moisture transport and storage. This tendency o f bales to absorb and dispel moisture works to protect the interior o f the wall from high moisture concentrations th a t would otherwise support fungal growth. The moisture absorbed by the straw is usually stored over the very great surface area o f the straw and then dispelled through the stucco when conditions permit. This enables a bale wall to dry to the outside relatively quickly and efficiently. Problems usually occur when this great quantity o f moisture gets trapped w ithin the wall and is unable to escape. 71 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.1.2 Sources of Moisture Damage Many practices have been developed over the years to help solve key moisture problems and it is advisable to apply these practices to bale construction. Moisture can enter the walls in tw o prim ary ways - through vapor penetration and through direct air leaks. Builders must take both these into consideration in order to adopt adequate precautions. When we warm our houses, we are basically fillin g the house w ith warm moisture-laden air. The house is relatively airtight and the warm a ir contains more moisture than the outside colder a ir. Additional moisture is added through cooking, bathing and other house hold activities. The inside a ir w ill try its very best to get out o f the house and transfer its heat and m oisture to the outside colder air. The warm, m oist a ir th a t travels through the walls does not remain warm and moist. At some point it w ill begin to cool. I f it cools enough, it w ill condense. The point at which this occurs is known as "dew point". I f this liquid is deposited in the wall w ithout any possibility to dry out o r escape, the bales w ill ultim ately rot and develop mold. Moisture can also enter the house through a ir leaks such as cracks, openings and penetrations in the wall. Most testing confirms th a t these sources o f moisture penetration present a much greater risk than does vapor m igration. Most moisture problems occur because o f bad building practices. Straw bale enthusiasts plaster bale walls w ith stucco, bonding it w ith thousands o f wicks o f straw, embedded in it, tig h tly packed and w ith poor drainage. This construction practice is used in coastal areas or regions w ith slanting rains and weak springtim e drying conditions. Most o f the tim e, not enough consideration is given to window detailing, adequate overhangs o r back splash onto the lower bales. 72 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In an occupied house, zones o f damp slowly rotting straw were found under poorly b uilt windowsills, and under inadequate overhangs. Some w ater may have been seeping down from fogging of the indoor glass surface but the te ll tales signs o f water entry were prim arily on the exterior. Conversely, sim ilarly positioned firs t flo or windows seemed very well built w ith tig h t sills over excellent cement-rich stucco, and here the straw under these was dry and sound. In the same w all, bales ju s t above the slab-on-grade floor were found to be damp and slowly rotting. 6.1.3 Wind-Driven Moisture Penetration In temperate dimates, moisture penetration through the building envelope due to wind driven rains poses a great threat to bale structures. This accounts fo r a great deal o f moisture damage and can occur through direct penetration or through capillary suction through the ground. Carefully designed overhangs, sealing o ff all penetration points and control o f all fissures and cracks are essential and cost-effective ways o f preventing the moisture from entering the building envelope. St i ut ds ur t L O vt rf t A H j : g reat er Over hang: P o r c h ? Over hang: L o t t o f ra i n , h i ts undL L e s s re i n , k i ts u rtJ i N o re i n , h i ts w e ll Fig. 47 Simple techniques like increasing roof overhangs on walls exposed to frequent rains can adequately protect the bales from moisture 73 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.1.4 Vaoor Barriers Reducing air leakage is usually the firs t and most effective line o f defense. Special care should be taken to seal pipes, electric outlets and window and door openings. I f vapor and moisture barriers are used, they should be used w ith discretion and care. The introduction o f a sheet barrier inhibits the natural tendency o f the bales to dispel the absorbed moisture. The moisture that travels through the w all is likely to condense a t the barrier interface causing a point o f concentration fo r the moisture w ithin the w all. Condensation usually occurs against such barriers when the sun strikes walls after rain and vaporizes the water between the stucco and straw layers. This vapor moves into the wall and w ill condense into liquid but now cannot escape because o f the presence o f the barrier. Building w ithout a vapor barrier sim plifies the building process, the barrier can in feet even cause some structural problems. The barrier can only be attached to the bales a t the top and bottom making it d ifficu lt to maintain tautness. The vapor barrier also prevents the plaster from adhering directly to the straw. This not only complicates the plastering process, because in most cases more metal reinforcement w ill now be required, but also eliminates the substantial structural benefits that are derived from the strong mechanical bond between the bales and the plaster. I t is essential to remember that bonded together, straw and plaster form a stressed skin panel, which has a greater strength than the sum o f the individual materials. I t is beyond the scope o f this thesis to study vapor m igration. I t suffices to say tha t great care should be taken when making the decision to use vapor barriers, depending on the hum idity levels and the dim atic conditions. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.1.5 Precautions Good straw bale design minimizes the possibility o f moisture penetration but maximizes the potential fo r drying. There are some ground rules and general precautions that are not very cost intensive and can save a great deal o f expense later on. • Adequate overhangs should be provided particularly in areas where driving rain is expected. • Breathable, good quality stucco should be used. It should be tension meshed against shrinkage cracking. • Care should be taken to carefully detail windowsills and openings to minimize a ir infiltration and moisture penetration through them. • A careful foundation detail should be provided where the lowest bale course is sufficiently separated from the footing by a moisture barrier to prevent moisture penetration through capillary action. Bales should be raised about 6 to 8 inches above ground level. • Protect the lower course o f bales against splashes. • Care should be taken to seal all possible a ir leaks through the interior face o f the house. • Maintain a moderate relative hum idity level w ithin the house during winters. Decay fungi grow in straw when it is very w et i.e. above fib e r saturation level, which is typically 27-30% and when temperatures are relatively warm (between 75 F and 90 F). Typically fo r load-bearing construction moisture levels in the bales a t the tim e o f installation should be below 15-20% o f the dry weight o f the bales. This represents a new form o f sick building syndrome, so moisture building must be carefully considered. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 .2 Fire Safety Straw bale walls are naturally fire resistant while loose straw is a great fire hazard. The compact nature o f a bale wall does not contain sufficient a ir to readily support combustion, but it does contain sufficient a ir to have good insulation value. When bale walls are plastered, the already resistant assembly is further encased inside a non-combustible casement. The fire would have to bum through the plaster skin to reach the bales. Loose straw, on the other hand, is the real danger. The large amounts o f loose straw th a t begin appearing a ll over the site when construction begins is usually the real source o f fire . Smoking, welding, grinding or any other activity th a t can produce a spark should not be undertaken in the presence o f loose straw. Loose straw should be kept away from walls to prevent the fire from accidentally spreading to the walls. In regions where there is the possibility o f brush fires, metal roofs, metal soffits and fire resistant window shutters may be a wise choice. In such cases, a fire retardant a t the top o f the wall m ight help to prevent the fire being carried down to the walls through the roof. Fire extinguishers should be kept a t hand and should a bale fire ever occur, it would be advisable to use the extinguishers, rather than water, which may cause further moisture damage. Several tests conducted on bale walls have shown th a t even a t very high temperatures, wood is likely to bum where as the straw is most likely to char and smolder, but not bum. 6 .3 Storage I f stored property, bales can be protected from rains and fire hazards before stacking o f walls has begun. Bales should be kept dry by storing them o ff the ground, preferably on pallets to prevent moisture absorption through the ground. 76 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. They should be covered w ith good quality tarps to protect them against the rain. The tarps should extend down the side o f the stored bales by a t least one bale and should be crowned a t the top to prevent water from collecting there and leaking into the middle o f the stack through pinholes o r tears. Inexpensive tarps and covers are prone to tearing easily and make fo r easy moisture penetration. A good method is to firs t cover the stacks w ith plastic sheeting to provide waterproofing followed by the tarp. Tarps should be secured against strong winds by anchoring their edges to the ground. This can be done by using anything w ith weight such as concrete blocks or old tires tied to the end o f a rope and attached to the eyelets a t the edges o f the tarp. Post and beam structures can be used as storage sheds themselves. I t is advisable to erect the framework and roof so th a t the bales can be protected against rain. This is a great advantage o f in fill bale walls. C.4 Sdnnfc-gctfotnwDaB The ability o f straw to perform in earthquakes is s till under a lo t o f speculation, and several guidelines have been developed and are recommended when constructing in seismic zones. Conventional stone, brick and concrete are extrem ely hazardous in earthquakes and costly to reinforce. In contrast, strawbales have a good height to width ratio and can be reinforced w ith wood, bamboo o r steel. Plastering bale walls adds a great deal o f strength to structures by creating a stressed skin panel. The prim ary loads are now borne by the plaster w ith the secondary system being the strawbales. Bale w alls may actually absorb much o f the shock o f the earthquake, instead o f transferring it to the roof as normally occurs in conventional buildings. Their inherent flexib ility and strength are ideal fo r earthquakes, as long as roof and foundation connections are adequate. 77 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. W ithout some precautions, bale walls could slip o f th e ir foundations. Although the friction between the bales is probably sufficient to keep them in place, the friction between the bottom bale and the footing, where the earthquake forces are very intense, m ight not be sufficient to prevent slippage and subsequent collapse. Similarly, if the rigid roof is not securely tied to the bales, it could slip o ff, causing serious injury and damage. Several methods o f construction have been used to ensure strong and secure connections to roof and footing. One solution is the "key” shown below in the figure. The bale wall can be keyed to the roof and foundation to prevent slippage. To make a key, 2 x 4s are pressure treated and placed length-wise along the inside and outside o f the footing. The bales are notched a t the bottom comers to fit inside the plates. The w eight o f the bales and roof is sufficient to prevent the bales from jum ping over the plates, while the plates prevent the bales from sliding laterally o ff the footing. The roof is keyed sim ilarly by notching the top bales so that the plates are notched into rather than resting on the bales. These plates further contribute to the strength o f the wall by providing a surface to which the plaster lath can be secured. The lath should thoroughly wired through the bales fo r greatest strength. The foundation plates must be securely fastened to the foundation by using commercial hold-downs, which are thoroughly embedded in the foundation. Construction hardware should be used to adequately strap the roof to the top plates. The roof assembly should be fastened to the foundation anchors using w ith threaded rods, cable o r strapping. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. S la b \ ^ — P J ’ T ^ #<r \> V = \W \ ' J r . * 4 M i s n p ^ 2x4- P.T. Top Plates W/Rebar Stakes plaster lathing Attach Top & Bottom, Tie Through Bales 2x4 P.T. Bottom Plates W/J-Bolts into Footing G rade r tE V I 3 ■s-TTTf— i i » /M 'Z T n i'i Fig. 48 Keyed Plates An alternative to the wooden top plates is a concrete bond beam. This could be keyed to the bale by notching into a deep groove created down the center o f the bale and pouring the concrete into the groove. Such a bond beam could also double as a lintel over doors and windows, could contribute to the strength by adding w eight and thereby increasing the friction and could efficiently tie together wood frame walls and bales. Therefore, w ith some precautions, straw bale is a naturally good m aterial fo r building in high seismic zones, its greatest advantage being that it is relatively lightw eight and flexible, enabling it to absorb the vibrations w ithout collapsing. 79 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2x4 Top Platee W / J-Bolts Top Bale Fig. 49 Bond Beam 6 .5 Perm its and Codes Straw bale construction, like any other new (o r rather reinvented) building method has been m et w ith a great deal o f skepticism by both builders as well as building officials. However, great progress has been made, through testing, workshops and public involvement in fam iliarizing building officials w ith the techniques o f straw bale construction. Straw bale structures are b u ilt almost all over the United States and in many parts o f the world including Japan, Mongolia, Canada and Finland ju s t to name a few . In 1993, Matts Myhrman, one o f the pioneers o f strawbale construction began the process o f introducing strawbale construction to building officials in Pima County, Arizona. Together with David Eisenberg o f the Development Center fo r Appropriate Technology (Tucson, AZ), they began a series o f tests and started to compile inform ation to develop a set o f codes fo r strawbale 80 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. construction. Three years later a fte r several tests and meetings, the County o f Pima and City o f Tucson adopted the "Prescriptive Code for Load-Bearing and Non-Load-Bearing Strawbale Construction" as Appendix Chapter 72 o f the local adoption o f the U ni f orm B ui l di ng Code. Before this, there were no specific guidelines to refer to when designing strawbale structures and so building officials in California used Uniform Building Code Section 104 "Alternate Materials, Design or Methods o f Construction" to issue permits fo r such structures. Lack o f general guidelines made it d ifficu lt fo r plan checkers to acquire relevant inform ation and made it very d iffic u lt fo r homeowners and builders to acquire permits. Also, the application o f non-specific design guidelines to strawbale construction sometimes required over designing and leads to and increases in co st Issues o f moisture and the use o f vapor barriers require unique attention and cannot use the same guidelines as applied to other types o f structures. People also began to realize the benefits o f using strawbales and the negative consequences o f burning tons o f strawbale everyday. Some members o f the California Assembly saw th a t it was im portant to remove the regulatory impediments to strawbale construction and in 1995, introduced Assembly Bill 1314 based on the d ra ft code from Pima County. The Bill was passed by the Assembly and Senate and approved by the Governor. In the Fall o f 1995, the B ill was added to the Health and Safety Code as Section 18944.30-35 and 18944.40 (referred to as 18944). I have included a complete copy o f this in the Appendix. Many counties in California have adopted this code and use it to review and issue permits fo r strawbale projects. The H8iS 18944 describes many strawbale details used in construction a t the time when the guidelines were w ritten in 1995. Since then, great progress and new discoveries have been made, hence the code should not be rigidly adhered to but used as a guideline. 81 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. There are currently strawbale codes in the State o f New Mexico; Boulder and Cortez, Colorado; Austin, Texas; Tucson, Tempe, Guadalupe, Pima and Pinal Counties, the phoenix Metropolitan Area in Arizona; and in the State o f California.' 1 Edit e d b y K el ly Lemer a nd P a m e la Wa dswor t h G ood e, The Bu ilding Offi ci al ’s Guide to St r aw- bal e Const r uct ion. Ve r s ion 2.1, ( publi shed b y the Cal i f or ni a St r aw B u ild in g A ss ocia tion © 2000) pp.3-4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7, TESTS ON STRAWBALES 7 .1 Fire In laboratory tests conducted in a t the University o f California’s Richmond Field Station in 1997, a strawbale wall passed the ASTM E-119 test fo r a one-hour fire rated w all. Sim ilar tests conducted in New Mexico showed some charring o f straw where the plaster had cracked and a temperature rise o f only 12 F after tw o hours. Even unplastered strawbales are good fire resistors. In the New Mexico test, it took 34.5 minutes to bum through an unplastered strawbale a t temperatures o f 1500 F. 7.1.1. SHB AGRA. INC E-119 Sma ll Scale Fire Test. New Mexico. 19931 Two separate tests were conducted on an unplastered tw o-string strawbale wall (using 18" thick wheat bales) and the second on a wall panel in which the bale wall was plastered w ith gypsum plaster on the interior (heated) side and cement stucco on the exterior. The tests revealed that the unplastered panels were charred through only 8 o f the 18” thickness after 34 minutes. The maximum temperature recorded on the interior side was 1691 F a t 30 minutes. The plastered bale panel was tested fo r over two hours a t temperatures o f around 1942 F! The temperature rise on the unheated side o f the bale averaged less than 10 F, w ith the peak value being 21 F. The plaster on the heated side cracked and where there were cracks, the strawbales were charred to a depth o f about tw o inches. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TC 10 TC 11 TC 14 TC 16 TC 17 TC 18 (m iddle) (m iddle) (m iddle) 10 1 1 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 49.3 49.4 49.9 49.4 49.3 49.4 49.5 49.6 49.5 49.6 49.6 49.3 49.7 49.7 49.7 49.7 49.7 49.7 49.7 49.7 49.8 49.8 49.9 49.9 50.2 50.1 50.1 50.2 50.3 49.6 49.6 49.7 49.7 49.7 49.7 49.7 49.8 49.7 49.8 49.7 49.8 49.8 50 49.9 49.8 49.9 49.9 50 50 50.1 50.1 50.2 50.2 50.4 50.3 50.3 50.3 50.4 50.2 50.3 50.3 50.3 50.2 50.2 50.1 50.2 50.2 50.1 50.2 50.2 50.2 50.3 50.4 50.3 50.4 50.5 50.5 50.6 50.7 50.7 50.8 50.9 51 51.1 51.3 51.4 51.5 49.3 49.5 49.6 49.7 49.4 49.6 49.6 49.7 49.7 49.7 49.7 49.9 49.8 49.7 49.8 49.8 49.8 49.8 49.9 49.9 49.9 49.9 49.9 50 50 50.1 50 50.1 50.1 50 50 49.8 49.8 49.7 49.8 49.8 50 49.8 50 49.8 49.9 50.1 50.1 50.1 50.2 50.2 50.2 50.3 50.4 50.5 50.6 50.7 50.9 51.1 51.3 51.5 51.9 52.5 49.7 49.7 49.7 49.7 49.8 49.7 49.7 49.8 49.7 49.7 49.7 49.9 49.7 49.7 49.8 49.7 49.8 49.8 50 50 50 50.1 50.3 50.3 50.4 50.5 50.6 50.7 50.8 47.9 47.9 47.9 47.9 47.9 47.9 47.8 47.9 47.9 47.8 47.9 48.5 47.9 48 48 47.9 48 48.1 48.2 48.3 48.5 48.7 48.8 48.8 48.9 49.1 49.2 49.4 49.7 48.1 48.1 48.2 48.2 48.1 48.1 48.2 48.3 48.3 48.2 48.3 48.2 48.3 48.3 48.4 48.4 48.3 48.4 48.4 48.5 48.6 48.7 48.8 49.2 49.5 50.1 50.7 51.5 52.2 49.7 49.7 49.7 49.7 49.6 49.6 49.7 49.7 49.6 49.7 49.7 49.7 49.8 49.8 49.9 50 50 50.1 50.2 50.3 50.3 50.5 50.7 50.9 51.1 51.4 51.6 52.1 52.8 Table 8* Small Scale E-119 Fire Test - Exterior Skin Temperatures 84 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 .2 M oisture Prolonged exposure to moisture is the greatest danger to strawbale walls. W ith continuous exposure to adequate moisture and warmth, the fungi present in bales produce enzymes that break down the cellulose in straw. Fortunately, the moisture content in bales needs to exceed 17 - 20 percent by weight to support fungal growth. 7.2.1 Canada Mortgage and Housing Corporation. Ottawa. Ontario. Canada Moisture testing in plastered bale walls suggests th a t the maintaining the breathability o f the walls may be the most efficient defense against decay. The Canada Mortgage and Housing Corporation (CMHC) is the federal housing agency in Canada responsible fo r policy and research developm ent The research division o f the CM CH has been investigating the ability o f strawbale houses to withstand moisture w ithout rotting. In 1997, the CMCH carried out investigations on the integrity o f several ten to twelve year old strawbale buildings ju s t North o f Ottawa in Ontario, Canada. The stucco on the buildings was broken open and moisture meters inserted into the walls to measure the moisture content. Where the straw had been exposed to frequent w etting, it had rotted and the moisture content was very high at about 40% where the straw was dose to the soil. The straw in these locations was moldy and black w ith a thin film o f whitish mold and w ith little remaining strength. Moisture contents o f 20 - 30% resulted in musty-smelling, deteriorated straw. This information tells us th a t a t moisture contents below 12% by w eight, the straw is likely to be structurally sound and unaffected by moisture. On the other hand, moisture contents o f 20 percent to 25 percent and more seems to result in mold, rot, deterioration and other moisture problems. The investigations also showed th a t a single incident o f high moisture content, followed by rapid drying does not seem to result in permanent moisture problems, providing that thorough drying is permitted before dosing in w ith stucco." 85 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.2.2 Portland Community College - straw Bate Construction Research Project This m oisture documentation was recorded from tests conducted on the Portland Community College (PCC), which was constructed by students and sta ff in August 1995 to serve as a test structure to determine the viability o f straw bale construction in rainy clim ate. Some o f the more noteworthy points o f this project are: • The clim ate o f northwestern US w ith its long rainy winters would seem to be the worst fo r straw bale construction. Yet the test results show a reduction in the moisture content o f the bale walls over the tim e. • The entire outside o f the building is wrapped in Tyvek and polyethylene was used as a vapor barrier on the inside. In spite o f these barriers the moisture content remained well below dangerous levels. • The building is unheated and has no internal moisture generation. Some professionals believe th a t unheated strawbale structures are more prone to having moisture problems because there is no heat generated, which would help in the evaporation o f moisture. Others believe that the temperature differential is itse lf responsible fo r the condensation th a t occurs and therefore, raising the interior temperature by using heating devices would ju s t lead to greater condensation. A heater and hum idifier have been installed in the te st building to simulate an occupied residence and m onitoring is continuing. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 50 Construction Details for the Portland Community College The diagram above shows the moisture protection fo r the walls allowing them to breathe while keeping them protected from direct exposure to moisture. The foundation extends 8" above finished grade, w ith 15# fe lt paper and rigid insulation below the bales. The bottom row o f bales is wrapped w ith fe lt paper as a splash barrier, and the entire outside o f the building is covered w ith Tyvek, which is an air barrier. Polyethylene is used as a vapor barrier on the inside o f the structure. The building has tw o-foot overhangs on all sides and three layers o f cement-based stucco on the exterior. In addition to this perforated drainpipes were placed around the perim eter o f the building in the gravel bed under the foundation to remove unwanted subsurface moisture. Results: On both walls, the changes in moisture content correlates w ith rainfall; steadily increasing in the w et w inter months and decreasing in late spring and summer. The highest moisture levels are found a t the exterior base o f the north w all. This could be because o f rain hitting the base o f the wall or moisture wicking up through the bales o r both. 87 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In either case the moisture has to travel through the stucco, the a ir barrier, and two layers o f 15# fe lt paper, all o f which are relatively permeable. During the firs t year the moisture content in the north wall remained dangerously high through the warm summer. It dropped lower in the second year (summer 1997) and dropped even lower in the summer 1998. Moisture-related problems are most likely to occur where excessive m oisture remained in the wall during the warm summer months. The South wall, on the other hand, is dearly affected by the warm sunshine falling on it and is never in danger o f excessive moisture levels. c- o 8 c c - o 8 25 20 15 10 5 25 20 j 15 10! 5 80 60 40 N O R TH W UL-Cw tor W « ZTa - ..III.II . t l l l l l l . l . . . 1 1 1 “ SOUTH WALL-Cantor £ j i p W -'" _ ^ i l l t l . l n , . • J i i l i u i . J l l . r 1 0 M A NR TBCBMI UC (0 P ) , / \ \ / Ivi \ X , I T 1 ™ 1 7 1 1 1! i i 1 c- O 8 c- o 8 25 20 1 5 10 N O R T H W A L L 3— N T a — a - 2 t i S B -* 20 - 1 0 0 25 20 15 10 5 80 80 SOUTH WALL ! 1 - S ~ if s . — J -...III.II .llllln . .i..ii. J .In Mm-mi “ S / . s * X v s r a r a w T u c \ \ / i°n \ V . , 1 T 1 i i i ■ 11 1 1 T I 1 0 0 7/2/96 7/1/96 7/1 /9 7 7/1/98 7/1/90 7/2/96 7/1/9B 7/1 /9 7 7/1/98 7/1/90 Fig. 51 Above Left: Moisture Content a t the Exterior o f the Wall Above Right: Moisture Content a t the Center o f the Wall 88 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Over the three years, the m oisture level appears to be dropping. This could be explained due to building materials such as the stucco itse lf contributing to the high moisture loads in the firs t year. The bales used fo r the testing had measured moisture content o f less than 13% and so it is safe to assume that the bales were not the moisture source. The decreasing trend is not attributable to the rain because in the firs t tw o years rainfall actually increased and was greater than normal by about 30% and 50% respectively. 25 20 15 10 5 nrvwminN 8 £ ■ V - 7 " W \ - - i i 1 I 1 t 1 1 1 L 1 L. ..L.L L .L .i , t i i 2 rW M IM 0 t r-~ MAMA / y / mrawuui \ \ / E < 0 F ) V r \ 1 T 1 i i \ i i n 1 1 1 TASS 7/1/B 6 7/1/87 771/88 7/V9B Fig. 52 Comparison o f the Moisture Contents fo r the North and South Walls Moisture measurements fo r the centers o f the wall follow those fo r the exterior w all, but they lag by a few months and are more attenuated. This would be expected since moisture moves from the exterior to the center o f the wall. 89 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In the late spring and summer w ith ambient temperatures increasing and minimum rainfall, the movement o f moisture reverses and the wall begins to dry out long before any substantial moisture has penetrated to the center o f the wall. The test shows th a t (1) an unoccupied but w ell constructed building appears to be a viable proposition in the Pacific Northwest and (2) w et construction materials such as stucco seem to add a significant moisture load in the firs t few years, which then decreases over tim e. However, these results are fo r an unoccupied building in which there is no internal moisture generation and so the results could be misleading and should not be applied to heated buildings w ith moisture generation." 7.3 Seismic There is little seismic te st data available fo r strawbales. In response to this lack o f data, the California Straw Building Association (CASBA) is developing a Strawbale Seismic Testing Program. The tests aim to collect data on cydic-load versus deformation curves fo r various bale walls. A cyclic te st w ill allow engineers to get information on in itia l strength and stiffness and to quantify the seismic-energy-absorbing capabilities o f a wall in terms o f strength, stiffness and toughness. In particular, importance w ill be given to the mode o f failure and type o f damage. The firs t phase aims to test a series o f extemal-mesh-reinforced walls. The design is based on the idea o f developing a ductile straw core enclosed inside a structural mesh cage. The trapped straw core w ill behave like a diagonal stru t under compression when the w all deforms and w ill carry loads long after the plaster skins are damaged. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The test frame w ill consist o f the long-stroke hydraulic rams mounted on opposite sides in a steel reaction fram e. This frame w ill be mounted on a concrete base to simulate a concrete footing w ith various connections. The rams w ill be pushed in opposing directions, generating a cyclic load. The gauges on the ram w ill be calibrated to measure the force o f the push and the deflection o f the w a lls/ Fig. 53 The Test Frame 7 .4 S tructural 7.4.1 Ghailene Bou-Ali Tests Structural tests were carried out on strawbales as a result o f the collaboration o f an advisory group o f building professionals, code officials and Out On Bale, Ltd. The tests were part o f a Masters Thesis fo r Ghailene Bou*Ali, a graduate student in Civil Engineering a t the University o f Arizona. Ghailene's firs t tests consisted o f compressive testing o f individual bales. Next, 9 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. nine w all panels 12 feet long by 8 feet high and 23 inches thick were b uilt so th a t three repetitions o f different sets o f tests could be carried o u t These were compressive strength, lateral-in-plane loading (force applied to the end o f the w all) and lateral-out-of-plane loading (force applied to the face o f the wall much like a wing force). The three tested walls were loaded w ith 16,000 pounds each. The vertical compression was measured and recorded. The bales were not plastered and three-string wheat bales were used. The panels tested fo r in-plane lateral loading received loads o f about 2,000 pounds. The horizontal deflection a t the top o f the wall was measured fo r each o f the three w all panels. The three walls were also tested fo r out-of-plane loading equivalent to about a 100-mile an hour wind blowing against the wall. In-P lant Lateral Out-of- Out-of-Plane Lateral Fig. 54 The Loading Diagram 92 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.4.1.2 Compressive Test Results The compressive testing o f the bales showed great resistance to failure when laid fla t. The average loading per bale a t failure was over 72,600 pounds, the equivalent o f 10,000 pounds per square foot. At this load, the testing machine sensed a change in the resistance o f the bales but none o f the ties broke. The average deflection o f the bales a t the failure load was about half o f the original bale height. However, the bales were found to be greatly elastic and returned to almost th e ir original height after removal o f the load. This characteristic is known as elastic deformation and is a desirable property because it suggests th a t the bales have the capacity to handle large short-term loads w ithout permanently losing their shape. The bales laid on edge showed significantly lower load bearing capacity and failed a t an average o f 13,850 pounds, which is only 2,770 lbs. per square foot. The mode o f failure was also more explosive w ith the ties breaking. The results from the wall panel tests were also impressive. The panels were loaded with 15,800 pounds on each o f the three panels, which showed an average deflection o f 7 inches under fu ll loading. This is equivalent to an extrem ely heavy roof load over a very large area. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.4.1.3 In-plane Lateral Loading The panels tested fo r in-plane loading showed an average deflection o f about 4" a t the top o f the w all, when 2,135 pounds was applied to the wall end. I t should be noted th a t there was considerable difference in the deflection exhibited by the three panels. This was apparently related to the degree o f tightness o f the nuts fastening the roof plates down. The tighter the nuts, the smaller the noted deflection. One o f the panels had the nuts tightened, as it would be on a normal wall system a fte r settlem ent o f the walls under fu ll roof load, and then they were re-tightened. This panel reflected a deflection o f 2-3/8" and more accurately represents the performance o f a fu lly loaded strawbale wall in an existing structure. DouM* 2" X4a Roof Plate 2" X 6" Croaa M e w ibei - Flake Half Bale — S’ Lonf #4 Ref ear PIn* < V2* Threaded Couplng Nut > #4 R ef e ar Pi n > 1/2" Anchor Bolt - Concrete Slafe^ \ 1/2* Nut A Waeher J_ “ I T T n / 1 J 1 1 _ J i 1 J pr s I I I r, i M i i i t ' asBS9 G6 BBg 6 Be ? * e s e s a s L 7 € e e 6 B 6 e L w & B f & a z s B B B a f i j f B e s f i 1 2 * Fig. 55 A 12 fo o t by 8 foot wall te st panel 7.4.1.4 Out-of-plane Lateral Loading The panels tested fo r out-of-plane lateral loading also performed very well. At the middle o f the panels, the horizontal deflections o f the three panels averaged less than one inch. This is very positive, especially since adding plaster to the wall panels would add considerably to the strength o f the w alls.* 94 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.5 Thermal There have been several therm al tests performed on strawbales w ith widely varying results. Original tests on strawbales revealed very high R-values fo r the bales, while later tests have produced results that daim lower R-values for the bales. The type o f bale, its density and its moisture content greatly affect test results. 7.5.1 McCabe Tests Much o f the earlier test results on strawbales were published based on measurements done by Joseph McCabe a t the University o f Arizona as a part o f his Master’s thesis. Testing followed the guidelines set by the American Society fo r Testing and Materials (ASTM) and used a Guarded Hot Plate apparatus. Insulating materials being tested surrounded the hot plate and the temperature o f the radiant heat panel was regulated using a DC power supply. Heat flux sensors were used to record temperature measurements. The main goal o f the tests was to obtain constant tem perature readings through out a sample test area o f the bale. The test showed an R-value o f 48.8 fo r a bale laid on edge (16.5" w idth) and 54.8 for a bale laid fla t (23" w idth). Thus the conclusion stated th a t the insulating value was R-2.68 fo r a bale laid on edge (where the heat flow is perpendicular to the orientation o f the straws) and R-2.38 per inch fo r a bale laid fla t edge (where the heat flow is parallel to the orientation o f the straws). 7.5.2 Othgr Test? Follow-up tests conducted have given widely varying results. In 1994, the Sandia National Laboratory used a thermal probe to deduce the R-value o f a 16 1/2" wide bale as R-44, which seemed to support McCabe's findings, but the test method used was quite prim itive. 95 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In 1996 the Oakridge National Laboratory (ORNL) constructed a bale w all th a t was plastered w ith stucco on the cold side and covered with gypsum drywall on the warm side. The tests found the R-value to be only R-17, which is R-0.94 per inch, which was very low compared to the previous test results. Several researchers suggested th a t the reason fo r the low R- value was the connection between the drywall and the strawbales, which could have set up convection currents in the w all, which depressed the R-value. In 1997 the California Energy Commission (CEC) conducted th e ir own tests. Two straw bale walls were built, both plastered on both sides, one w ith the bales laid fla t producing a 23" thick w all and the other w ith bales laid on edge producing a 16" thick w all. The walls were then tested in the company's new state-of-the-art guarded-hot-box apparatus. W ith the bales laid fla t, the R-value was R-26 and with the bales on edge the R-value was R-33. However, on disassembly o f the walls, the walls were found to be quite wet. W ater had been sprayed onto the stucco to prevent it from cracking and the walls had been tested only a week after this had been done. Also the bales had were not adequately compressed resulting in a 3" gap a t the top filled only with loose straw. Upon disassembly it was found th a t there were voids in the walls on the top. Finally the ORNL conducted a second set o f tests in th e ir guarded-hot-box apparatus. Bales were 19" wide and stacked fla t A fter being plastered on both sides, the wall was allowed to dry fo r almost tw o months. The temperatures inside the test chamber was kept a t 70F and outside a t O F and tw o weeks were provided fo r the walls to reach steady state heat flow conditions. The R-value was found to be R-27.5, this is R-1.45 per inch. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. This test value is accepted to be the m ost accurate measurement fo r the R-value o f bales to date. It is considerably lower than the values suggested by Joseph McCabe's tests and shows the influence o f proper installation and moisture penetration on te st results. Test procedure H otplate, single bale Thermal probe, sinqle bale Hot box, fu ll wall Approved values Hot box, fu ll wall Hot box, fu ll wall Test date 1993 1994 Oct. 1996 Dec. 1996 May 1997 Feb. 1998 Type o f straw Wheat Not listed Wheat Any Rice Wheat Type o f bale 3-string, 23 inch 2-string, 18inch 2-string, 18 inch 3-string, 23 inch 3-string, 23 inch 2- string, 19 inch Moisture content 8.4% Not listed Not listed 20% 11% 13% Density Ib/ft3 8.3 5.2 Not listed 7 6.7 8.0 R-value/in 2.38 2.67 .94 .56-.91 1.13 1.45 R-value 55 48 17 13-21 26 27.5 Table 9” Straw bale R-values ' Ed it e d b v Kell y Lemer and P a m e la W ad sw cxt h Goode . The B ui ld in g Offi ci al ’s Guide to Sf r aw- bat e Cons t r uct i on. V er si o n 2.1 ( publi shed b y The St r aw B u ild in g As so ci at io n © 2000) pp. 78 * E d it e d bv Ke lly Lemer a nd P am e la Wa d s w o rt h Goo de . The B u ild in g Offi ci al' s Gui de to St raw- bai e Cons t r uc t i on. V er si o n 2.1 ( publ i shed by The St r aw B u ild in g As so ci at io n © 2000) pp. 80 m E d ite d bv Kdi v Lemer a n d Pa m el a Wa d s w o r t h Good e . The Bu ilding Offi ci al ' s Guide to St raw- bai e Cons t r uct ion. Ver si on 2.1 ( publ i shed by the Cali f or nia St r aw Bu ilding Ass ocia tion © 2000) pp. 67-09 * E d it e d b y Ke lly Lemer a n d P am ela Wa d s w o r t h Go o d e , The B u ildin g Offi ci al ' s Gu id e to St r a w- t > a le Const r uct i on. Ver si on 2.1 ( publ i shed by the Cali f or nia St r aw Bu ilding Ass ocia tion © 2000) pp. 69-70 v The La st Shaw. I ssue #25, Sp ring 1999 ( publi shed b y Net wor ks P r odu ct ions , In c) pp. 24-25 * The La s t Straw. I ssue #4, Sum me r 1993 ( publi shed by Net wor ks Pr oduc t ion s, In c) pp. 11-13 v ii S o u rc e: Co m m in s an d St one , Tested R- value for straw B a le Wall s a nd Per f o r manc e M o d e ling for Straw B a le Ho m es ", 1998 ACES S u m m e r S t u d y on E n e r g y Ef f ici e nc y i n Bu ild in g s P r o c e e d in g s 97 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8. THERMAL TESTS ON STRAW BALES 8.A Hypothesis The research in this report is used to support the follow ing hypothesis: The i n su l a t i on val ue o f st raw bal es changes w i t h t h e o ri e n t a t i o n i n whi ch t hey a re pl aced i n a bal e w a l l assem bl y; th a t i s to say th a t t h e R - val ue o f a st raw bal e l a i d fla t d i ffe rs f ro m t h e R- val ue o f a bal e l a i d on edge 8 .2 Relevance o f Tests To date, there have been several thermal tests carried out on strawbales by various organizations and individuals w ith varying results. There is always the need to reduce or minimize construction costs, w ithout compromising the performance o f the m aterial. The tests on the bales should provide an indication o f the R-value (the resistance to heat flow ) o f the bales when laid fla t (w all thickness 23") and when laid on edge (w all thickness 15 1/2"). I f these values turn out to be almost sim ilar, then the builder has the option o f using bales on edge, thereby reducing cost while maintaining the t herm al performance o f the wall system. I f the R-value is proportional to the thickness o f the bale, then the bales laid on edge w ill have a lower R-value than those laid fla t. However, if cost rather than thermal performance is a primary consideration then depending on the type o f construction, the owner has the option o f using bales laid fla t or laid on edge. 8 .3 Method O f Testing S tatistics 1. Wheat strawbale 2. Three-string bale (dimensions 45" x 23" x 15 1/2") The bale was tested by enclosing it in a well-insulated box. The box comprised o f several layers o f polystyrene insulation on three sides and the top and bottom o f the bale. 98 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The polystyrene has an approximate R-value o f 4.5 fo r 1-1/2" thickness (the exact R-value o f the polystyrene insulation is not critical to the experiment but has been documented anyway). The firs t part o f the experiment used the bale laid on edge (height = 23" and width = 15 1/2"). The bale was placed on top o f and covered w ith nine inches o f polystyrene insulation. Nine inches o f insulation was also placed along both its short sides and along one longer side keeping a distance o f about 23" between the bale and the inner most layer o f insulation. On the other long side a two-inch thick DOW blue board (styrofoam ) w ith a known R-value o f five (ft2 °F/ Btuh in) was placed against the long face o f the bale. The heat source was provided by a 7W incandescent light bulb. Care was taken to seal a ll joints w ith silicone latex sealant and duct tape. The insulated box was constructed firs t leaving the top nine inches o f insulation unattached to allow fo r turning the bale in the second phase and fo r inserting the lig h t source. The bale was then placed through the front open end o f the box and the DOW blue board placed against the bale. Temperature sensors (8K StowAway tem perature loggers w ith internal and optional external sensors - model no. XTT08 -39 °C to 122 °C) were then placed along the inner face o f the bale, a t the interface between the bale and the DOW blue board and on the exterior o f the blue board. For the test runs two sensors were used on the inside o f the cell and the outside, w ith no sensors between the bale and the styrofoam. The final readings were recorded o ff three sensors placed a t all three locations. The sensors were pre-programmed to record temperatures at 15-minute intervals using software called Logbook2. They were linked via a cable to the computer and the information downloaded into graph and te xt form at using the same software. To prevent any single sensor being exposed to direct radiation from the heat source, a w hite reflective surface was placed in fro n t o f the heat source to enable accurate temperature readings o f ambient a ir temperature inside the box. To prevent escape o f heat from around the edges o f the bales, an extra six inches o f insulation were placed against 99 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. both vertical edges on the inside face o f the bale. During the entire process, the bale was kept stored in a clean, dry indoor space to prevent any possibility o f m oisture seepage into the bale. All the sensors were normalized before final readings were taken to ensure maximum accuracy. The R-value o f the bale was then calculated based on the tem perature gradient between various surfaces i.e. the inner warm side o f the bale, the cold side o f the bale and the outside face of the styrofoam. Since the R-value o f the styrofoam is known (R-10), a comparative value fo r the bale could then be calculated. Fig. 56 Phantom drawing o f general experiment set-up showing positions o f temperature sensors 100 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 KtrUCTivt SMffel ' , to ntitAT e*fct '^ k i's s s r Fig. 57 Location o f Temperature Sensors on the Outside o f the Test Cell (prior to sealing) when the bale is laid on edge 2 * Milt B O M S S T V C O f O A M S T p M f i A U ■ r K T«TT |«M t IMSuUfWM TCNTCIUTMC s c to o ts U F ic c T iy t s u tm c t T o ruvtMT M f t C t UMttSi WAT LOSS Fig. 58 Location o f Temperature Sensors inside the Test Cell when the bale is laid on edge 101 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8.3.1 The Heat Source To estimate the wattage o f lamp to be used inside the box, a conservative calculation was used. The assumption made was th a t all the light produced by the lamp is converted to heat, which passes ONLY through the width o f the bale. We assumed th a t there was no heat loss through any other surface inside the box. qc = U x A x AT Where U = 1/SR (assumed as an average value o f 40 fo r the bale and known value o f 10 fo r the DOW styrofoam board) A = (23 x 16)/144 = 2.5 sqft (area o f the bale surface through which all the heat is assumed to flow ) AT = 20 F which is the desired temperature differential between the inside and outside o f the box. = 3 .4 W where W = lamp wattage Therefore: qc-<fc U x A x AT = 3.4 W So... W = (U x A x aT)/3.4 {1/(40 + 10) x 2.5 x 20} / 3.4 = .29W This gives a conservative value fo r the lamp wattage, which would achieve a twenty-degree temperature differential and avoids any danger o f overheating during long, unobserved periods o f data collection. 102 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9,3.2 Nomenclature The results from the tests were plotted as graphs in Excel using the follow ing nomenclature: Ti - Temperature inside the test cell Tx - Temperature between the bale and the styrofoam T0 - Temperature outside the test cell ATS - Difference in tem perature between the inside o f the te st cell and the sensor placed between the bale and the styrofoam ATd - Difference in tem perature between the outside o f the te st cell and the sensor placed between the bale and the styrofoam ATs/ATd - Ratio o f tem perature differential caused by the strawbale to th a t caused by the styrofoam S T f U W & A L E a ? e u > e b o a a p s t y iu > p o » m XEFlecTwt s m q A & E - o > p re v e n t noser h a c m tk m heA T S O U R C E I NSU L AT I ON T o m .V tN T HEAT LC S S F R O M EOS IS ST fb L Y JT Y R E K t IN S U LA TIO N Fig. 59 Section o f test cell w ith bale laid fla t (th k = 23") 103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. S fp A M B A L C a . " e u > e taAft* «rrpfa*M .jtm e e tw t sixM ct 1 0 RMMT P i p E C J pPIATMrt M A T SOUftCt IMSVLATVM T 9 P ttV tM T HEAT L a m f W M B ale, coses S S S t^ B P * ' Fig. 60 Section o f test cell w ith bale laid on edge (th k = 15 1/2") 8.3.3 Test Sequence 8.3.3.1 Test 1 - w ith 3W Lamp To be cautious, the lowest available lamp wattage was used. A 3W incandescent lamp was placed inside the insulated box fo r a period o f tw enty-four hours. The temperatures from the sensors was downloaded and computed into graphs using Log boo k2 and M S Excel. From Fig. 61, the interior temperature graph (T i) seems to follow the outside temperature (To), showing a corresponding rise in temperature inside when there is a rise in the outside temperature (a t around 1:00 p.m .). The same is true when there is a drop in the temperature outside. The diurnal fluctuation fo r the outside temperature is about 7 degrees (varying from about 75 F in the afternoon to about 69 F in the morning), whereas inside the insulated box, the tem perature fluctuation is much less, only about 11/2 degrees (varying from about 71.5 F to 73 F). This suggests th a t the strawbale is successfully moderating internal temperature but there is some air leakage through the box resulting in a drop in 104 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. temperature inside. There is also a negligible tem perature differential suggesting th a t a higher wattage lamp may be required. N ot e: The experi m ent was conduct ed i n a woodshop fo r archi t ect ure st udent s w her e t h e t em perat ur e i s regul at ed b y a t herm ost at . Dat a fo r Taat 1 - wri tl i 3W Lamp Fig. 61 Inside (T i) and outside (To) tem perature graphs fo r Test 1 8 .3.3.2T est2 -w ith 5W Lamp The second test was conducted using a 5W lamp as a heat source. The test cell remained in the woodshop, but a 5W lamp replaced the 3W lamp. The inside temperature graph shows a steady increase in temperatures from about 71 F to 77 F in about six hours. The temperature appears to have stabilized a t about 77 F. The temperature in the woodshop, however, shows an expected temperature fluctuation w ith the lowest temperature o f about 65 F occurring early in the morning and a peak tem perature o f about 69F occurring in the late afternoon (possibly due to students using the various machines). The graphs indicate th a t the strawbale acts as an efficient insulating m aterial, effectively isolating temperatures 105 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. inside the test ceil from fluctuations outside in the woodshop. Since the temperature inside the ceil seems to rise steadily, the insulated box appears to be w ell sealed w ith little air infiltration from the outside. However, the temperature differential is s till only about 9 F. Therefore, it is possible to use a larger lamp o r to try and leave the 5W lamp inside the cell fo r a longer period o f tim e. Data ta r T « t 2 - w toi 5W Lamp 3 a 8 S 8 S 8 S 8 S 8 S 8 S 8 S 8 S 8 S 8 S a a s a s a a a s a s s s s a a s * - - o * 8 8 8 Fig. 62 Inside (T i) and outside (To) temperature graphs fo r Test 2 8.3.3.3 Test 3 - Second run w ith 5W Lamp The test cell, fo r this third experiment was moved from the woodshop to a high-ceiling, large space where the cell was placed near a West wall w ith a window. The 5W lamp was placed inside the cell, which was thoroughly sealed fo r a period o f three days. The temperature readings were recorded a t the end o f the test period. The graphs seem to indicate th a t the leakage is greatly reduced because the interior tem perature continues to rise even though the outside temperature keeps fluctuating. 106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. There is a steady rise in the tem perature from about 61 F to about 68 F in a period o f three days. The tem perature outside the cell however fluctuates w ith a low o f 52 F to a high o f 62 F. This is a large temperature fluctuation and might be caused fo r two reasons: 1. The temperature peak which occurs a t about 4:00 p.m. m ight be due to the sun's rays coming in through the windows in the building and directly striking the sensors, causing the tem perature to peak a t th a t tim e. 2. The fluctuation may also result from other activity such as people entering and leaving the space and opening o f the door. The tem perature pattern inside the cell once again indicates th at the strawbale is an effective insulation material. However, because o f the irregular fluctuation in the space outside the te st cell, the temperature differential is not steady and fluctuates. Moreover, the 5W lamp provides an insufficient temperature differential, suggesting th a t a higher wattage lamp should be used. /Mote; Thi s phase o f t he experi m ent was conduct ed i n a h i g h -ce i l i n g st orage space, wher e t he t em perat ure i s n o t regul at ed. O t her peopl e al so have access to th i s space, re su l ti n g i n g re a te r t em perat ure f l u ct u a t i o n s i n si d e t h e space. M h f M l ' i n r i m a l l i n r i i a p Fig. 63 Inside (T i) and outside (To) temperature graphs fo r Test 3 107 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ^ 58 ^ 8 ^ 82 ^ 2 ^ 8 ^ 8 ! 2 ^ 8 ^ 8 S ^ 8 S ^ 2 ^ ^ 8 ^ 8 » ^ ! 2 ^ ! a ^ ! 2 S«!8 ! 2 Si «82 S W ! Fig. 64 Temperature differential between inside and outside o f test cell 8.3.3.4 Test 4 - w ith 7W Lamp The test cell was kept in the same space but the 5W lamp was replaced w ith a 7W lamp. The cell was well sealed and readings taken fo r a period o f two and one-half days. This tim e, sensors were placed in between the bale and the styrofoam as w ell. The temperature outside the test cell (T0 ) shows a ten-degree daily fluctuation from about 57 F to about 67 F. There are peaks at about 4:00 in the afternoon as in the previous test, indicating th a t this is indeed a result o f the sun's rays striking the sensors. From a comparison o f the sensors inside the cell (Tj) and a t the intermediate position (Tx ), we can see th a t the graphs appear to have almost identical temperature patterns. The temperature inside the test cell appears to be rising steadily from about 63 F to 73 F. The sensors in the middle also show a steady tem perature rise from about 60 F to 66 F. The strawbale appears to exhibit no tim e lag a t all w ith both graphs showing a steadily rising temperature. Fig. 67 shows the ratio o f the insulation provided by the straw bale to th a t provided by the styrofoam (Ts/Td). 108 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The graph is asymptotic in nature w ith the curve tending to flatten out followed by a sharp rise in the temperature a fte r which the curve flattens again. Therefore, the average ratio would be the average o f the lowest values in the graph where the curve is asymptotic in nature. The lowest value o f the asym ptotic curves occurs between 4:30 am and 8:00 am on the 7th o f March (ratio is 1.30 a t this tim e) and between 3:15 am to 4:00 am and 5:15 am to 7:15 am on the 8t h o f March (ra tio is 0.98 a t this tim e). The average ratio would therefore be (1.3 + 0.98)/2 which is about 1.14. Since the R-value o f the styrofoam is already established as R-10, it follows th a t the comparative resistance value fo r the bale would be R-11.4. Because o f the asymptotic nature o f the curve the average value cannot be the average o f all the values, but is the lowest value a t the point where the asymptotic curve is constant. Dat a to r T « t4 -w M i7 W L a mp SS8¥S;28SS28SS28!fS28¥S28»S28SaSSS8¥SS8!SS28¥S28¥S:28¥S!28SS!28¥SS8¥*2 a S T I Fig. 65 Inside (T( ), middle (Tx ) and outside (T0 ) temperature graphs fo r Test 4 109 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. T n wrat o f d *» f c r T t 4 -w t« l 7W U H w p Fig. 66 AT, and ATd - Temperature differentials fo r Test 4 T fc m p v B tM dNVwtM ftttoofibMMitotfyvofDMii Fig. 67 Ratio o f tem perature differential from strawbale to styrofoam fo r Test 4 110 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8.3.3.5 Test 5 - Second run w ith 7W Lamp For this test the 7W lamp was le ft inside the test cell fo r a period o f ten days. Three sensors were placed inside the te st cell, three more in between the styrofoam and the bale and three outside the test cell. The test was conducted during Spring break so the woodshop was dosed fo r a week during the test. This means there were no students entering or leaving and the temperature remained fairly steady. The temperature inside the test cell (T ) and the temperature between the cell and the styrofoam (Tx ) peak and fa ll a t the same tim e showing th a t strawbale has no thermal storage capacity. There is a two-degree temperature fluctuation in the temperature inside the test cell. Fig. 68 Inside (T ), middle (Tx ) and outside(T0 ) temperature graphs fo r Test 5 111 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Tamparat ura dffl arantial data fc r Taat S • wNh TH l am p Fig. 69 ATS and ATd - Temperature differentials fo r Test 5 Fig. 70 Ratio o f temperature differential from strawbale to styrofoam fo r Test 5 112 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 69 shows the comparison in the temperature differential between the inside o f the test cell and the middle layer (Ts ), which is caused by the strawbale and the middle layer and outside o f the test cell (Td ), which is caused by the styrofoam. I t indicates th a t the strawbale is providing about the same amount o f insulation as the styrofoam and so the R- value o f the bale is probably dose to that o f the styrofoam. Fig. 70 shows the ratio o f the tem perature differential provided by the bale to th a t provided by the styrofoam, once again the graph is a series o f asym ptotic curves tending to zero and so the average ratio would be an average o f the lowest values o f the curves. The graph shows an emerging pattern w ith a high peak occurring around 4:00 pm in the evenings almost everyday after which the curve assumes the shape o f an asymptote again. Therefore, we can assume that if the anomalous peak did not disturb the tem perature pattern, then the lowest point o f the asymptotic curves would be the point a t which the temperature would begin to stabilize. The lowest temperatures occur a t the tim es given below : 10t h March - 8:15 am -1 .0 8 l l m March - 5:45 - 6:00 am -1 .0 9 12t h March - 5:15 - 6:30 am - 1.08 13“’ March - 7:15 - 8:00 am - 0.57 14t h March - 8:30 -11:00 am - 0.69 15t h March - 4:45 - 5:30 am - 0.63 16t h March - 7:15 - 8:30 am - 0.63 IT * March - 6:15 - 6:30 am - 0.58 18t h March - 5:00 am - 0.58 19t h March - 9:15 am - 0.63 The average o f these values is 0.756 113 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Since the R-value o f the styrofoam is known as R-10, this would give us an R-value for the bale o f R-7.5. This is a very low value fo r the insulation o f the strawbale. Since the bale used was very dry and carefully stored and since the problem o f a ir leakage from the sides o f the bale was largely eliminated, it follows th a t there may be some other problem in the experim ent There could be convection currents set up w i th i n the bale and perhaps even through it to the interior o f the test cell, which are responsible fo r the drastically low R-value. So, the next stage w ill involve wrapping the bale in cellophane, which has a negligible R-value but w ill effectively cut o ff any convection currents. 8.3.3.6 Test 6 - w ith 15W lamp The 7W lamp was replaced by a 15W lamp, which was placed in the test cell for a period o f five days. The straw bale was wrapped in cellophane to ensure th a t any convection currents (which m ight be responsible fo r a lowering the R-value) through the bales would be cut o ff completely from the inside o f the te st cell. The cellophane has negligible R-value and so w ill not affect the readings fo r the R-value o f the strawbales. The te st cell was sealed and readings recorded over a period o f five days. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Data for Taat ■ - wtth 15W Lamp Fig. 71 Inside (Tj), middle (Tx ) and outside(T0 ) tem perature graphs fo r Test 6 Tanpm tura K V m M W i for T m t • - wMi 15W l a m * ra 5 T Fig. 72 ATS and ATd - Temperature differentials fo r Test 6 115 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 73 Ratio of temperature differential from strawbale to styrofoam for Test 6 Fig. 71 shows a comparison between Ti, Tx and T„ a t a ll three positions in the test cell. Fig. 72 is a comparative graph showing the tem perature differentials across the different layers. Fig. 73 shows the ratio o f tem perature differential provided by the bale and styrofoam . The graph is mostly constant w ith small peaks occurring in the afternoons. Once again the average ratio is calculated as the average o f the lowest values o f the asym ptotic curves. These occur a t the times given below: 22n d March - 6:30 - 7:15 am - 1.42 24th March - 5:30 - 6:15 am -1 .1 5 25t h March - 7:00 am -1 .2 6 26“’ March - 6:45 - 7:45 am -1 .2 6 The average o f these values is 1.27, which would give a comparative R-value o f R-12.7 for the strawbale. The outside temperature graph (T0 ) in Fig. 71 shows a temperature fluctuation from 67 F to about 73 F, which is about six degrees. This fluctuation is s till too large and maybe a possible reason fo r an inaccurate R-value. 116 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8.3.3.7 Test 7 - w ith 25W lamp The 15W lamp was replaced by a 25W lamp and the te st cell placed in an air-conditioned room. Temperature readouts were taken fo r a period o f two and one half days. Unfortunately, the refrigeration system was switched o ff during the night and turned on during the day resulting in a higher temperature during the night and a lower temperature during the day. So, there was s till a noticeable fluctuation in the outside temperature. Fig. 74 Inside (T|), middle (T„) and outside(T0 ) tem perature graphs fo r Test 7 Fig. 75 ATS and ATd - Temperature differentials fo r Test 7 117 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. MIIIIMIMMMlflWWjAMIIIMMMMIIIjlllAMMIItMtflWMIHIWlAtftMMMMMMWItAMIMMlllMMtflMMMMMMIAlAMIVtMIMMMWMHtMIIIIMMMM Fig. 76 Ratio o f temperature differential from strawbale to styrofoam fo r Test 7 Figure 75 shows the temperature differential between the different layers in the te st cell. Due to the outside temperature fluctuation (T0 ), the temperature differential also shows a fluctuation. Fig. 76 gives a ratio o f the differential provided by the bale to th at provided by the styrofoam. The lowest values o f the asymptotic curves occur at: 6 * * 1 April -10 :1 5 pm - 1.35 7 * April - 6:30 - 8:00 pm - 0.86 8t h April - 8:00 - 9:45 pm - 0.76 The average value is 0.99, which would give an R-value fo r the bale o f R-9.9. This is the same R-value as tha t o f the styrofoam. 118 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. N ot e: The l am p sour ce i n th i s experi m ent was f ound to have f a l l e n agai nst th e i n n e r m ost l a ye r o f pol yst yrene i nsul at i on a t t h e re a r o f t he te s t c e l l , m aki ng a sm al l hol e i n t h e l a tte r. D espi t e t h e t hi nness i n t h e re a r l a ye r, t h e R - val ue shoul d n o t be a f f e ct ed because we are s till com pari ng t h e gra di e n t o n l y across t h e l ayers th a t a re bei ng measur ed. 8.3.3.8 Test 8 - w ith 25W lamp (bale laid fla t) For this second test, the straw bale was turned fla t so th a t its width now measures 23 inches and the height, 16 inches. I t was wrapped in cellophane and an additional 7.5 inches o f insulation were placed above the bale to dose the gap between the top three layers o f insulation and the strawbale. A 25W lamp was used as a heat source and the heat flow was prim arily across 23 inches (bale w idth). Six inches o f insulation were placed overlapping the edges o f the bale to prevent heat loss from the edges. A w hite reflective surface was placed between the lamp and the sensors on the inside surface o f the straw bale, to elim inate direct radiation. The sensors were placed in the same positions as fo r the previous series o f tests; three on the inner hot surface, three between the bale and the styrofoam and three on the outer face o f the styrofoam. The cell was well sealed and readings recorded fo r a period o f three and one half days. A comparison between T„ the temperature inside the te st cell, and Tv the tem perature between layers, shows th a t although the temperature between the bale and styrofoam follows the internal temperature w ith simultaneous rises in temperature, the variation in Fig. 77 is much higher. This indicates th a t the bale is providing much greater insulation than the styrofoam is. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dat a fe r T a m ■ -a H O i 2 5W L a mp (bal al aM fla t) Fig. 77 Inside (T( ), middle (Tx ) and outside(T0 ) temperature graphs fo r Test 8 :a*8 =8 «82a*?i=aT8 £a«8 s a *s = a *3£ a * 9a8« 8a a * 8 =a<i82a * 8 aa«82a«!S£Si#?aa»aaaif8 = a *8aa#82S i Fig. 78 ATS and ATd - Temperature differentials fo r Test 8 120 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 82S!S8SSS82»!|!8Sa!S8SS!S8SS!P8aS!S8SS!!P828S88a*8KS!P8SSS8S8S8B»!P8S!«8SS*8K»!P § ^ T im Fig. 79 Ratio o f temperature differential from strawbale to styrofoam fo r Test 8 Fig. 79 gives the ratio o f the temperature differential provided by the bale to th a t provided by the styrofoam. The lowest values o f the curves are April l l m - 9:15 -1 0 :4 5 am - 7.69 April 12t h - 5:45 - 6:45 am - 5.33 April 13t h - 8:00 am - 4.66 April 14t h - 8:00 am -1 0:0 0 am - 4.70 The average value 5.59. Given the R-value o f the styrofoam as R-10, this would give an R- value fo r the bale, when laid fla t, o f R-56! 8.3.3.9 Test 9 - w ith 15W lamp (bale laid fla t) The experiment was repeated w ith a 15W lamp w ith the bale laid fla t. All the same precautions were repeated fo r this experiment. Fig.81 below shows a comparison o f the temperature differential provided by strawbale to th a t provided by the styrofoam. 121 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Again the temperature differential provided by the bale is much higher than th a t provided by the styrofoam indicating the bale has a much higher insulation capacity. The average ratio from Fig. 82 is calculated using the lowest values from the asymptotic curves. These are as given below: 3r d May - 12:30 -1 :0 0 am - 6.58 4t h May - 6:45 - 7:45 am - 5.01 5t h May - 5:15 - 5:45 am - 4.68 The average value is 5.35. Since the R-value o f the styrofoam is R-10, this would give an R- value fo r the bale o f R-53.5! This is consistent w ith the previous results obtained using the 25W Lamp. Dat a to r T art 9 - wMh 15W Lamp (>■<• M d fla t) 1 2 0 47.6 45.6 416 416 39.6 37.6 O 35.6 m 316 3L6 29.6 27.6 25.6 216 21.6 19.6 17.6 1 & 6 ■ Fig. 80 Inside (T i), middle (T ,) and outside (T0 ) temperature graphs fo r Test 9 122 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fig. 81 ATS and ATd - Temperature differentials fo r Test 9 I V n p V I I I R V O m W R M I w S w l Q I V M M CD KyTDVQDfn S S » 88B *8!2S y8 S S »8 !2 S **8B liW 8 8!5S *8!fiS *8 S »C 8 8*8K a *8S a *8 S »P 8 »8!S 8 *8S S » 8S » P 8S S » 8S Fig. 82 Ratio o f tem perature differential from strawbale to styrofoam fo r Test 9 8.3.3.10 Test 10 - with 7W lamp (bale laid fla t) The experim ent was conducted w ith a 7W lamp, which replaced the 15W lamp. The graph below shows the very sim ilar pattern between the inside temperature (Ti) and the outside 123 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. tem perature (To). Figure 85 shows the ratio o f temperature differential o f the strawbale to th a t o f the styrofoam. The graph shows a series o f asym ptotic curves interrupted by anomalous peaks. The average o f the lowest values o f these curves is used to calculate the average value o f the ratio, which is 3.5. This would give an R-value fo r the bale a t R-35. Fig. 83 Inside (T ), middle (Tx ) and outside (T„) tem perature graphs fo r Test 10 124 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. M W U M to r T K 10 - « HBl 7W I l » ( M i UK IM ) igy ytgy w yi w » b » ik > c « « S * ‘i Fig. 84 ATS and ATd - Temperature differentials fo r Test 10 Fig. 85 Ratio o f temperature differential from strawbale to styrofoam fo r Test 10 125 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8.3.3.10 Test 11 - Second run w ith 7W lamp (bale laid fla t) Another te st with a 7W lamp was conducted using exactly the same experimental setup. An attem pt was made to override the therm ostat settings in the woodshop. However, this is controlled by a central plant, which also controls therm ostats in other buildings on the campus and so the experiment was conducted w ith the therm ostat set to 75 F. Fig. 86 shows sim ilar temperature patterns as were noticed in the previous experiment in Fig. 83. Fig. 88 below shows the patterns o f the asymptotic curves, o f which the lowest values are used to calculate the ratio o f temperature differential provided by the strawbale to that provided by the styrofoam. The average value is 4.68, which would give an R-value o f R-47 for the strawbale. M u tar Ik * 11 - wM 7WUmp(Ma Htf ftat) Fig. 86 Inside (T ), middle (T„) and outside (T0 ) temperature graphs fo r Test 11 126 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 / 22/01 Tu y rH ura it W w illil d ^ a fa r T — t 11 - w ttti 7 W Lmi p ( ■■* ■ M d H t) Fig. 87 ATS and ATd - Temperature differentials fo r Test 11 T»/ Td - Tmnn rafti f i WN m i t ll pr ot r t dad by H m m bal i to t hat pr ovMad by it yr of oawi Fig. 88 Ratio o f temperature differential from strawbale to styrofoam fo r Test 11 127 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. gi-CQMCLU«OH This thesis has attempted to establish the R-value o f bales w ith the fibers oriented in different directions. The experiment was devised by Professor Schiler and myself with the resources th a t were available to us. I t is not an ASTM testing method but the experiment was conducted in natural conditions w ith external temperature variations. These are the conditions under which most straw bale buildings are b u ilt in reality. All the testing has revealed consistently different R-values fo r the bale laid in different positions. From the testing th a t has been done, the R-value o f straw bales laid on edge (w idth 15 1/2") ranges from R-7.5 to R-12.7, that is an R-value per inch o f R-0. 5 to R-0.82 per inch. All the testing has revealed consistently low R-values fo r the bale in this position. The second series o f tests were conducted w ith the bale laid fla t using the same lamps fo r the firs t set and under identical testing conditions. These tests w ith the bale laid fla t (w idth 23") reveal surprising statistics. The R-value in this position ranges from R-35 to R-56! which is an R-value per inch o f R-1.52 to R-2.43 per inch. This is very high indeed, especially compared to the low values when the bale was laid on edge. The 1997 California Energy Commission (CEC) tests revealed R-values fo r the bales laid on edge and laid fla t which are contrary to the results from the tests conducted in this thesis. In the CEC tests, the R-value o f the bale laid fla t (23" thk) was lower than the R-value o f the bale laid on edge (16" th k). These results are expected because when laid fla t the tubular fibers run parallel to the direction o f heat flow . One would therefore expect the heat to be carried rig h t through the fiber across the bale w idth, bypassing any thermal qualities o f the strawbale and greatly lowering the R-value. However, we see results th a t are contrary to this explanation. 128 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Test R -value (bale laid on edge • th k 1 5 1 /2 " ) R -value/inch (b a le laid on edge) R-value (bale laid fla t-th k 23") R -value/inch (b a le laid fla t) W ith 7W Lamp R-11.4 0.74 R-35 1.52 Second run w ith 7W Lamp R-7.5 0.5 R-47 2.04 W ith 15W lamp R-12.7 0.82 R-53.5 2.32 W ith 25W lamp R-9.9 0.64 R-56 2.43 Table 10 Table o f R-values using the temperature gradient method The tests seem to indicate that a bale laid fla t (w idth 23") has much greater thermal performance, th a t is to say that it is a much better insulator when laid in this position. It has already been established th a t in load-bearing structures, the code requires the use o f bales laid fla t fo r better stability. Therefore, a bale wall assembly w ith bales laid fla t (wall thickness 23”) would appear to be both structurally more stable and better in terms o f thermal performance. Bales laid on edge could be used when average therm al performance is required, but is not the primary design concern. In such a case, cost savings on bales and foundation costs would be dominating factors. It is not certain a t this tim e whether the discrepancy in R-values is due to fiber orientation or due to errors in the experiment. Although every e ffo rt has been made to eliminate all possible sources o f error, this is a student endeavor and there may have been unknown factors th a t resulted in such varied R-values. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The fluctuation in the external temperatures leads to a wide range o f R-values but not a singular value. The method o f calculation tries to minimize the impact o f external temperature variations by taking the average o f the lowest values, where the asymptotic curves flatten out. To confirm the findings in this series o f experiments, it is recommended th a t these tests be carried out in a controlled atmosphere, which would allow a steady state temperature to be reached. It is also necessary to find a way to test strawbales under natural conditions, which w ill give us an R-value fo r the m aterial in its most natural surroundings. For comparable results, it is also recommended th a t the processing methods and the growth conditions of the straw used fo r bales be documented during the tests. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10. BI BLI OGRAPHY 10.1.1 Books Elizabeth, Lynne; Cassandra Adams, Ed. Alternative Construction - Cont empor ar y Nat ur al Bu ild in g M e t h o d s . John Wiley & Sons, Inc., 2000. King, Bruce P.E. Buildings o f Earth and Straw - st ructural Deskm for Ra mme d Eart h a nd St r aw- bat e Ar chitect ur e. Ecological Design Press, 1996. Lemer, Kelly; Pamela Wadsworth Goode, Ed. The Building O fficial's Guide to Straw-bale Construction. Version 2.1, California Straw Building Association, 2000. Magwood, Chris; Peter Mack. Straw Bale Building - H o w to pl an, des ign & bui l d wi th straw. New Society Publishers, 2000. Myhrman, Matts; S.O. MacDonald. Build it w ith Bales - a steo-bv steo Gui de to straw-Baie const r uct i on. Version Two, Out on Bale Ltd., 1997. Steen, Athena Swentzell; Bill Steen; David Bainbridge. The Straw Bale House. Vermont: Chelsea Green Publishing Company, 1994. 10.1.2 Journals The Last Straw. Summer 1993, Out On Bale (un) Ltd. The Last Straw. Fall 1993, O ut On Bale (un) Ltd. The Last Straw. W interl993, Out On Bale (un) Ltd. The Last Straw. Spring 1994, Out On Bale (un) Ltd. The Last Straw. Summer 1994, Out On Bale (un) Ltd. The Last Straw. W inter 1994, Out On Bale (un) Ltd. The Last Straw. Summer 1995, Out On Bale (un) Ltd. The Last Straw. Fall 1995, Out On Bale (un) Ltd. The Last Straw. W inter 1997, Out On Bale (un) Ltd. The Last Straw. Spring 1999, Networks Productions, Inc. The Last Straw. W inter 2000, Networks Productions, Inc. 131 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10.1.3 Websites http://www.strawhomes.com Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11. APPENDIX1 11.1 C alifornia S tate H ealth and S afety Code 18944 11.1.1 18944.30 а) The Legislature finds and declares all o f the follow ing: 1) There is an urgent need fo r low-cost, energy-efficient housing in California. 2) The cost o f conventional lumber-framed housing has risen due to a shortage o f construction-grade lumber 3) Rice straw is an annually renewable source o f cellulose th a t can be used as an energy- efficient substitute fo r stud-framed wall construction. 4) The State has mandated th a t the burning o f rice straw be prohibited as specified in statute by the year 2000 in an annual phased reduction. 5) As a result o f the mandated burning reduction, growers are experimenting w ith alternative straw management practices. Various methods o f straw incorporation into the soil are the most widely used alternatives. The two most common methods are non- flood incorporation and w inter-flood incorporation. Economically viable off-farm uses for rice straw are not yet available. б) W inter flooding o f rice fields encourages the natural decomposition o f rice straw and provides valuable waterfowl habitat. According to the Central Valley Habitat Joint Venture component o f the North American W aterfowl Management Plan, in California's Central Valley, over 400,000 acres o f enhanced agricultural lands are needed to restore the depleted migratory waterfowl populations o f the Pacific flyway. Flooded rice fields are a key and integral part o f the successful restoration o f historic waterfowl and shorebird populations. 133 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7) W inter flooding o f rice fields provides significant waterfowl habitat benefits and should be especially encouraged in areas where there is minimal potential to impact salmon as a result o f surface w ater diversions. 8) An economically viable m arket fo r rice straw bales could result from the use o f rice straw bales in housing construction. 9) Existing regulatory requirements are costly and severely restrict the development o f straw-bale housing. 10) Statutory guidelines fo r the use o f straw-bale housing would significantly benefit low- cost housing, agriculture, and fisheries in California. b) I t is therefore, the intent o f the Legislature to adopt safety guidelines fo r the construction o f structures including, but not lim ited to , single-fam ily dwellings that use baled rice straw as a load-bearing o r non-load-bearing m aterial, provided that these guidelines shall not be effective w ithin any d ty or county unless and until the legislative body o f the city or county makes an express finding th a t the application o f these guidelines w ithin the d ty o r county is reasonably necessary because o f local conditions. 11.1.2 18944,31 a) Notwithstanding any other provision o f law, the guidelines established by this chapter shall not become operative w ithin any d ty or county unless and until the legislative body makes an express finding th a t the application o f these guidelines w ithin the d ty or county is reasonably necessary because o f local conditions and the d ty o r county files a copy o f th at finding w ith the departm ent b) In adopting ordinances o r regulations, a d ty or county may make any changes or modifications in the guidelines contained in this chapter as it determines are reasonably necessary because o f local conditions, provided the d ty or county files a copy o f the 134 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. changes o r modifications and the express findings fo r the changes or modifications with department. No change o r modification o f th a t type shall become effective or operative for any purpose until the finding and the change or m odification has been filed w ith the departm ent 11.1.3 18944.32 Nothing in this chapter shall be construed as an exemption from Chapter 3 commencing w ith Section 5500) of, o r Chapter 7 commencing w ith Section 6700) of, Division 3 o f the Business and Professions Code relative to preparation o f plans, drawings, specifications, or calculations under the direct supervision o f a licensed architect or civil engineer, fo r the construction o f structures th a t deviate from the conventional fram ing requirements for wood-frame construction. 11.1.4 18994.33 For the purposes o f this chapter, the following term s are defined as follows: a) Bale means rectangular compressed blocks o f rice straw, bound by strings or wire. b) Department; means the Department o f Housing and Community Development c) Flake; means slabs o f straw removed from an untied bale. Flakes are used to fill small gaps between the ends o f stacked bales. d) Laid fia t; refers to stacking bales so th at the sides w ith the largest cross-sectional area horizontal and the longest dimension o f this area is parallel w ith the w all plane. e) La id-on-edge; refers to stacking bales so th a t the sides w ith the largest cross-sectional area are vertical and the longest dimension o f this area is horizontal and parallel with the wall plane. 135 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0 Straw; means the dry stems o f cereal grains le ft after the seed heads have been removed. a) Subject to the availability o f funds, on o r before January 1, 2002, the California Building Standards Commission shall transm it, to the department and to the Legislature, a report regarding the implementation o f this chapter. b) The implementation report shall describe which cities and counties have utilized this chapter, and the number and type o f structures th a t have been built pursuant to local ordinances. The implementation report may include recommendations to amend the guidelines established by this chapter, or any other related m atters. c) The California Building Standards Commission may accept and use any funds provided or donated fo r the purposes o f this section 11,16 19994,35 a) Bales shall be rectangular in shape. b) Bales used w ithin a continuous w all shall be o f consistent height and w idth to ensure even distribution o f loads w ithin w all systems. c) Bales shall be bound w ith ties o f either polypropylene string o r baling wire. Bales w ith broken o r loose ties shall not be used unless the broken o r loose ties are replaced w ith ties, which restore the original degree o f compaction o f the bale. d) The moisture content o f bales, a t the tim e o f installation, shall not exceed 20 percent o f the total w eight o f the bale. Moisture content o f bales shall be determined through the use o f a suitable moisture m eter, designed fo r use w ith baled rice straw o r hay, equipped w ith a probe o f sufficient length to reach the center o f the bale, and used to 136 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. determine the average moisture content o f five bales randomly selected from the bales to be used. e) Bales in load bearing shall have a minimum calculated dry density o f 7.0 pounds per cubic foot. The calculated dry density shall be determined after reducing the actual bale weight by the weight o f the moisture content 0 Where custom-made partial bales are used, they shall be o f the same density, same string or wire tension, and, where possible, use the same number o f ties as the standard size bales. g ) Bales o f various types o f straw, including w heat rice, rye, barley, oats, and sim ilar plants, as determined by the building official, shall be acceptable if they meet the minimum requirements o f this chapter fo r density, shape, moisture content and ties. 11,1,7 1 8994,40 a) Straw-bale walls, when covered with plaster, drywall, or stucco, shall be deemed to have the equivalent fire resistive rating as wood-frame construction w ith the same w all- finishing system. b) Minimum bale wall thickness shall be 13 inches. c) Buildings w ith load bearing bale walls shall not exceed one story in height and the bale portion o f the load bearing walls shall not exceed a height-to-w idth ratio o f 5.6:1 for example, the maximum height fo r a wall th a t is 23 inches thick would be 10 feet 8 inches. d) The ratio o f unsupported wall length to thickness, fo r load bearing walls, shall not exceed 15.7:1 fo r example, fo r a wall that is 23 inches thick, the maximum unsupported length allowed is 30 fe e t 137 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. e) The allowable vertical live load and dead load on top o f load bearing walls shall not exceed 400 pounds per square foot, and the resultant load shall act a t the center o f the w all. Straw-bale structures shall be designed to withstand all vertical and horizontal loads as specified in the latest edition o f the Uniform Building Code. 0 Foundations shall be sized to accommodate the thickness o f the bale wall and the load created by the wall and roof live load and dead loads. Foundation o r stem walls which support bale walls shall extend to an elevation o f not less than 6 inches above adjacent ground a t all points. The minimum w idth o f the footing shall be the w idth o f the bale it supports, except that the bales may overhang the exterior edge o f the foundation by not more than 3 inches to accommodate rigid perim eter insulation. Footings shall extend a minimum o f 12 inches below natural, undisturbed soil, or to frost line, whichever is lower. g) 1) Vertical reinforcing bars w ith a minimum diam eter o f ’/z inch shall be embedded in the foundation to a minimum depth o f 7 inches, and shall extend above the foundation by a minimum o f 12 inches. These vertical bars shall be located along the centerline o f the bale w all, spaced not more than 2 feet apart. A vertical bar shall also be located along the centerline o f the bale w all, spaced not more than 2 feet apart. A vertical bar shall also be located w ithin 1 foot o f any opening or comer, except a t locations occupied by anchor bolts. 2) Nonbale walls abutting bale walls shall be attached by means o f one or more o f the follow ing methods o r by means o f an acceptable equivalent: (A) Wooden dowels o f 5/8 inch minimum diam eter and o f sufficient length to provide 12 inches o f penetration into the bale, driven through holes bored in the abutting wall stud, and spaced to provide one dowel connection per bale. 138 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (B) Pointed wooden stakes, a minimum o f 12 inches in length and 1 'h inches by 3 Vi inches a t the exposed end, fu lly driven into each course o f bales, as anchorage points. (C) Bolted or threaded rod connection o f the abutting w all, through the bale w all, to a steel nut and steel or plywood plate washer, a minimum o f 6 inches square and a minimum thickness o f 3/16 o f an inch for steel and to inch fo r plywood, in a minimum o f three locations. 3) (A) Load bearing bale walls shall be anchored to the foundation a t intervals o f 6 feet o r less. There shall be embedded in the foundation a minimum o f 2 Vi inch diam eter steel anchor bolts per w all, with one bolt located w ithin 36 inches o f each end o f each w all. Sections o f to inch diam eter threaded rod shall be connected to the anchor bolts, and to each other, by means o f threaded coupling nuts, and shall extend through the roof bearing assembly and be fastened w ith a steel washer and nut. (B) Bale walls and roof-bearing assemblies may be anchored to the foundation by means o f other methods, which are adequate to resist u p lift forces resulting from the design wind load. There shall be a minimum o f tw o points o f anchorage per w all, spaced not more than 6 feet apart, w ith one located w ithin 36 inches o f each end o f each w all. (D) W ith load bearing bale walls, the dead load o f the roof and ceiling systems w ill produce vertical compression o f the walls. Regardless o f the anchoring system used to attach the roof bearing assembly to the foundation, prior to installation o f wall finish materials, the nuts, straps, or cables shall be retightened to compensate fo r this compression. 139 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. h) 1) A moisture barrier shall be used between the top o f the foundation and the bottom o f the bale w all to prevent moisture from migrating through the foundation so as to come into contact w ith the bottom course o f bales. This barrier shall consist o f one o f the follow ing: (A) Cementitious waterproof coating (B) Type 30 asphalt fe lt over an asphalt emulsion (C) Sheet metal flashing, sealed a t join ts (D) Another building moisture barrier, as approved by the building official 2) All penetrations through the moisture barrier, as well as a ll joints in the barrier, shall be sealed w ith asphalt, caulking, o r an approved sealant. i) 1) For non load bearing walls, bales may be laid fla t or on edge. Bales in load bearing bale walls shall be laid fla t and be stacked in a running bond, where possible, with each bale overlapping the two bales beneath it. Overlaps shall be a minimum o f 12 inches. Gaps between the ends o f bales which are less than 6 inches in w idth may be fille d by an untied flake inserted smugly into the gap. 2) The firs t course o f bales shall be laid by impaling the bales on the rebar verticals and threaded rods, if any, extending from the foundation. When the fourth course has been laid, vertical #4 rebar pins, o r an acceptable equivalent, long enough to extend through all four courses, shall be driven down through the bales, two in each bale, located so that they do not pass through the space between the ends o f any tw o bales. The layout o f these rebar pins shall be approximate the layout o f the rebar pins extending from the foundation. As each subsequent course is laid, two pins, long enough to extend through tha t course and the three courses immediately below it, shall be driven down through each bale. This high, pinning method shall be 140 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. continued to the top o f the w all. In walls seven o r eight courses high, pinning at the fifth course may be eliminated. 3) Alternative pinning method: when the third course has been laid, vertical #4 rebar pins, or an acceptable equivalent, long enough to extend through a ll three courses, shall be driven down through the bales, two in each bale, located so th a t they do not pass through the space between the ends o f any two bales. The layout o f these rebar pins shall approximate the layout o f the rebar pins extending from the foundation. As each subsequent course is immediately below it, shall be driven down through each bale. This pinning method shall be continued to the top o f the w all. 4) Only fu ll length bales shall be used a t comers o f load bearing bale-walls. 5) Vertical #4 rebar pins, or an acceptable alternative, shall be located w ithin comers o f door openings. 6) Staples, made o f #3 or larger rebar formed into a ;U; shape, a minimum o f 18 inches long with two 6-inch legs, shall be used a t all comers o f every course, driven w ith one leg into the top o f each abutting comer bale. j) 1) All load bearing bale walls shall have a roof bearing assembly a t the top o f the walls to bear the roof load and to provide the means o f connecting the roof structure to the to the foundation. The roof bearing assembly shall be continuous along the tops o f load bearing bale walls. 2) An acceptable roof bearing assembly option consists o f tw o double 2-inch by 6- inch, o r larger, horizontal top plates, one located a t the inner edge o f the wall and other a t the outer edge. Connecting the two doubled top plates, and located horizontally and no more than 72 inches center to center, and as required to align w ith the threaded rods extending from the anchor bolts in the foundation. The 141 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. double 2-inch by 6-inch top plates shall be face-nailed w ith 16d nails staggered a t 16-inch o.c., with laps and intersections face-nailed w ith four 16d nails. The cross members shall be face-nailed to the top plates w ith four 16d nails a t each end. Corner connections shall include overlaps nailed as above or an acceptable equivalent, such as plywood gussets or metal plates. Alternatives to this roof bearing assembly option shall provide equal o r greater vertical rigidity and provide horizontal rigidity equivalent to a continuous double 2 by 4 top plate. 3) The connection o f roof fram ing members to the roof plate shall comply w ith the appropriate sections o f the California Building Code, k) All openings in load bearing bale walls shall be a minimum o f one fu ll bale length from any outside comer, unless exceptions are approved by an engineer or architect licensed by the state to practice. Wall or roof load present above any opening shall be carried, or transferred, to the bales below by one o f the following: 1) A frame, such as structural window or doorframe 2) A lintel, such as an angle-iron cradle, wooden beam, or wooden box beam. Lintels shall be a t least tw ice as long as the opening is wide and extend a minimum o f 24 inches beyond either side o f the opening. Lintels shall be centered over openings. 3) A roof bearing assembly designed to act as a rigid beam over the opening. I) 1) All weather-exposed bale walls shall be protected from water damage. However, nonbreathing moisture barriers shall not be used on the upper tw o-thirds o f vertical exterior surfaces o f bale walls in order to allow natural transpiration o f moisture from the bales. 2) Bale walls shall have special moisture protection provided a t all windowsills. Unless protected by a roof, the tops o f walls shall also be protected. This 142 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. moisture protection shall consist o f a w aterproof membrane, such as asphalt- impregnated felt-paper, polyethylene sheeting, o r other moisture barrier, as approved by the building official, installed in a manner that w ill prevent w ater from entering the wall system a t windowsills or at the tops o f walls, m) 1) Interior and exterior surfaces o f bale walls shall be protected from mechanical damage, flames, animals, and prolonged exposure to water. Bale walls adjacent to bath and shower enclosures shall be protected by a moisture barrier. 2) Cement stucco shall be reinforced w ith galvanized woven wire stucco netting o r an equivalent, as approved by the building official. The reinforcement shall be secured by attachm ent through the wall a t a maximum spacing o f 24 inches horizontally and 16 inches vertically. 3) Where bales abut other materials, the plaster or stucco shall be reinforced w ith galvanized expanded metal lath, or an acceptable equivalent, extending a minimum o f 6 inches onto the bales. 4) Earthen and lime-based plasters may be applied directly onto bale walls w ithout reinforcement, except where applied over the materials other than straw. n) 1) All wiring w ithin or on bale walls shall meet a ll provisions o f the California Electrical Code. Type; NM; or; UF; cable may be used, or wiring may be run in m etallic or nonm etallic conduit systems. 2) Electrical boxes shall be securely attached to wooden stakes driven a minimum o f 12 inches into the bales, or an acceptable equivalent o) Water or gas pipes w ithin bale walls shall be encased in a continuous pipe sleeve to prevent isolated from the bales by a moisture barrier. 1 Ed it e d b y Ke lly Lemer a nd Pa me la Wa d s w o rt h G o o d e, The B ui ld in g Offi ci al ' s Gu ide to St raw- bal e Cons t r uc t ion. V e rs ion 2.1 (pub l i s he d b y The St raw B u ild in g Asso ciatio n © 2000) pp. 3*10 143 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

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Asset Metadata

Creator Sabavala, Nazneen (author)

Core Title Thermal performance of straw bales

Degree Master of Building Science / Master in Biomedical Sciences

Degree Program Building Science

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Architecture,engineering, mechanical,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-43791

Unique identifier UC11341834

Identifier 1409603.pdf (filename),usctheses-c16-43791 (legacy record id)

Legacy Identifier 1409603.pdf

Dmrecord 43791

Document Type Thesis

Rights Sabavala, Nazneen

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA