Time To Give Straw Another Look - Arkin Tilt

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Time to give straw another lookTime to GiveStraw Another LookInnovative new ways to build low-carbon homes witha time-tested and well-known renewable resourceBy David arkinMention straw-bale construction, and,while many have heard of it, themajority of people still reply withskepticism: “Won’t it rot?” “Doesn’tit burn?” “What about insects, moisture, airtightness ?” and the list goes on.Despite much testing, a proven track record,relative ease to build with, and examples ofdurability from buildings over 100-years-old, strawbale construction hasn’t achieved the widespreadpopularity it seems destined to reach. Withinclusion in the International Residential Code (IRC)in 2015, a long list of benefits (read on), and a roleto play in helping to solve global climate change,straw as a building material is in the news again.Photo courtesy of New FrameworksOwing to its renewed success—and the point ofthis article—are the many new and varied ways tobuild with straw. But first, a quick recap for thosewho are reading about straw-bale construction forthe first time.History and benefits of straw-bale buildingStraw-bale construction emerged in the late 1800s,in the Sandhills region of Nebraska, where treeswere scarce and the soils not suitable for buildingthe prairie-sod homes many pioneers of theGreat Plains favored. A clever individual startedstacking the big fuzzy bricks from newly inventedbaling equipment, and strawbale construction wasborn. Like both democracy and jazz, this uniquelygreenbuildingadvisor.com1

Time to give straw another lookDesigned for California’s wildfire country, this 872-sq.-ft. cabin is a hybrid straw-bale home. That means that while some ofthe walls are conventionally built with dimensional lumber and the roof is made of SIPS, the rest is built with straw-baleconstruction techniques.American innovation has been exported aroundthe world.Straw bale’s modern revival can be traced to a1984 article in Fine Homebuilding magazine byGary Strang about a straw-bale studio built by JonHammond, a young architect in Davis, California,who had built the small structure on his family’sfarm. Enthusiasts Matts Myhrman, the late JudyKnox, and others made a pilgrimage to Nebraska,and in turn traveled the country teachingworkshops and promoting the many benefits ofstraw-bale construction.“What I wanted to be doing was inspiring deepchange. Little did I know, for the first year or two,what a transformational vehicle we had by the tailand that straw-bale construction would become aPhoto courtesy of Eric Millettephenomenon touching the lives of individuals andgroups throughout the world,” said Judy Knox.The benefits of straw bale construction are widelyknown but worth enumerating again, if briefly: H igh insulation values: Depending on thickness,straw-bale walls can easily achieve R-30. Thermal-mass properties: Straw-bale wallscommonly have a 12-hour thermal transfer rateto the middle of the wall. Affordability: Straw bales are an affordableinsulator and construction does not require asuper high skill level. In fact it is is accessible todo-it-yourselfers. Nontoxic, safe, and healthy constructionprocess: No PPE required!greenbuildingadvisor.com2

Time to give straw another look P art of healthy indoor-air quality (IAQ):Generally natural finishes are used on strawbale walls, including lime plaster, clay, andother nontoxic, no-VOC, or otherwise other offgassing compounds. Humidity control: Straw has a remarkablecapacity to hold and release moisture withoutthe risk of mold growth. Clay plaster finishes, inparticular, are also hygroscopic, meaning theyabsorb and release moisture naturally as well. Thick walls: Deep window and door openingsare aesthetically pleasing and offer designopportunities for storage, seating, etc. Agricultural by-product: Straw is availablelocally nearly everywhere. Annually renewable: Unlike trees, which mayneed 40 years to mature, straw is grown andcan be harvested in one season. Acoustic performance: Due to the inherentmass of the walls, straw-bale homes are knownto be quiet. Structural integrity: Plastered straw-bale wallscan be stronger than plywood shear walls. Tested and proven fire resistance: Designedright, straw-bale walls can have a two-hour firerating when finished with lime plaster. Airtightness: Just like houses insulated withother air-permeable insulation, straw-balehomes can achieve Passive House levels ofairtightness when built to do so. Stores carbon: Here’s the data: 1.62 lb. of CO2per lb. of straw (2000-sq.-ft. home 10.5 tons).Taking straw bale mainstreamIn the early days of straw-bale building, baleswere stacked and pinned, first with rebar in themiddle, and later with bamboo on the surface.Innovation quickly led designers and builders topost-and-beam structures supporting the upperfloors and roof, with the bales infilled between theframing. In this type of construction, pinning couldbe eliminated.A testing regimen led by Bruce King, P.E., of theEcological Building Network and members of theCalifornia Straw Building Association (CASBA)answered many concerns and ultimately led to theadoption of Appendix S in the IRC. Many bookshave now been written on the topic of buildingwith bales, most recently CASBA’s “Straw BaleBuilding Details,” an illustrated guide for buildingwith straw in its baled form.Straw bales gained popularity in the 1990s andearly 2000s, and while it hasn’t waned, it hasn’tgrown substantially either. As a co-director ofCASBA and an enthusiastic proponent of thetechnology, I’ve been searching for an answer as towhy. One is likely a lack of general awareness, andanother a knee-jerk reaction (often blamed on thefirst little pig) that straw is not a suitable buildingmaterial; or that it's difficult to get a permit (eventhough it’s now in the building code); or that it’sonly for poor people; or only for rich people; or onlyfor those targeting the pinnacle of green building.Another reason straw-bale construction has notmade it to the mainstream could be a perceptionthat straw homes must have lumpy walls withrounded corners and other Hobbit-like details,even though a number of architects and designershave created handsome modern structures,utilizing bale walls for higher efficiency that allowsfor greater use of glass without paying an energyperformance penalty (see photo above).As Matts likes to say, “you can do anything withstraw bales, except have skinny walls,” thoughthat’s changing too. Our firm has created manyaward-winning straw-bale buldings, including FineHomebuilding’s Best New Home of 2012, “SantaCruz Straw Bale.”But perhaps the biggest factor limiting growthof straw-bale construction is that it isn’t readilyavailable as a building product—one that can bespecified from a manufacturer, let alone purchasedat a local supply yard. Even though wood literallygrows on trees, nearly all of it is purchased froma lumber yard, and in many cases in a highlyprocessed and value-added form. And this is thecase for nearly all building materials—one doesnot make their own gypsum board, for example,or concrete blocks, or nearly anything else, oftenthings that could be made from locally availableand often inexpensive (if not free) resources.Builders and designers are risk-averse,understandably so, and use of manufacturedproducts in accordance with the manufacturer’srecommendations shifts some responsibility tothe product’s source should something go wrong.A farmer is not taking any liability if somethinggoes wrong with the bale of straw you boughtgreenbuildingadvisor.com3

Time to give straw another lookThe ModCell Bale Housefrom them. Keeping the straw dry—and thereforeeffective—falls entirely on the designers, builders,and owners, and this burden of responsibility haslikely kept the many benefits of straw largely outof production home building or other uses of itat scale.However, the past few years have seen anemergence of several new ways to build withstraw, lessening the perceived risk or constructioncomplexities, and in a few cases actual productsare coming onto the market. Here are some of themost exciting innovations and developments.A prefab, straw-insulatedpanel from EcoCoconPanelized wall systemsModCell is a UK-based company that pioneeredprefabricated wall systems with the Bale Houseat the University of Bath in 2009, and has broughtits panelized bale walls to several larger-scalemultifamily and commercial projects since then.Chris Magwood of the Endeavour Centrein Peterborough, Ontario, built an affordablehousing project utilizing a panelized wall system,Top photo courtesy of ModCell. Bottom right photo courtesy of EcoCocon.and wrote about it in “Essential Prefab Straw BaleConstruction,” Like ModCell, they promote theability to assemble panels in a climate-controlledsetting, and then deliver them to the job siteprefinished, craning them into place.greenbuildingadvisor.com4

Time to give straw another lookInsulating a stick-framed, mixed-usebuilding with straw balesThe finished building, designedby the author’s firmEcococon, represented in the U.S. by BuildWith Nature, is a timber and straw wall-panelsystem that is computer- and factory-generatedfor quick and easy assembly on the job site, andthen finished in place. They have completed theirfirst home in North America, in upstate NewYork, and are looking to expand operations with aproduction facility somewhere in the states.Straw bales as insulation onlyThe straw-bale construction appendix in the IRCmentions the use of straw bales placed “on-end,”which was contemplating their use as insulationbetween standard 2x wood framing, a concept firstconceived by architect Daniel Smith of Berkeley,California. Placement of approximately 23-in.wide bales between 2 6 studs at 24 in. on centerhas been proven feasible in both residential andcommercial projects.We took this approach on a 34,000-sq.-ft. mixeduse building constructed in Eugene, Oregon, for 175 per square foot. Vapor-permeable plywoodwall sheathing (not OSB) is utilized on the exterior,along with a highly permeable weather barrier andnearly any finish material.Jacob Deva Racusin of New FrameworksNatural Building created a similar hybrid wallsystem by stacking straw bales to the interior ofPhotos top left and right courtesy of author. Bottom right photo courtesy of New Frameworks.With Racusin and New Frameworks’ hybrid strawbale approach, the bales can be installed beforethe dense-pack cellulose is blown into the walls, asseen here, or after, as seen in the photo at the topof the article.greenbuildingadvisor.com5

Time to give straw another lookUpdating an existing home withstraw-bale insulation2 4 framed walls filled with cellulose insulation.The exterior can be finished conventionally withcommon sheathing and siding materials, but incombination with the straw insulation one can buildan affordable high-performance wall in the mostextreme climates—Jacob built in the Northeast.Many older homes are woefully underinsulated,having been built at a time when energy was cheapand we simply didn’t understand the negativeimpacts the operating energy of a home canhave. Many are drafty and uncomfortably cold orhot, depending on the location and time of year.Retrofitting straw bales can drastically improvethese homes.When I was a boy in Wisconsin, we’d place a rowof bales around the exposed foundation walls ofour old farmhouse every fall to keep the pipes inthe basement from freezing; this is not a new idea.Matts Myrhman wrapped a concrete-block house inArizona with bales in the 1990s, and a tin barn caféin Texas was given a similar retrofit.More recently our firm wrapped part of amidcentury-modern home in Palo Alto, California,with straw bales, and architect Bob Theis workedwith CASBA co-director Massey Burke andworkshop volunteers wrapping a ranch-style homein El Sobrante; both yielded vastly increasedcomfort and performance—as well as an aestheticupgrade—for the homeowners.A seven-story affordable housing project inSt. Die, France, was built with straw bales placedPhoto courtesy of the authorin particleboard modules and craned against thecross-laminated timber (CLT) walls. These panelswere wrapped and finished with ceramic tiles.Overall the project stores an impressive amountof carbon—largely in the wood, but also in thestraw—relative to the concrete and steel thatwould have been used.Sheathing products made from strawOver the past 30 years, we’ve seen a number ofsheet products made from straw come and go.Among these was Meadowboard, from pressedrye grass and cyanurate glue, and Wheatboard,a similar product made from wheat, and othersincorporating plant fibers.Leading the return to plant-based board productsis Calplant1, a medium-density fiberboard (MDF)of rice straw, soon starting production at its newfactory near Winters, California. It promises to bea direct substitute for wood-based MDF, at ascale that’s sure to impact the market, as MDF isubiquitous in building products such as cabinets,trim, flooring substrates, and more.While straw in its baled form is largely noted forits insulation value, there are many ways to utilizeit in non-baled form, and an Austrian company hasdevised a means of shredding straw for use as ablown-in insulation product. We hope to see thisavailable North America soon.Compressing agricultural fibers to formcompressed straw board (CSB) was discoveredgreenbuildingadvisor.com6

Time to give straw another lookfound in the current IRC. Straw, however, is notthe only plant-based building material, and I thinkwe will continue to see this category grow incoming years.Hempcrete has generated a fair amount of buzz(pardon the pun) lately, utilizing the starchy hurd,the center of the stalk, chopped and coated in alime binder. Bamboo in the form of BamCore, astud-free wall system that can be infilled with anyinsulation to a climate-appropriate wall thicknesswith minimal thermal bridging, is now availabletoo. Both of these are carbon-storing, rapidlyrenewable, and plant-based.Bottom lineStraw MDF with arouted edge fromCalplant1in Sweden in 1933. Known as Stramit Board, itwas exported to the UK in 1945 and to Australiain 1954. Also referred to over the years asDurra, Prestowall, Agriboard, Ortech, Ligni-cell,Kodu Kuubis and others, CSB is formed by theapplication of heat and pressure to cellulosematerials. Heat causes naturally present moistureto be turned to steam. The lignin which forms 25%of cell walls of all plants is liquified and the longchain molecules act as a bonding agent. Pressureforces the materials together into a self-bondedwhole, thus straw becomes a load-bearing board.Common in Australia, we look forward to CSB’sreturn to this continent soon.Plant-based, beyond strawMany building methodologies, historically and tothis day, employed straw as a component. Adobeconstruction has been accepted in the buildingcode since the 1940s and is a traditional methodof making sundried bricks of clay and straw. Lightstraw clay (LSC) utilizes these same materials butin a higher concentration of straw, using a clayslip (watery clay) to coat the straw for greaterdurability, similar to the wattle and daub of yore.Straw is an additive to clay plasters, a means offiber reinforcement not unlike the way horse hairwas added to plaster in the past.Both Appendix R—Light Straw Clay—andAppendix S—Straw Bale Construction—can bePhoto courtesy of the manufacturerWood has long dominated the residential buildingworld, and for good reason. It’s natural, reasonablydurable, easy to work with, and beautiful. In therush to minimize the carbon footprint of buildings,wood in the form of heavy timber, cross-laminatedtimber, mass plywood panels, and other woodbased products has emerged as some of the bestalternatives to concrete and steel. It may soon be aviable alternative to some of the less-than-climatefriendly insulation materials used today as well. Butthe impacts on our forests (and their soil health,where carbon is stored) cannot be ignored.Rapidly-renewable resources including bamboo,hemp, mycelium, and, of course, straw are betterchoices for drawing down carbon. The buildingindustry is budding with new, innovative lowcarbon options for us to design and build with ina climate-responsible way. Traditional straw-balebuilding remains a viable option too. CASBA’snew guide provides all the background informationas well as pertinent details to undertakeconstruction of a straw-bale home. If there wereever a time to give these material another look,that time is now.To re-frame for builders what Michael Pollanlanded on as the most simple rules for eating well:Build shelter, not too big, from mostly plants.Though in the case of these biogenic resources,using more instead of less could actually be agood thing.David Arkin, AIA, LEED AP, is co-director ofCASBA and, along with his wife Anni Tilt, AIA, aprincipal of Arkin Tilt Architects.greenbuildingadvisor.com7

1984 article in Fine Homebuilding magazine by Gary Strang about a straw-bale studio built by Jon Hammond, a young architect in Davis, California, who had built the small structure on his family’s farm. Enthusiasts Matts Myhrman, the late Judy Knox, and others made a pilgrima