The Last Straw? Hardly!
Building with a Renewable Resource
By Anni Tilt and David Arkin, Arkin Tilt Architects
Mention straw bale construction, and while many have heard of it, the majority of people still reply with skepticism. “Won’t it rot? Doesn’t it burn? What about insects / moisture / air-tightness / etc.?” In spite of much testing, a proven track record, relative ease to build with, and examples of buildings over 100 years old, it hasn’t achieved the widespread popularity it seemed destined to have. However, with inclusion in the International Residential Code in 2015, a long list of benefits (read on), and a role to play in helping to solve global climate change, building with straw is in the news again.
First, a quick recap: Straw Bale Building emerged in the late 1800s in the Sandhills region of Nebraska where trees were scarce and the soils were not suitable for building the prairie-sod homes many pioneers of the Great Plains favored. One clever individual started stacking the big fuzzy bricks from newly-invented baling equipment, and thus, straw bale construction was born. Like democracy and jazz, this uniquely American innovation has since been exported around the world. Its modern revival can be traced to a 1984 article in Fine Homebuilding magazine by Jon Hammond, a young architect in Davis, California, who had built a small structure on his family’s farm. Enthusiasts Matts Myhrman, the late Judy Knox, and others made a pilgrimage to Nebraska and in turn traveled the country teaching workshops on straw bale construction and promoting its many benefits.
“What I wanted to be doing was inspiring deep change. Little did I know, for the first year or two, what a transformational vehicle we had by the tail and that straw bale construction would become a phenomenon touching the lives of individuals and groups throughout the world." —Judy Knox
The benefits of straw bale construction are many:
High Insulation Values – walls of at least R-30 thermal resistance
Excellent Thermal Properties – 12-hour thermal transfer to middle of wall
Nontoxic, safe and healthy – no PPE required
Good indoor air quality and humidity control
Agricultural by-product – available locally nearly everywhere
Annually renewable – unlike trees needing ±40 years to mature
Acoustic performance – quiet with a feeling of solidity
Structural integrity – can be stronger than plywood shear walls
Tested and proven fire resistance – 2-hour fire rating for lime plaster
Airtightness – has achieved Passive House standards
Affordable and accessible to do-it-yourselfers – and FUN!
Thick wall aesthetics – deep window and door openings
Stores Carbon – 1.62 lbs. of CO2 per lb. of straw (2000 sf home = 10.5 tons)
One of the major barriers had been that straw bale construction wasn’t among the allowed means of construction in most Building Codes, restricting access to building permits, financing, and insurance. A testing regimen led by Bruce King, P.E., of the Ecological Building Network, and other members of the California Straw Building Association answered many concerns and ultimately led to inclusion of straw bale construction into the International Residential Code (Appendix S), clearing the path for adoption by jurisdictions around the globe. It was adopted into the California Residential Code in 2016. The building code language with commentary can be downloaded from the CASBA website at no cost. Many books have now been written on the topic of building with bales, most recently CASBA’s ‘Straw Bale Building Details,’ an illustrated guide for building with straw in its baled form.
Straw bale construction grew in popularity in the 1990s and early 2000s, and while it hasn’t waned, it hasn’t grown substantially either. What are the reasons? Possibly a lack of general awareness, or a knee-jerk reaction (often blamed on the first little pig) that straw is not a suitable building material. Or that it is difficult to get a permit (even though it’s now in the Building Code). Or that it’s only for poor people. Or only for rich people. Or only for those targeting the pinnacle of ‘green building.’
Another could be a perception that straw homes must have Hobbit-like details, even though a number of architects and designers have created handsome modern structures, utilizing bale walls for higher efficiency which allows for greater use of glass without paying an energy performance penalty. Arkin Tilt Architects has created many award-winning strawbale buildings, including Fine Homebuilding’s ‘Best New Home’ of 2012.
“A straw bale home has been part of my life for over 20 years. It is the stillness and the “at peace” feeling that it engenders, which I have found to be most appealing. After all these years of strenuous weather and winds, the solidness and stillness of the house remains undisturbed. The wood and stone homes around me have not fared as well.”
-- Suzanne Johnson, straw bale homeowner
Perhaps the biggest factor limiting the growth of straw as a construction material is its unprocessed nature: it cannot be specified from a manufacturer, let alone purchased at a local supply yard. Even though wood literally grows on trees, nearly all of it is purchased from a lumber yard, and in many cases in a highly processed and value-added form. And this is the case for nearly all building materials; one does not make their own sheetrock out of gypsum, for example, or concrete blocks, or nearly anything else, regardless of the availability of natural resources.
Builders and designers are risk-averse, understandably so, and the use of manufactured products (in accordance with the manufacturer’s recommendations) shifts some responsibility to the product’s source, should something go wrong. A farmer is not taking any liability if something goes wrong with the bale of straw you bought from them. Keeping the straw dry—and therefore effective—falls entirely on the designers, builders and owners of these wonderful homes, and this burden of responsibility has likely kept its many benefits largely out of production home building or other uses of it at scale.
However, the past few years have seen an emergence of several new ways to build with straw, lessening the perceived risk or construction complexities, and in a few cases actual products are coming onto the market. These range from panelized straw wall systems such as ModCell or EcoCocon (largely available in Europe, with some representation in the US), to straw fiberboards that rival their wood-based cousins, with production based squarely in California’s rice-growing Central Valley.
The role of embodied carbon has given straw another critical advantage: building with straw (and other plant-based rapidly renewable materials) addresses climate change – the existential crisis of our generation – by building net-zero carbon or even carbon-sequestering buildings. While there is finally substantial interest (and code-mandate) in the energy efficiency of the built environment, the embodied carbon of building products and construction represent 11% of global emissions. Over the crucial next 10 year period, the embodied carbon of new construction will far exceed the operational carbon of those buildings. See New Buildings: Embodied Carbon – Architecture 2030 Straw not only requires minimal energy (transportation and processing), it also stores a substantial amount of carbon, which is absorbed in the growing process via photosynthesis.
Finally, the ability of plastered straw bale walls to survive wildfires should make everyone sit up and pay attention. Arkin Tilt Architects has had 4 bale projects survive wildfires in the past 4 years where many of their neighbors' homes burned. That is a pretty powerful testimonial, and should keep away the “wolf” of a changing California climate.
Arkin Tilt Architects is an award-winning firm specializing in energy and resource efficient design. Their projects embody a marriage of thoughtful design and ecology, creating spaces that are comfortable and lyrical. They pay particular attention to the integration of the built and natural environments – from siting to careful detailing. They have extensive experience with alternative construction systems including straw bale and rammed earth, renewable energy systems, greywater, and non-toxic and recycled materials.
Many Berkeley architects and engineers have been instrumental in their advocacy of straw bale construction, most notably CASBA’s code efforts led by Martin Hammer.
The AIA East Bay will be featuring a straw bale ADU in Berkeley on an upcoming home tour. Review their site for details.