Green Means
Straw Bale Homes Hit Mainstream
By Shannon Scott
Early Nebraska settlers were the first straw bale builders in the U.S. The early sod huts didn’t insulate or protect prairie homes too well, but when mixed with large amounts of straw – voila!
In grain growing areas where straw was a common leftover from harvests, straw became a popular building material especially after steam powered bailers came on the scene. Baled homes were relatively common up until the 1950s when assembly line construction materials became more broadly available.
In the early 1970s, as fuel prices escalated, developed societies began demanding more energy efficient, less toxic homes. Cheap and readily available with high r-value insular qualities, straw bale building saw resurgence.
Universities and construction professionals conducted r-value, shear strength and other structural integrity tests on individual straw bales and completed baled structures. Well conducted, valid studies provided proof that bale homes were in fact structurally sound and more energy efficient than the common framed homes of modern decades.
Load Bearing and Non-load Bearing
Structurally speaking there are two types of straw bale homes, load bearing and non-load bearing. Load bearing refers to how the roof weight is supported and transferred down to the foundation. Load bearing straw bale homes bear the roof load on the bales themselves. Non-load bearing homes use modified post and beam or more traditional post and beam construction to support roof weight.
Modified post and beam style utilizes two-by dimensional lumber nailed to plywood sheaths cut the width of the bales. The “posts” run from the upper portion of the foundation to a top plate, “beam” spanning across the top of baled walls. All-threads, anchored in the foundation, impaled through bales, and cinched down on the top plates, compact bales and distribute the roof load resting upon the top plates down to the foundation.
Moisture
Moisture is a straw bale’s enemy. With what we now know about harmful molds to human health, excessive moisture buildup has become a concern to all. Two key considerations when designing and building a straw bale home are to keep the bales up and covered. Design so that lower portions of bale walls are up from the grade of the surrounding land, so snow packs or rain cannot accumulate against them. Bales must be kept covered with adequate porch or roof overhangs so that water cannot rest atop walls.
During construction, bales must be kept dry, protected from the elements with tarps. Once walls are built, make sure they stay covered until exterior finish is applied.
Below left: A modified post and beam garage with bales well protected until plastered or finished. Notice that straw bales rest 2 feet above grade on well tarred and sealed concrete blocks, so that snow loads will never accumulate against bales and so that condensation will not permeate from cold concrete up into the bottom of bales.
Below right: A post and beam exoskeleton design. The wrap-around porch 2 feet above grade ensures driving rains and snow loads don’t get near walls. Like with the garage photo, bales are covered with heavy gauge tarps before exterior finish.
Noise
Straw bale homes provide superior noise reduction from the outside world. Of course window placement and other factors affect interior sound, but generally the thick walls not only insulate from heat and cold, but noise as well.
More Fire Proof
Contrary to what many believe, straw bale homes are more fire resistant than conventional homes. Studies show that straw bale homes typically have three times the fire resistance of a standard framed home. A conventional framed wall has plenty of air space between framing studs. Once a fire breaks through paper sheathed sheetrock, houses go up in flames quickly. Since straw bales are dense, compressed tightly, and sealed with multiple layers of lime plaster, stucco, or other interior and exterior wall finishes it’s darn tough to get them to burn.
Aesthetics
Straw bale structures lend themselves to artful design. Straw can be rounded, finished with undulations in the exterior and interior spaces, and lends easily to window seats. Thick walls make inhabitants feel more protected from the outside world. They look solid, feel solid, and are much stouter than typical framed buildings.
Healthier
Finishing interior walls with natural clay plaster allows any moisture in the home to move in and out of the wall’s porous surface. This infuses interior environments with negative ions. Negative ions are odorless, tasteless, and invisible molecules that we ingest in heavy quantities in particular environments: beaches, near waterfalls, and during thunder storms. Negative ions are thought to elevate serotonin levels that fight off the blues, making us feel good.
“Negative ions increase flow of oxygen to the brain. This results in less sleepiness and greater mental energy”, according to Pierce Howard, PhD and author of The Owners Manual for the Brain: Everyday Applications from Mind Brain Research. Negative ions may also protect against particulates that irritate mucous membranes making us sneeze and cough. Of course, clay can be applied to sheet rock surfaces as well, but feels and looks richer on thick straw walls.
Green Choices
Green living means sustainable lifestyle choices. Plan well to reduce waste, maximize energy efficiency, and be conscience of your home’s environmental impact. There are many green and sustainable options available now, but straw bale still leads as one of the more interesting, user-friendly, and aesthetically pleasing options.
If you have always been curious about straw bale homes or are in designing/planning stages drop me an e-mail. I’d be happy to answer questions or offer tips on what to do and avoid. I’ll also be offering a green building course though Great Basin College’s Community Education program in late winter. For anyone interested, registration is through the college. The class should prove fun, informative and includes a tour of the straw bale home pictured in this article.
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