Good feelings emerge
when people work together
on straw-bale homes


Straw-Bale Home Building - Some Lessons Learned

by Catherine Wanek / StrawHomes.com

A wonderful irony about straw-bale builders is that they often started out as complete skeptics. Doesn't it rot? Doesn't it burn? What about the Big Bad Wolf? We converts who've heard this before have learned to smile patiently. After all, it was just a decade ago that modern-day pioneers seeking affordable, ecological, beautiful housing built the first code-approved straw-bale homes, and now they are in every state and all over the world. It's likely that this Doubting Thomas will soon be converted to a grinning, wide-eyed natural builder, by the amazing potential of the humble bale.

Individually, a stalk of straw seems fragile, but hundreds together, compressed and baled, make a sturdy building block. Stack a bunch of these blocks together and walls can go up in a hurry - especially if you enlist your family and friends to help. Roof and plaster it, and you have a super-insulated house; the concept is simple and intuitive. And straw bales, soft and sculptable, can be shaped into cozy spaces, forming a home that feels like an embrace.

This home not only feels good, but you can feel good about it -- straw is commonly underutilized, composted or burned as an agricultural waste product. The staff of the staff of life, straw is available at a cheap price where ever grain is grown. And stacked like giant bricks to form a thick wall, bales offer super insulation from the heat or cold or noise outside, providing a quiet, comfortable living space with modest life-time energy requirements. Replacing "stick frame" walls with bales can cut by half the amount of timber needed in a modern home, reducing demand on forest resources.

Unlike manufactured insulation materials, straw is natural and non-toxic, and very low in "embodied energy" -- the energy required to process and deliver a material to a building site. Should a fire get started, lab tests and experience have shown that foam insulations ignite at low temperatures and release poisonous fumes, and wood studs and trim will burn readily. But bales, compressed and sealed with plaster, are starved of oxygen and resist combustion. If they do catch on fire, they merely smolder, allowing precious time for occupants to exit and help to arrive.

Building with bales also has the potential to impact "global warming," by significantly reducing fossil fuel consumption. Preliminary studies in China and Mongolia indicate that each straw-bale home built there, over a projected 30-year life (and they should last much longer), will reduce the amount of carbon entering the atmosphere by 150 tons. Combined with China's locally-available supplies of straw, bale-building technology holds out the promise of affordable, ecological housing to literally billions of people.

Good Design and Detailing

To live up to its promise, straw-bale building systems must be understood and optimized. The number-one nemesis of straw is water, the universal solvent. Exposed to above 20% moisture content (about 80% relative humidity), bales will support fungal growth and begin to decompose. Wet bales have also been linked to insect infestations, which disappear as the bales dry out. Conversely, kept perfectly dry, straw can remain inert for centuries, even millennia. It's not surprising that appropriate bale-building design is consistent with good design practice for homes in general.

A well-designed roof and foundation ("hat and shoes") will prevent most problems with moisture in bale structures. Raising straw-bales 6" - 10" (15-25cm) above grade and installing a moisture barrier (or "damp-proof course") between the stem-wall and first course of bales should eliminate moisture wicking up from the ground. It's also wise to create a "toe-up" for straw-bales, above the final floor level in case of interior flooding from a plumbing problem.

A roof design that incorporates wide eaves (2 -3' if possible) is also highly recommended. Not only will it shed rain and snow far from bale walls, but it will protect earthen plasters from erosion and cement stucco from becoming water saturated. Additionally wide overhangs, portals and porches offer the cheapest living/storage space possible, and are useful in any climate. Flat roofs and parapet walls, common in the Southwest, are not recommended. Unless their detailing and maintenance is impeccable they will eventually leak, causing problems no matter what your wall system.

Good window detailing is also critical to avoid moisture infiltration. Commonly, windows are set all the way to the outside of an opening, leaving a bale-wide shelf or window-seat on the inside, and the minimum surface needing protection from the weather outside. Where window ledges are exposed, proper flashing is essential, and a "drip edge" recommended.

Earthen Plasters and Stucco

Finish plasters serve multiple functions. Protecting straw-bale walls from wind and rain, they also seal bales from birds and rodents that find them to be an attractive home too. Plasters add structural strength to the wall -- especially cement-based stuccos. In laboratory tests, compression strength, wind resistance, and racking sheer strength were significantly enhanced after stucco was applied, irrespective of whether wire mesh was used. However, in seismically-active areas, a bale/stucco/wire-mesh structural combination is recommended - where it has shown great promise as a safe building system.

It's also important to plaster both sides of a straw-bale wall for fire resistance, to seal out oxygen. For example, if a an interior wall were "furred out" with studs to attach drywall, without plastering it first, the resulting air space would act as a chimney in case of a fire. A well-sealed bale wall is also critical for energy-efficiency, as even minor gaps will allow air infiltration through the porous bale, reducing its effective R-value.

Conventional builders often want to add an air-barrier (Tyvek and the like) to the outside of a bale wall, under the exterior plaster, to eliminate air infiltration. This is not only unnecessary -- as a well-detailed plaster is sufficient for this purpose -- but can be a critical mistake. Such an air barrier will prevent the exterior plaster from "keying in," or bonding to the straw bales, reducing the wall's structural strength. Worse yet, as interior water vapor migrates to the colder exterior through the straw-bale wall, it will tend to condense on the inside of this air barrier. This moisture will dry out very slowly, and when the temperature warms, it can produce conditions ripe for fungal growth.

To optimize the thermal performance of straw-bale wall systems, it's useful to remember that most heat loss and gain is through the roof. Without ceiling insulation, a straw-bale house is like a thermos bottle without a lid. Whatever insulation you choose, air infiltration will significantly compromise its performance, so take care to seal any cracks, especially the joint where the walls meet the ceiling. If bales are used as roof insulation, space the trusses or rafters so the bales fit tightly together. It is also wise to plaster any exposed surface, as a fire-retarding measure. An earthen slip should be adequate, but be sure it dries out fully.

In cold climates, floors and foundations should also be insulated from the ground and outside air. Incorporating passive-solar design provides free heat from the sun, which is stored in interior mass floors, walls, and objects. Thermal mass materials equalize to their surrounding air temperatures gradually, tending to moderate the climate around them. A thick plaster on straw-bale interior walls adds up to provide a significant part of thermal mass required for effective solar design. Earthen plasters will also moderate humidity inside homes, providing the perfect range for human health, according to baubiologists. Praised for absorbing odors and softening sounds, plasters of earth are also renowned for their beauty.

Earthen plasters have an added advantage of being hydrophilic, which means that they will always wick moisture from straw, acting to protect it from rot. Historical examples are English and Welsh cob houses and German straw-clay infill walls, many of which are still lived in today after centuries of use. It appears that clay combined with straw has a preservative effect, and is much less vulnerable to moisture. Earthen plasters on straw-bale walls may also have this kind of long-term beneficial effect.

Post-and-Beam versus Load-bearing

A modest single-story rectangular building lends itself to load-bearing design, and will generally be cheaper to build than a post-and-beam-and-bale structure, primarily through reduced lumber costs. Load-bearing bale walls can generally be erected faster, too, as they avoid the inevitable interface with the structural system. Both modern testing and the historic Nebraskan homes indicate that bales are sturdy building blocks that can bear the roof load and stand the test of time in a well-built house.

Larger, more complicated floor plans must generally incorporate a post-and-beam structural system, with bale infill. One big advantage of this method is the possibility of raising the roof before the bales arrive on site. This provides a ready place to store bales out of the weather, and virtually guarantees no wet bales - which has proven to be a nightmare to many a careless builder. Be sure to think through how your structure and bales will meet, as designing to minimize notching and custom bales will pay off in ease of construction. One common approach is to wrap the bale walls around the outside, leaving the posts exposed inside. This results in a tight, insulating envelope and an interior structure that is easy to tie-into. If your posts are trees left naturally round, it is all the more beautiful.

Codes

Straw-bale construction has been adopted in a number of building codes, including the state of New Mexico, and many counties in Arizona and California. This has been both a blessing and a curse for architects and builders. They have discovered that the codes they fought to have accepted are now, just a few years later, inflexible and restrictive, hindering new, improved bale-building methodologies.

Still, code approval has helped straw-bale building gain acceptance with lenders and insurance companies, paving the way for mainstream applications. And, energy efficiency is increasingly being mandated by new laws, which reflect our growing awareness of the need for conservation. In this context, straw-bale construction offers a "green" alternative to conventional housing, and, for many, a stepping-stone towards natural building and sustainability.

Trends

Despite code restrictions, experimentation continues towards simplifying bale-wall construction, reducing costs and improving performance. In a poor, but vibrant, neighborhood in Sonora, Mexico, Athena and Bill Steen have worked with local builders to develop an affordable straw-bale home with locally-available materials. Together they discovered simple solutions to working with poor-quality bales, including a technique many professionals north of the border are adopting - known as exterior pinning, or the "corset" system. Conventionally, bale builders will pin the courses of bales together by pounding overlapping rebar, bamboo, or wooden stakes down through them. They have found that it is far stronger to place a "pin" vertically on each side of the bale wall, then attach them with twine or wire pushed horizontally through the bale. This cinches the bale wall tightly together, and can firm up an otherwise shaky wall. The Steens use a local reed called Carrizo, but in other regions, any plentiful sapling would probably serve the purpose. The Steen's work with earthen and lime plasters also inspires many builders who seek a beautiful alternative to cement stucco.

In Australia, John Glassford (of Huff and Puff Constructions) has successfully built several large commercial buildings with load-bearing jumbo bales, measuring 3'x 3'x 8' (1x1x1.8m). Employing fork-lifts to place the bales and spraying them with stucco, Glassford and company constructed a factory and two wineries with this technique. These thick bales, combined with good ceiling insulation, create a large, super energy-efficient structure that can easily provide the proper environment to age a fine wine.

Retrofitting existing buildings with straw-bale insulation shows great promise in urban areas. While a quality job requires much planning and attention to detail, wrapping a sound-but-inefficient building can make a huge difference in energy bills, comfort and aesthetics. A recent retrofit by straw-bale pioneers Matts Myhrman and Judy Knox in Tucson transformed a homely block home into a work of art. In many situations, this choice to retrofit can save valuable existing resources, and reduce the energy drain of poor design.

Pushing the boundaries of strawbale, a number of builders have been experimenting with vaults, notably architects Dan Smith, Bob Theis, and Kelly Lerner. Using bamboo "exoskeletons," bales are carefully stacked and supported with falsework, until the vault is completed, then the supports are removed and the bales are plastered. The primary advantage of vaults are resource efficiency - the inexpensive bale is used for both wall and "ceiling" insulation, and provides its own structure. Thus a vault could be built nearly anywhere with a very modest cost for materials. Disadvantages include difficulties in roofing, and/or making the bales watertight, as creating a water-proof skin will also prevent water vapor from transpiring through the wall/roof area, which could cause moisture to condense in the bales. Still, Smith and Associates have secured the first permit to build a straw-bale vault, in a seismic zone of California. With continued pioneering, the straw-bale vault may yet emerge as the most cost-effective and energy-efficient bale structure possible.

A Straw-Bale Future

Given our rapidly-expanding world population and the mounting evidence of global warming, straw-bale construction is being embraced by visionaries as a solution to housing needs that minimizes the use of fossil fuels. Currently the United States has more straw-bale buildings than any other country. Rather than leading the rest of the world toward resource exhaustion, the U.S. could set an example, as more and more Americans choose to build their homes with bales - and boast about it.

Meanwhile, low-tech straw-bale methodologies are already creating affordable homes for people in far-flung communities around the globe. The Casas Que Cantan (Houses that Sing) initiative of Athena and Bill Steen in Mexico assists low-income families to construct good, decent homes for around $500 in the cost of materials. In Belarus, a government initiative has built nearly 100 straw-bale homes for families displaced by the Chernobyl nuclear accident, at one-quarter the cost of a local brick home. And in Mongolia and China, the Adventist Development Relief Agency (ADRA) introduced energy-efficient straw-bale technology into areas with extremely long, cold winters, saving 75% or more of the coal required to heat conventional buildings. A few hundred Chinese straw-bale homes may soon inspire tens of thousands, if costs can be partially subsidized by "carbon credits," for the coal not burned, and the pollution not created, in a snug, warm straw-bale house.

Builders Without Borders

Prompted by recent natural and man-made disasters, a worldwide network of natural builders has begun an initiative that seeks to share this ecological approach to building with people in need of affordable housing. Based on what is working in Mexico and China, Builders Without Borders project leaders would work with communities to assess local materials and people resources, and to develop appropriate designs for energy-efficient homes. While respecting the vernacular architecture of the region, techniques of passive solar heating and cooling, straw-bale and earthen construction, earthen and lime plasters, and low-cost, effective foundations and alternative energy systems, would be demonstrated in hands-on projects, with an emphasis on training local communities how to do it themselves. Ideally this sharing would work both ways, producing a rich human exchange, and empowering all the participants. BWB is yet a fledgling network, inspired by the excitement of natural building and a vision of a more equitable, sustainable future.

The good feelings that seem to emerge when people work together to help each other is probably the strongest magnet attracting people to straw-bale and natural building. As we work and sweat and laugh together, we remember our interdependence, and connect with those around us in an essential way. This is where building with bales is more than a methodology for a resource-efficient future, it becomes a doorway into a community that holds a hand out to those coming up behind them.

This article will appear in The Art of Natural Building: Design, Construction, Resources, due out this July from New Society Publishers. Author Catherine Wanek has traveled from Orange County to Red Square, learning about and documenting straw-bale building projects. She has produced five straw-bale videos, and spent the past three years managing and editing The Last Straw Journal. To contact her, call 505-895-5400 or email thelaststraw@strawhomes.com. Also see the websites www.strawhomes.com and www.strawbalecentral.com


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