Building with straw bales began on the Great Plains in the 1880s when pioneering farmers realized they could create straw building blocks with newly invented baling machines. Surrounded by grasslands and wheat fields and very few trees, they developed what became known as a “Nebraska” style load bearing straw bale building. The straw bale walls supported roof loads, and scarce wood was used only in doors, window frames, and for the roof. Many of those buildings are still standing today. A straw bale building revival started almost 100 years later, led by modern day pioneers in sustainable building. Folks like Matts Myhrman and Judy Knox, Bill and Athena Steen, and David Eisenberg revived this uniquely American building system and moved it forward. Today, there are straw bale buildings throughout the world, and straw bale building is in the International Residential Code, IRC Appendix S: Strawbale Construction, adopted in Oregon, California, and other states. Non-load bearing straw bale wall systems have evolved. Along the seismically active West Coast, most straw bale structures have posts-and-beams or timber frames to support roofs and resist shear loads, and use plastered straw bales as insulation and thermal mass infill.
Straw bale building owes its growing popularity to several important factors:
- Straw is an annually renewable agricultural “waste” product; the woody stems left over from the harvest of wheat, rice, barley, or oats—crops grown throughout the world. No one complains when a farmer “clear cuts” a wheat field.
- 18” and 24” thick straw bale walls have an R-Value of between R-28 and R-34, and because they are plastered on both sides, combine insulation with thermal mass for an incredibly stable wall that buffers temperature swings, requiring smaller heating systems, and perhaps no cooling system at all.
- Straw sequesters sixty times more carbon than is required to grow it, giving it the lowest carbon footprint of any insulation material today.
- Straw is a natural material. While a small amount of petroleum based fertilizers and herbicides are used to grow the crops, this tiny amount pales when compared to the pollution and greenhouse gases created by manufactured insulations like fiberglass, closed cell spray polyurethane, and extruded polystyrene. Cotton and blown-in-cellulose insulations are both natural too, and both made from recycled materials, but cotton is a water, herbicide, and pesticide intensive crop, and cellulose comes from trees, which have a much longer growing cycle.
- Straw bale structures are beautiful, offering unique features like deep window recesses that serve as seats or shelves, and soft, gently curving walls that reflect light quite differently machined flat surfaces.
Straw can play an important role in helping America create a sustainable path forward. Enough straw is grown in the United States that if we used only one-half of it for building, we could still build ten million 2,000 square foot homes each year! For comparison, there were fewer than one million new home starts in 2016. By using this simple, sustainable, non-toxic, time-tested building material, we could begin to replace dilapidated housing stock with energy efficient, beautiful homes, made from annually renewable, locally grown building materials.
Are there trade-offs? Yes. As Matts Myhrman has said, “you can do anything with straw-bales, except have skinny walls!” Most plastered straw bale walls are between 18” and 26" thick—compared to conventional stud framed walls that range from 4” to 6” thick, or newer “green” buildings that have double stud walls or other materials that range from 8” to 12” thick. A straw bale wall assembly offers superior insulation and distributed thermal mass, but at the price of thicker walls. The implication for a 30’ x 60’, 1,800 square foot straw bale home (exterior measurement) with twenty-four inch thick walls is that the occupant has 1,568 square feet of living space, not including window seats and window stools. Eighteen inch thick straw bale walls yield 1,596 square feet with only a slight insulation loss. A comparably sized “green” building with a 12” thick wall would offer 1,624 square feet of living space. Thoughtful design can alleviate some of this constraint—pocket doors, efficient kitchens and utility rooms, clever storage solutions, incorporating window seats into dining and living areas, etc.
Also, foundations for straw bale homes can be slab-on-grade, or the walls can rest on a floor supported by stem walls, but because the straw bale walls are wider they often require a wider footing—which usually means more concrete. Finally, straw bale walls must be covered with a plaster on both sides. Those plasters might be made from a clay, lime, or lime-cement binder combined with sand, and sometimes with chopped straw. Sometimes the clay plaster can be made from clay-rich site soils, which will have a lower embodied energy cost than manufactured materials. Because the plasters range from 1" to 2" thick they’ll contribute more to the wall system’s thermal mass than a layer of sheet rock. However, plastering usually requires more labor than sheet rock or siding. Electricity and plumbing runs are handled a little differently from conventional construction, which might take more time if installed by an electrician or plumber unfamiliar with straw bale wall systems.
Other than that, straw bale homes are just like most other homes—they have roofs and floors, doors and windows, kitchens, bathrooms, and bedrooms.
Is a straw bale wall suitable for all building designs? No. Like any cellulose based materials (wood, cellulous insulation), straw must be kept dry. Plastered straw walls need good protection from wet weather, which usually means adequate roof overhangs to shelter the walls from rain. Tall walls and tiny roof overhangs invite trouble to any cellulose building material, including straw. Straw walls cannot be used below grade. Also, straw bales structures make more sense the closer they are to regions that grow rice, wheat, oat, and barley crops because long-distance transportation costs can be high. Thankfully, the western United States has abundant grain crops. Wheat and rice straw bales from Northern California and barley straw bales from Southern Oregon are readily available in the Rogue Valley.
The Rogue and Applegate Valleys are blessed with a Mediterranean climate—comfortable enough to be outside much of the year—and relatively short, mild winters. This is a good match for people who want to live in a not-too-big house surrounded with patios and porches where they can enjoy being outdoors much of the time. Why not make it a beautiful, hand crafted straw bale home, made mostly from sustainably harvested, locally abundant building materials, heated by the sun and a small, energy efficient system, and cooled by nothing more than the night air flowing through open windows?
