An unusual wall system whose popularity has spread rapidly in recent years is straw bale construction. In this system, bales of straw that are a by-product from cereal grain production provide an insulative infill or insulation plus the actual structural component of walls. In load-bearing bale construction, bales stacked in a running bond support the weight of the roof and furnish the structural wall. Non-load-bearing construction, by contrast, uses bales as an infill or curtain wall in conjunction with a structural framework of wood, metal, or other materials.
Although straw has a relatively low R-value per inch, the thick bales produce approximately an R-36 wall. Straw bale walls are often finished with stucco on the exterior and plaster inside, although common finishes such as wood-based siding and gypsum drywall have also been used, especially on non-load-bearing designs.
Straw bale construction has been used for residential, commercial and institutional buildings across the United States and in Canada.
Straw bale construction is often perceived as a low-cost construction technology, because the bales themselves are inexpensive, and can be stacked into a wall by unskilled laborers. Homeowners often want to provide "sweat equity" in straw bale construction projects to reduce costs. Many people have assembled straw bale buildings during work parties or workshops. It is helpful to remember, though, that many of the costs of an alternative building system may stem from connecting it with conventional foundations, roofs, doors, windows, mechanical and electrical systems. Also, stucco and plaster finishes can be more expensive than other standard finishes commonly used today. Although many tasks can be achieved by enthusiastic owner/builders, it may be a challenge to balance the financial cost of an alternative construction system with a tight construction schedule.
Bottom line:
Straw bale construction can be resource efficient because it uses an annually renewable resource as the primary construction material. Often straw can be obtained from a Local Source, increasing the resource efficiency of this technology. Be aware that thick straw walls may not result in reduced material use, because the livable space is smaller than the building footprint. Consequently, straw bale construction technology may be less appropriate for urban sites and small or narrow lots.
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