Straw-bale construction

Straw-bale construction was pioneered in Nebraska in the early 20th century, in response to the lack of significant amounts of lumber with which to build housing. Often, the straw bale house was seen as a make-shift structure, to provide temporary lodging until enough funds were available for a "real" house. However, the houses were much more comfortable than their conventional counterparts and soon became regarded as permanent housing.

Straw-bale construction experienced a re-emergence in the late 1970s, when the energy crisis caused many people to rethink their approach to building construction, with an eye towards sustainability. It continues to be an attractive, sustainable method of construction.

The increased thermal comfort of a straw bale house is achieved due to the exceptional insulative value of straw. The theoretical R value (thermal resistivity) for a 16.5" straw bale was calculated by Joseph McCabe as 52. This is compared with a theoretical R value for 3.5" of fiberglass (the conventional insulation material used in home construction) of 13.

Opponents of straw-bale construction point to lab tests of straw-bale assemblies in which the R value was significantly lower. The most conservative of these results still suggests an R-value of 30, which is a significant improvement over building code requirements. Straw-bale experts suggest that it is possible to approach theoretical R values by giving more attention to detailing.

Construction of straw bale walls is achieved by stacking bales in a running bond, securing them to a top-plate assembly, and stuccoing interior and exterior surfaces. The traditional approach of using a vapor barrier is not recommended, due to the ability of excessive moisture build-up to degrade straw. During construction, various methods of pinning for dimensional stability are used. Structural analysis has shown that the straw-bale/stucco assembly behaves much like a sandwich panel, with the stucco skins bearing the load and adding considerable strength to the wall.

The cost of building with straw bales has historically been slightly higher than conventional construction (built only to code). This extra cost is incurred due to labor-intensive plaster/stucco work. However, when compared to other super-insulated construction, straw bale construction is usually much cheaper.

For more construction and historical information, "The Straw Bale House" by Bill and Athena Steen is a great book. More of their work can be seen at: www.caneloproject.com