Straw Bale Construction

Environmental Mission > LEED Gold Welcoming Center > Eco-Friendly Construction

We used over 1000 straw bales for the exterior walls of our Welcome Center. They are exactly the same type of bales that you would see around Halloween—they measure 25” x 15” x 48”. The straw bales at the Presentation Center were installed by two Tibetan men—a Buddhist monk and a layman—who spoke no English and lived in a trailer by the pond for 3 to 4 months in late 2004. They placed the straw bales by hand, cutting and shaping them with machete-like tools and filling in the gaps with loose straw, creating thick, highly compacted walls of straw.

Why straw?

Straw is both a rapidly renewable resource and an abundant agricultural waste product. It requires little energy to bale and transfer for construction, and in many cases would simply be discarded if an appropriate use for it was not found. Our straw originated from Davis, CA, which is only about 120 miles away, making it a local resource as well.

From a practical standpoint, the straw bale walls, when finished with plaster, provide excellent thermal mass. Thermal mass is a part of the over all passive solar design of the building and is discussed in more detail there. Straw bale is also an excellent insulator, with an insulation rating of R-30. This in turn eliminates the need for fiberglass insulation, which among other things has formaldehyde in it, and the need for plywood in the walls, which can contain nasty glues that outgas over time.

A final benefit of straw bale construction is that it provides outstanding fire and seismic protection! It does not seem to make sense that building with straw bale would increase the fire safety of a building, as straw is so obviously flammable. However, fire needs ample temperature, fuel and oxygen. By compressing the straw into bales, the amount of oxygen is greatly reduced. After the surface of a straw bale or bale wall has been charred, the worse it can generally do is smolder, making it actually significantly safer than a typical wood stud with air space construction. Also, adding plaster to the outside, which is itself fire resistant, only increases the fire safety of straw bale construction. As for seismic protection, the straw bale walls have impressive ductile and compressive structural strength, which dampens the shock waves experienced during an earthquake.