Bales of straw may seem a bit simple, but they’re very effective for building a home. “Walls go up very quickly,” explains natural building expert Michael G. Smith, “because you’re working with these very large building blocks that you can just stack on top of each other.”
They’re also great insulation, offering R2 per inch thickness of the wall. Smith and his team are using 16 inch wide bales for the walls of the community center they’re building on the premises of Mendocino County’s (California) Emerald Earth Sanctuary. Add another couple inches on both sides once its been plastered and you end up with about a 20 inch wall and impressive insulating value.
And according to the California Rice Commission, building with straw bales can be cheaper (these are numbers from the mid-nineties). “Owner-builders who elect to do most of their own work and minimize the incorporation of other building materials in their design will spend approximately $30 per square foot, in comparison to conventional wood-frame construction, which typically costs about $75 per square foot”.
For those worried about the flamability of straw, once the plaster goes up, it’s incredibly strong. According to testing by the National Research Council of Canada, a plastered straw bale surface can withstand 1850°F for 2 hours before cracking.
The only downside with straw bale is that its difficult to use for framing windows and doors. So in an area with a lot of openings, Smith suggests switching to something like light straw clay (aka slip straw).
In this video, Smith shows us a portion of the wall with exposed bales, a portion with a first layer of earthen plaster and their system for pinning and attaching the bales together using wooden 1-by-2s.
[Note: To get an idea of how much straw bale you’d need to build a home, here is an estimate from the California Rice Commission. “A 1,600- square-foot house requires approximately 500 bales. At 80 pounds per bale, this corresponds to about 20 tons, or the rice straw from 6 acres.”]