Straw bale building is a superior way to build. It is the most resource-efficient way to build a superinsulated energy-efficient building. Insulation is the key to energy efficient buildings because it makes the most of the energy used to heat or cool the building. Insulation is measured in R-value, which rates a material’s resistance to heat flow (the higher the number, the higher the resistance). A well-built 2”x6” wood-framed wall is R19, a straw bale wall is between R30 and R40.
Less energy goes into building a straw bale building and less energy is require to run it. Straw bale buildings are two to three times more resistant to heat flow than conventional buildings. Other forms of superinsulation exist but require large amounts of high-embodied energy materials such (as foam or fiberglass) to achieve the same result. The embodied energy of straw is 1/100th that of fiberglass insulation.
Straw is an annually renewed agricultural waste product: it is the by-product of the production of grain. Except for the energy used to bale the straw, all the energy used to create a straw bale was necessary for the production of food. Though there are some other uses for straw (animal bedding and erosion control) much more straw is produced than is needed. Until recently, farmers would burn the straw in the fields which produced significant air pollution.
Because plastered bales have little oxygen available for fire, straw bale buildings have a better fire-resistance rating than most conventional buildings (1 hr for clay-plastered, 2 hrs for lime-cement plastered). Plastered straw bales replace the insulation, drywall, paint, and some of the wood used in a conventional system. The plasters can be created with very low-embodied energy materials such as local clay soil mixed with leftover straw.
Clay plastered straw bale walls deal with indoor moisture well, storing excess moisture when it is damp and then releasing it when the air becomes drier. Plastered straw bale walls provide good sound insulation and have been able to withstand winds in excess of 130 miles per hour. Anecdotal evidence from Israel tells us that straw bale walls can stop bullets from an AK47.
Interested in hearing more? We are available to present talks, lectures, and demonstrations to your school, church, or other group. Content can be tailored to your groups’ interest. Contact us for more information.
Watch our video about the basics of stacking bales.
Want the raw data? Here’s a link to the testing that has been done by the Ecological Building Network: straw bale test results, including structural, moisture, and fire resistance tests.
But won’t it burn? Won’t bugs eat it? Won’t the it get blown down by a wolf? Read the FAQ’s about straw bale building from the California Straw Building Association http://strawbuilding.org/sb/faq.html