Straw-bale homes are providing low-cost housing for do-it-yourselfers throughout the U.S., Canada, and Australia. Never before has such an unconventional building system gained acceptance so quickly. Properly designed straw-bale homes, usually composed of wheat or rice straw and coated with plaster and stucco, are resistant to moisture, fire, and pests.
The walls of straw bale homes are between 14 and 23 inches thick, depending on the size of the bales and how they are laid within the wall. The estimated thermal resistance or R-value of straw bale walls is between R-25 and R-50. The actual R-value may vary considerably between straw bale walls, depending on how much air convection occurs within bales and heat traveling from indoors to outdoors along the surface of the stucco, which coats the bales.
One disadvantage of straw bale construction is that your local trades people may be unfamiliar with how to build, wire, and plumb these unusual walls. Your code officials may also be at a loss as to how to evaluate your plans. The straw-bale system is slowing gaining acceptance, though, and the city of Tucson, Arizona recently developed building-code modifications for straw-bale homes. Similar code changes have also been recommended to local governments in California by the State legislature.
The Canada Mortgage and Housing Corporation (CHMC) studied 17 straw bale homes and used computer simulations to compare straw bale homes to conventional homes with the same physical characteristics (floor area, compass orientation, and window area). CMHC concluded that the straw bale homes studied use 20 percent less energy for heating than standard homes with standard two-by-six insulated walls.
Since straw bale homes are still uncommon, they work best for the skilled do-it-yourselfer with a limited budget and lots of time and energy to dedicate to their building project. But they can be a good option for homeowners who want an energy efficient home using natural materials.
See Foam Wall Insulation Systems for New Homes and New-Home Wall Insulation for Your New Home for more conventional ways to achieve a high wall R-value.