Answer: Without adequate safeguards, rot can occur. The most important safeguard is to buy dry bales and keep them dry until safely sealed into the walls. If used, paint for interior and interior wall surfaces should be permeable to water vapor so that moisture doesn't get trapped inside the walls. Design and construction must prevent water from gathering where the first course of bales meets the foundation, and at the top of the bales (along with a fire stop.) Even if straw bales are coated, the foundation upon which the bales rest should be elevated above outside ground level by at least six inches or more. This protects the bales from rain water splashing off the roof and snow piled at the foundation. Roof overhangs and eaves should extend two to three feet beyond the walls. Porches and verandahs offer good protection, as well.
Question: Will pests destroy the walls?
Answer: Straw bales provide fewer havens for pests such as insects and vermin than conventional wood framing. Once plastered, good maintenance practices keep any cracks and holes sealed, so any chance of access is eliminated. There is virtually no nutritional value in straw. Nothing will eat it except fungi (and then only if it gets very wet). A mouse might tunnel into a straw-bale wall if it is not protected by stucco or plaster, but mice could just as easily take up residence in your wood-framed house if you allowed a hole through the exterior. Proper sealing of the wall surface (top, bottom, sides) is required to keep a straw-bale building or any other type of building pest free.
Question: Are straw-bale buildings a fire hazard?
Answer: Testing of plastered straw-bale walls for fire safety found them to perform better than conventional building materials. In fact, the plaster surface of one certified test withstood temperatures of about 1,850 degrees Fahrenheit for two hours before any cracks developed.
Question: Are straw-bale buildings acceptable to local building codes?
Answer: City, county, and state building codes may vary. Some building sites may not require codes. Some states, counties or cities may have codes that incorporate straw-bale construction. In most cases, infill is generally acceptable but may require an engineer's stamp; load-bearing straw-bale walls must be engineer certified. Check with your local codes official early in your project planning and project design. Always follow electrical, plumbing, fire and other local code provisions.
Through her consulting business, ReBuild Associates, Joyce Coppinger helps develop building projects using strawbale and natural building methods and materials. She teaches strawbale and natural building through classroom seminars and hands-on workshops in the Great Plains region. She is managing editor and publisher of The Last Straw, a 40-page international journal on strawbale and natural building. She is co-coordinator of the Lincoln Green Building Group.