Inspecting strawbale homes: Will this Home Dissolve When it Rains?

By Kenton Shepard 

Early last summer I was contacted by a woman suffering from Multiple Chemical Sensitivity (MCS) about inspecting a straw bale home. At the time I had a general idea of how they were built, but taking on the liability of inspecting one? Different story. I could disclaim the walls, but that wouldn't serve my client well.

In researching MCS I found that it's usually caused by an extreme exposure. My client had lived in New York and been near the World Trade Center when the towers collapsed. At times she'd had to live outside because she couldn't find a home her body could tolerate.

Mark Shueneman, Executive Director of the Colorado Strawbale Association (COSBA) lives in Boulder and I called him. "Funny your should call" Mark told me, "We're starting a three-day class in Boulder the day after tomorrow and if you want to attend, come on over". Quite the coincidence.

COSBA is interested in seeing methods developed to inspect straw bale homes so that people can feel more confident in buying them, lenders can feel more confident in loaning on them and insurers can feel more confident in insuring them. Fire insurance for a home made of straw? ARE YOU CRAZY?!! In fact, in looking for loans for these homes, successful applicants will describe them as "post and beam structures with agricultural infil" which is technically true.

I took the class and began meeting more people in the local straw bale community, which is considerable along the Colorado Front Range. There are lenders, insurers, architects, engineers, code officials, builders and plaster contractors in this part of the country familiar with this somewhat esoteric building method. I spoke with people from all these professions in gathering information from which to develop my inspection methods.

Without going too far into the nuts and bolts, straw bale homes are usually wood-framed post and beam homes which use straw bales as insulation and as a foundation for the plaster. These homes used to be plastered (inside and out) with a stucco-cement mix, but time and testing showed that earthen, lime (as in powdered limestone) or a mixture of the two provide the best plaster.

When plaster is applied directly to well-packed bale walls, the result is a very fire-resistant wall, since there's little oxygen inside the wall to fuel a fire.

Moisture is another issue, and it's important that the designer and builder know what they're doing...

• NO FLAT ROOFS
• NO PLUMBING PIPES IN THE STRAW WALLS
• KNOW HOW TO PROPERLY SEAL WALL PENETRATIONS

The list is actually much longer, but that information and more is available elsewhere .

The big fear connected with moisture in the straw is the development of decay fungus. In order to reproduce, fungus release spores. High concentrations of mold spores in indoor air can cause health problems in those with lung disease, compromised immune systems, asthma or allergies. Because there is so much food (straw) available for mold consumption, the possibilities are scary.

An advantage to straw bale homes is that the bales can absorb a lot of water before they reach the approximately 20% at which mold fungus become active. Properly designed, built and maintained the chances of bad things happening can be relatively easily managed.

STRAW BALE INSPECTION

Inspecting these homes is truly different from inspecting conventional homes. Here are some of the questions and requirements facing inspectors...

• Preliminary legwork should involve rustling up any original plans and photographs taken during construction. An inspector wants to find out what's behind the plaster.
• Where are the plumbing pipes?
• Is the first course of bales resting on the floor?
• What caused those cracks?
• How are the windows and doors flashed?
• What systems or components are likely to fail disastrously?
• What design features will route water to the straw bale walls?
• Did the plaster suffer freeze damage before it cured?

Some bad homes have been built and a bad straw bale home can be a very unhealthy home. Older homes are more likely than not to be suspect because designing to control moisture has not been well understood. In attempting to keep moisture out of the walls, many homes were more successful at sealing moisture into the walls... a bad situation when the walls are full of straw.

The high liability in inspecting these homes should be reflected in an inspector's contract language, in his inspection methods and in his price. When an inspection goes way bad, everyone can wind up in court and everyone loses, so the inspection of a straw bale home is not a place to go looking to save money.

To learn more about straw bale homes, check out my Straw Bale Home Basics article, also on the EcoBroker and NACHI websites. Please feel free to contact me with questions.