Varmints and Strawbale Buildings

Catherine Wanek After growing up in Las Cruces, NM, Catherine lived in various places until she settled in Los Angeles to work as an assistant director in Hollywood film production.  Lured by the beauty of New Mexico, Catherine purchased the Black Range Lodge in the 1980s with a vision of making movies there, and developing the property into a lush permaculture landscape, which now includes an abundance of fruit trees.   Since then she has been providing a comfortable respite for others seeking rest and relaxation in a natural, healing environment.  After building a straw-bale greenhouse in 1992, she became an advocate of “natural building”, traveling internationally to research and educate, authoring books and videos, and hosting hands-on workshops at the Lodge to spread the word about ecological construction methods.  Books she has authored on these subjects include The Hybrid House: Designing with Sun Wind Water and Earth, The Art of Natural Building, and The New Strawbale Home.

Questions and Answers

Q: We have a commercial building with partial straw bail construction. The walls with the straw in them have become infested with varied carpet beetles, and some type of grain borer. Have you ever seen this problem, and if so do you have any suggestions?

A:(Owen Geiger) Insect problems in straw bale walls are quite rare if the walls are plastered correctly and kept dry. Usually, any insects in the bales are trapped and killed once the walls are plastered. So, my guess is 1. your walls have excessive moisture (have you taken any moisture readings?), 2. your walls are not adequately plastered (are there lots of cracks for moisture and insects to get through?).

Q: I've had a strawbale house built and the builder did not completely seal the straw. He has left gaps in the render on top of the walls and there are also visible cracks eg where he has butted the internal render of a straw bale wall up to an internal mud wall, so that there is a visible opening about 1/4 inch wide, from floor to ceiling. He says internal cracks and gaps don't matter as long as they are not big enough for rodents to get in and that insects don't eat straw so if they have access it is not a problem. I would very much appreciate your advice.

A:(Owen Geiger) Small "hairline" cracks are common in plaster and usually pose no problems. Larger cracks on the exterior will inevitably allow moisture to penetrate and cause problems. Larger cracks both inside and out create an entryway for insects. Maybe there isn't much food there, but with a cozy nesting site they will likely multiply and become a nuisance. Plus, cracks are very unsightly and diminish the value of your home. I suggest sealing all the cracks the best you can. One option is to buy a case of inexpensive latex painters caulk and fill the cracks. (Even unskilled workers can do this. Smear it smooth with your fingers and/or a damp rag.) Once dry, a thin touch-up coat of plaster will have your walls in perfect condition. Another option is to spray drywall texture on the walls after caulking, and then paint it. This is the standard wall finish in the US that goes on top of sheetrock. It's very fast and fairly affordable. A 1,500 square foot house could be sprayed in one day. Various textures are possible from "orange peel" to "knock-down." Ask any drywall finisher about the options. This option saves a major battle with your plasterer who may never come back. And, you'll end up with blemish free walls.

Q: Is there any chance that mice will live in the straw bale house? I know they eat it, cause it's straw.

A (Kelly): This is a common problem with straw bale houses. Often there there are grains left in the straw that would attract the rodents initially, and then once they find a way into the straw, they discover that it is warm and cozy and makes a nice home. To keep this from happening, one must be very careful to completely seal all possible entry holes with solid plaster. This is easier said than done, given the abilities of mice.

Q: What else can be done to varmint proof things. I was told lime or other caustics create a hostile environment for insects and critters find it inhospitable, true or false? Can other chemicals be used? If so what?

A:(Owen Geiger) True.  I would focus on creating a tight structure with no holes sealing the bales as quickly as possible.  This includes: Build the load-bearing structure first and get your initial inspections completed before adding bales.  Use bales freshly delivered to the site.  Install them quickly and get a coat of plaster on as soon as possible.  Leaving the bales exposed for a long time is your greatest risk.

Q: Are infestations (rodents or insects) and/or mold (from water leakage) necessarily inherent risks with strawbale homes?

A:(Owen Geiger) Well, wood can rot, burn, twist, bow, warp, attract insects, mold, etc. etc.  and yet it is very popular for building. Every building system has pros and cons.  A good designer will 'design out' potential problems so they never develop.  For example, use wide roof overhangs to keep moisture away from buildings. Also, the homeowner has to maintain the home over the years, such as patching any cracks or holes that might develop in the plaster.  This will keep insects and rodents out of the walls. Learn as much as you can about strawbale construction and you'll be fine.

Q: How do you prevent insects from penetrating through a straw bale house wall (at the floor), with a foundation of either: gravel, pallets or tires?

A: Ideally, your foundation is sealed, so that there's no air flow between inside and out, and there are no voids that become places that creepy-crawlies can live or move through. These can often be plastered to close the gaps and ultimately finish the walls. Also, diatomaceous earth, and borax (the laundry booster) can be sprinkled within the stem wall. These are relatively inexpensive and benign to humans, but deadly to many types of insects.


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