Pesticide treated rigid foam
I am fairly close to a Cellofoam plant (www.cellofoam.com) and can buy 25 pound, one inch rigid XPS for my slab edge insulation that has been treated with Preventol insecticide. I’m not wild about using insecticides anywhere, but this seems to be one of those situations where it is worth the risk. Zone 3 is a pretty tough area for termites and carpenter ants, and I’d like to keep them away from my framing.
I have also received differing opinions on how much sub-slab insulation to use. There seems to be consensus on treating the edge (a four inch band), but that’s where unanimity ends. It’s been suggested that I include zero, two feet, and foot feet of insulation extending back from the edge.
I’m building to Earthcraft Plantinum. But Earthcraft has very limited requirements for sub-slab insulation in Zone 3 homes.
Thanks in advance for helping me to better understand how to build an efficient house. 🙂
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Steven,
In your climate, it may be hard to justify the cost of a continuous layer of rigid foam insulation under your slab (something that should always be installed farther north). The decision is complicated by the fact that keeping a slab in contact with the earth can be advantageous during the cooling season.
Perhaps other Climate Zone 3 readers will offer their advice.
Thanks, Martin.
I contacted a local green architect, and he agreed with your assessment. But to be on the safe side, he recommended no less than two feet of insulation under the slab. Better safe than sorry seemed to be his bottom line, and that's hard to argue with.