Crawlspace insulation advice
An acquaintance got an estimate to insulate her 16’x18′ crawlspace. Although I haven’t seen it personally, here’s the scenario:
House is in WI, 7600 degree days, concrete block foundation (no vents to outside) with bare soil in crawlspace. However, the soil is dug down quite a bit deeper next to the foundation, so the soil slopes up towards the center of the crawlspace (about 2.5 ft. high in the middle). Forced air ducts run through the crawlspace, and the access to the crawlspace is a former basement window, which is open to the basement.
Contractor is proposing putting 8 mil poly on the soil, and sealing it to the foundation (not sure how high up they plan to lap the poly). Then they would spray foam from sill box all the way down to the soil.
The owner asked about insulating the soil as well, so contractor gave the option of NOT using poly and putting down 2″ Thermax (only after owner paid someone else to level out the soil), taping the seams. The reason he gave for no poly was the possibility of condensation on the foil on the bottom side of the Thermax. Extra charge for the Thermax option is $1000. The reason for using 2″ Thermax is the owner was concerned about the rigid foam cracking if anyone ever had to crawl across it.
The contractor is skeptical of the benefit of doing the Thermax option (as am I), but I said I’d ask for advice via this forum.
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