Remodel – Insulating a permanent wood foundation (PWF)
We recently purchased a log home built on top of a Permanent Wood Foundation (PWF). It’s a ranch style (26’x47′) single story. Built in 1980. We have completely gutted the basement. We are down to the 2×6 stud walls 1-foot on center of the PWF. Previously the house was heated via a wood burning furnace and electric baseboard heat, which have both been removed. We had geo-thermal installed utilizing the duct-work that was in place for the wood burning furnace. It’s a ground source heat pump made by Water Furnace (5 Series).
When we gutted the basement, the walls had wood paneling on top of the sheetrock. The sheetrock was not taped or mudded. Behind the sheetrock was a vapor barrier that was stapled to the studs and the stud cavities had unfaced batt insulation. When removing the batt insulation we could feel it was a little damp near the bottom in a few spots. The batt insulation filled the cavity and there was no gap behind it, or at the bottom. The batt insulation was in contact with the concrete because the concrete was poured over the bottom plate. There wasn’t any mold. The basement did have a very slight damp/musty smell to it. The carpet and pad was installed directly on the concrete which may have been the culprit for the damp smell.
The only time I’ve seen water in the basement was when we had a heavy rainstorm come through in the early spring and the frost had not let up out of the ground yet. Water was coming in through the wood sheeting on the PWF in a few spots and pooling in the bottom of the stud cavities. Which reminds me, the soil where the house is built is all sand. When they dug the 300′ trench for the geo, it was all sand. That trench was 8′ deep, and 8′ wide.
We are in climate zone 6A, Eau Claire, WI area. Onto my question…
We were considering spray foam insulation but it is extremely expensive and we are concerned about the breath-ability of the walls. I have ordered and gone through Joe Lstiburek’s book, “Builder’s Guide to Cold Climates” where he states that the wood wall is warm and will dry to the interior. The book shows how to assemble a wall on new construction and has the rigid insulation on the exterior. I like the idea of the rigid insulation on the exterior… but I’m curious if I would have to install it ALL the down to the footing, or if it could be installed from the top plate to 16-18″ below grade? Then on top of that… how could I make the transition from the logs to the rigid insulation as the rigid insulation will now be sticking out three inches? As I stated in the beginning, it’s a log home, with full logs. So, I can’t carry the rigid insulation all the way up to the roof line. Also, how would you retrofit the rigid insulation around existing penetrations (water faucets, electrical service coming in, windows, etc)?
OR… do I just follow the 2015 American Wood Council (AWC) guidelines for PWF and insulating on page 15? http://www.awc.org/pdf/codes-standards/publications/pwf/AWC-PWF2015-Commentary-ViewOnly-1411.pdf As I type this out and think about it, I’m leaning towards the AWC guidelines because super sealing and insulating the basement isn’t going to “make-up” for the insulating values of the logs. Also, the previous batt insulation was there for 36 years and there wasn’t mold… so, it works. If I go this route, I will just have to spend some time insulating the rim joists with rigid insulation and Great Stuff spray foam..
Looking for some guidance / advice. I’m not afraid of digging in and doing the work. I just only want to do the work once. There will be two bedrooms down there for my kids. I want them to be comfortable.