Flashing and exterior basement insulation detail
I am about to break ground on a basement foundation for an existing cabin that will be moved on top of it and am running into some last minute design problems. My intention was to insulate the interior walls with 2″ rigid foam and then build a 2×4 wall in front. Because of the way the existing cabin is built (the bottom of the 2×6 floor joists are higher than the bottom of the log), the 2×4 wall has to be load bearing and continue down to sit over the footer. The footer wasn’t designed wide enough for the wall to sit on it if I space the 2×4 wall 2″ from the concrete for foam. I’m supposed to start excavation mid next week. Options i’m considering:
1. build a ledger into the concrete wall and sit the 2×6 on that, continue with planned interior foam plan.
2. foam exterior walls instead. Plan is to have 9′ walls, 5′ below, 4′ above grade. In this case the foam would sit proud of the log walls and I would have to flash the top foam edge and side the foam. This solution seems like potentially the best except I can’t figure out flashing details since i have log. I could put on the exterior foam, then L-flash, then place the cabin on top perhaps? Once the cabin is placed it seems like my options for flashing get more complicated – like somehow getting a kerf cut and sliding z flashing with caulk into it? If anyone has a better idea i’d appreciate it.
3. Another interior insulation method i’m not thinking of? I’m in zone 6b, so I am pretty dry and my area is known for rocky, well draining soil. From my research on this site it seems the safest way to assure no moisture issues is to only use either rigid foam on the interior or exterior, or spray in with a gap between the 2×4 wall and concrete. Is there another way I can safely insulate with the 2×4 right up against the concrete if i don’t do exterior insulation? Thanks!
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