Rim joist insulation: no sill plate
Hi everyone!
First time poster, long-time lurker. This site has been incredible as I slowly DIY my new to me home. I am currently working on insulating my rim joists. Zone 6, house was built in 1992 with only fiberglass batts in the rim joists. Dry basement with dehumidifier running in the summers. Rim joists look to be in great shape overall with some very very slight discoloring in areas from previous dampness. Rim joists are above grade.
My concern is that there is not a sill plate: the rim joist and my floor joists are sitting directly on the concrete foundation. There is no capillary break for the floor joist or rim joist. (just a tiny bit of what appears to be fiberglass insulation under each floor joist).
I have been adding 2″ EPS rigid foam with great stuff pro around it, and then R-13 Mineral Wool batts. Should I be concerned about the floor and rim joists contact with the concrete, and if doing the rigid foam sealing will effect drying ability (i.e. increase chance of rim/floor joist rot?). Obviously I am doing this update for energy efficiency, comfort, and cost savings. However, if this would put my floor joists at risk and risk massive costs down the road obviously I would reserve course.
The caulking in the pictures was just added by me, there had no caulk/sealing since it was built outside of the fiberglass batts.
Thank you so much!
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Replies
TSD,
The problem is we don't know. How much the joists were relying on the heat from the interior to dry, and how much moisture is making its way up the wall to the joists is very dependent on both climate, and the conditions in your particular house. Most houses like yours are fine when the rim-joists air-sealed and insulated. Some aren't.
What would you do in this situation? Just foam? Just mineral wool?
TSD,
Depends on how much work you want to put in.
The safest would be to work your way around the perimeter jacking up the joists just sufficiently to slide a piece of 1/6” plastic stock. You could then insulate and air-seal with foam board.
Just air-sealing will bring big benefits, and should still leave the joists warm enough to avoid moisture accumulation.
Adding insulation is where the risk increases. Maybe do a smallish section and see how it does over a full year?