Insulating old stone foundation rim joist area
Stankbot
| Posted in General Questions on
Good evening!
I was curious how to insulate the space between the rim joist and the next joist sitting on the old cut stone foundation. The house was built in 1920’s and there is no sill gasket under any of the wood bracing sitting on the stone. What can I put in there that won’t be an issue for moisture. The access is incredibly limited, as in .5″. The space is 22′ x 10″ x 15″. I don’t necessarily want to cut the joist or the stone for access but not opposed to it. The outside is under a covered porch. I am in climate zone 5 bordering climate zone 4
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Replies
Wood on stone is considered safe from moisture so long as it's above the ground. For the most part stone doesn't wick moisture the way concrete does.
If the exterior face of your rim joist is able to dry (not covered with vapor impermeable insulation or other vapor barrier), then you're in better shape overall, and the interior side inulation is less critical. I like to use cut pieces of EPS held in place with canned foam when I want to leave a little drying ability for interior side rim joist insulation, but if you have really restricted access, spray foam might be your only practical option here.
Bill
Thank you both for the info. I was really worried that moisture would be a much bigger issue. I'll probably be going with the spray foam route due to space restrictions. I wanted to add a picture but the file size was too large on my phone). I'll be excited to get rid of the draft that keeps a permeant chill on my feet as the temperature drops.
Moisture wicking is more of an issue with concrete or block, cut stone tends to be much less of a problem. The mortar joints between stones may be an issue if you have wet ground near the home, so I would check that to be safe. If you have the ends of joists embedded in the foundation walls, I'd be careful there too.
The downside to sealing the rim joist is that if moisture gets in from the exterior, or through the foundation walls, there is much less drying potential for the wood, which increases the risk of rot. Since you have lest risk of moisture wicking with the stone, I would not be too worried unless the top of the foundation wall is at or near grade, or if you've had bulk water issues in the past.
Bill