Insulating and Air Sealing Rim Joist / No Sill Plate
I have a (fairly) newly built house (build around 2000) and am looking to do some efficiency improvements starting with the basement – had a few questions to make sure I don’t introduce any problems. We are in the Atlantic Canada (Zone 6)
For some reason the house doesn’t appear to have a sill plate/gasket installed – the house uses OSB I-joists that are resting directly on the foundation. See:
I can’t see any kind of capillary break there at all unless it’s really tiny
The house does not appear to have symptoms of sagging joists around perimeter, uneven floor etc., and foundation is 2-3 feet above the soil-level so I can only presume that moisture wicking into the floor joists/rim joists has not been a major issue – I spot-checked several places where accessible and did not observe any softness in the I-joist contact points.
In the spots where the rim joist makes contact I don’t observe any gaps whatsoever, however part of the basement is finished so I can’t do a thorough check.
So, my questions are:
1) Is it worth it to air-seal (spray foam) the edges of the rim joist given that there are no obvious gaps in the areas that I can see/access?
2) If I do this air sealing, will it significantly inhibit any of the natural drying that the house has enjoyed in its 20 year existence and introduce any problems?
3) When I go one step further and insulate the basement walls, thereby making foundation wall colder overall (presumably at the top even if it’s exposed) will it create condensation issues up there and expose the joists to moisture?
Note that in the area between floor joists and rim-joists, there are fibreglass batts shoved in there at the moment but no air sealing.
I will also note that the OSB sheathing around the house seems to overlap and is flush with the foundation walls in most of the areas I checked. Whether this is good or bad, I guess that it also provides a bit more air-tightness
Any insight or alternative recommendations? I could perhaps seal off the joist bays entirely to prevent condensation but my worry would be that any moisture making its way to the joists due to capillary action would have trouble dissipating (even accounting for using something slightly vapour permeable and I suppose accounting for the fact that it is vapour permeable to the exterior there would be a lot less airflow)
Thanks for any help!
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