Open vs Closed Cell on Rim / Band Joist
– Climate zone 4
– Brick sided home, with air vented air gap behind (1″ typ)
– Home is over an encapsulated crawlspace.
– Crawlspace floor sealed is with poly vapor barrier, the block walls are covered with R12 of closed cell foam.
– The HVAC system is in the crawlspace and “conditions” the space as required (two ports direct conditioned air into the crawlspace).
– The crawlspace also contains a heat pump water heater
The rim has r19 batts and I want to improve that so I get air sealing along with the insulation. The two easiest approaches, AFAIK, are to use spray foam either open or closed.
open cell would allow for inward drying potential of the band joist and mud sill, but since its open there is potential for moister air to condense on the band during the winter months.
closed cell prevents inward drying but would also prevent winter condensation. But it then needs to depend solely on outward drying and here is the brick, / mortar droppings and potential for the home owner to put a flower bed where it does not belong, etc.
So I’m looking for what others have done for this set of conditions. My current thinking is the open cell mainly due to the “conditioned” space it faces should have a low RH.
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