Crawlspace Rim Joist Insulation
Climate zone 3C (95062, coastal California).
My primary concern is not rotting out my rim joist.
I’ve been slowly retrofitting my single-level home’s crawlspace. Starting with a traditionally vented crawlspace, I’ve added a vapor barrier on the ground, extending up 3-4″ on the concrete stem wall. Vents have been closed and a dehumidifier is used in the summer. A radon fan also runs which currently vents the entire crawlspace at a very low CFM which someday will be ported correctly below the vapor barrier.
On the exterior of the home, the stucco runs all the way down the wall and is buried in the dirt. I’ve been cutting this back so it is no longer in contact with the ground but haven’t finished the entire home yet. I can get at least 1.5″ of air space between the stucco and the dirt in most places (although some directly touches a patio slab and garage slab). I’d like more than 1.5″ but this is already after some significant (to me) earth moving to achieve this. No weep screed but I figure it’s better than being buried.
I am now insulating the rim joist with 2″ of polyiso and spray-foaming it into place.
There is no water control layer on the exterior of stem wall. I also do not believe there is any separation between the stem wall and wood sill plate.
Humidity levels in the crawlspace hover 40-50% RH in winter and are maintained at 60% in the summer.
How worried should I be about rotting out my rim joist? My main fear is the stem wall slurping up moisture and transferring it to the wood.
A picture and detail are attached.
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