Best way to insulate crawl space in new build
Hi. I’ve asked this question before about an existing house, but now I’m building a new house and would like to make sure we get this right. Thank you to everyone who contributes here. Your insight is beyond helpful.
We are building on a barrier island in south Jersey two blocks from the beach. By code, we must have flood vents in our crawl space so it’s not possible to completely seal all air infiltration (although we are using insulated smart vents). The foundation floor has a vapor barrier and fiber glass under the rat slab. The walls are cement block, coated on the outside with waterproofing and covered with one layer of brick.
Unfortunately, we have to run the duct work for the first floor in the crawl space. The current plan is to foam the joists and bays with 3″ of closed cell spray foam and also cover the duct work with spray foam. I’m thinking that foaming the duct work might not be such a good idea after all and that maybe we should just insulate it with R8 bubble wrap.
The other alternative will be to foam the walls and condition the space as best we can. The foam installer says we can spray 3″ of closed cell foam on the walls up to and including the sill plate and rim joists. I’ve read conflicting opinions about this, though. Some say you need to leave gaps for termite inspection, others say that moisture wicking through the foundation walls has no where to go but into the wood where it will cause rot and mold so the sill shouldn’t be covered with foam (I’m pretty certain there is a vapor barrier between the block and sill). The more I read, the more confused I become.
I’m so worried that we’re going to do the wrong thing and get into a big mess. Is there anyone here that can advise me on the best way to proceed. Thanks so much!
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