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Hi, new member here. I am renovating a 25’x20’ guesthouse in a wooded area next to a pond in Wisconsin. So it is a damp climate that ranges maybe from -20 to 110 degrees at the extremes. The floor of the cabin is 10” joists over a 2’ crawl space of dirt. I encapsulated the crawl space the best I could with a heavy plastic vapor barrier, then layed pressure treated plywood across the bottom of the joists to act as a support for foam and had 4” of closed-cell foam sprayed between the joists. My plan was to lay 1/2” pex on top of the spray foam between the joists, then put the subfloor down. My knee jerk thought was to put a reflective foil down between the foam and the pex, but I started to think that there could be risk of condensation between the foil and foam if there is a significant heat gradient. A friend also mentioned the thought of pouring concrete in to act as thermal mass, but that might be a separate question. Thoughts? Thanks people!
 

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retired framer
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For condensation you would need a constant supply of warm moist air to come into contact with a cold or cooler surface.
So, which will be the cold surface and where will the air be supplied from.
I would be worried about nailing down a hard wood floor with pex right below.
A friend had a similar system in a house with the pex just attached to the joists a little lower with fiberglass insulation and it seemed to work fine. With out reflective anything.
They glued down the hardwood.
 

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The radiant barrier below the pex would be needed if there was a significant amount of heat loss going down. With 4" of closed cell foam I don't see a lot of heat loss into that crawlspace.

Not sure about your approach of encapsulating the crawl and then isolating it from the conditioned space above. I like to see encapsulated spaces insulated and conditioned.

Will this house be conditioned year round of just occasionally?

Bud
 
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