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Forums > Green Building Forums > General Forum - Residential > Subject: Underslab insulation in hot climate?

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kwalla101User is Offline
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Posts:12
08/12/2008 4:49 PM  
What about underslab insulation in climates where the cooling days outnumber the heating days? We're building a passive house in the Central Valley of California (climate zone 9b). It will be on a slab. There will be a partial basement for storage, including wine cellar/root cellar so I will leave that uninsulated underneath. But what about the 1st floor?? It seems pretty clear that a VB of 6-10 mil poly is necessary to control moisture, but arguably the heatloss in the winter won't be so bad as to outweigh the cooling capacity of an uninsulated slab in the summer. It seems that one of the following strategies would make the most sense in our situation:

- uninsulated slab with perimeter insulation to the bottom of the footer (no frost line here so that's quite shallow-- 15") and
wing insulation out to 2'.

- uninsulated slab with perimeter insulation PAST the bottom of the footer-- say to 24"-- and then wing insulation out to 2' (seems a little dodgy from a structural perspective to dig down lower than the footer to insulate to 24")

- insulated 6" slab-- would lower heat loss in the winter-- we do get SOME cold days here-- and provide a larger heat sink in the summer.

FYI, nights here in the summer are almost always cool enough to open the house and we'll have a whole house fan to bleed off the heat soaked up by the thermal mass in the slab and other areas. We'll have a couple of small areas with electric resistance radiant heating (bathroom floors, maybe 1-2 other small areas) for supplemental heat/comfort when getting out of the shower.


Any thoughts, suggestions and critical comments are most welcome.

Thanks all.
JellyUser is Offline
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Posts:274
08/13/2008 8:47 PM  
Good questions kwalla. I would add another related question, and that is whether the perimeter/sides of an elevated concrete slab (say three feet high) in a hot climate should be insulated as well.
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Forums > Green Building Forums > General Forum - Residential > Underslab insulation in hot climate?


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