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Old 06-07-2012, 09:56 AM   #1
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XPS on floor sealing questions


So, I've been reading a lot and I think I'm going to finish my basement floor like so:

The existing floor is 4 inch of concrete over 4 inch clean stone with perf pipe to gravity fed sump. I've never had floor moisture issues, but I also know there is no vapor barrier under the concrete.

I think I'm going to use 1/2 inch XPS under 2 layers of 1/2 inch ply (alternating directions)

I will use tyvek tape to seal the joints in the XPS (using 2 inch XPS on block walls as well)

My question is about the foam sealant. Say on the flooring where the XPS butts (or overlaps...haven't bought the stuff yet), if tight and taped, do i need to spray foam, too? If so, would I use Great Stuff or..? And where would that go. On the concrete where the pieces meet or on the top where the tape goes?




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Old 06-08-2012, 07:44 AM   #2
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Why 2 layers of plywood? XPS has very good compressive strength and should be fine under a plywood deck. Might as well have 1" of foam on the floor instead of 1/2"

Use foam to seal the larger gaps (closed cell) and sealant and tap to seal all the seams.


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Old 06-12-2012, 11:31 PM   #3
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I'd go with two layers as you said, that much better at stopping room air getting to the slab; http://www.buildingscience.com/docum...g-your-basment

The thicker foam board is recommended for colder climates; http://www.buildingfoundation.umn.ed...timum-main.htm

where are you located?

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Old 06-13-2012, 06:58 AM   #4
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I'm in NJ. It gets (relatively) cold in the winter...can get down in the teens, at any rate. And, of course, up to 100 in the summer.

I grew up in AK, so I know it doesn't get THAT cold. ;-)
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