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Is it necessary to tape joints in under-slab insulation?

I'm putting recycled 4" XPS under my slab. Zone 6. Do the joints need to be sealed with anything? I'll put poly on top, under the concrete.

Asked by stephen sheehy
Posted Aug 11, 2014 8:08 PM ET
Edited Aug 18, 2014 4:57 AM ET


5 Answers

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Nope- the taping would have negligible value at best. The amount of thermal bypass air movement under the slab is miniscule, and the poly layer makes it air & water-vapor tight.

Answered by Dana Dorsett
Posted Aug 12, 2014 10:10 AM ET


Thanks, Dana-That's what I hoped was the case. Your explanation makes sense.

Answered by stephen sheehy
Posted Aug 12, 2014 10:19 AM ET


You doing one layer of 4" or 2 layers of 2"? Good to have staggered seams.

Answered by Dan Kolbert
Posted Aug 12, 2014 7:42 PM ET


Dan-we're using 4".

Answered by stephen sheehy
Posted Aug 13, 2014 8:21 AM ET


I used 3" XPS under my basement floor and didn't tape the seams, we did however ensure we taped the seams of the poly vapor barrier extremely well.

Answered by Anthony Hughes
Posted Aug 18, 2014 11:54 AM ET

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