Is it necessary to tape joints in under-slab insulation?
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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.
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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.
Thanks, Dana-That's what I hoped was the case. Your explanation makes sense.
You doing one layer of 4" or 2 layers of 2"? Good to have staggered seams.
Dan-we're using 4".
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.