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Community and Q&A

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

STEPHEN SHEEHY | Posted in Energy Efficiency and Durability on

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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  1. Expert Member
    Dana Dorsett | | #1

    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.

  2. STEPHEN SHEEHY | | #2

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

  3. dankolbert | | #3

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

  4. STEPHEN SHEEHY | | #4

    Dan-we're using 4".

  5. easyrider470 | | #5

    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.

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