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Community and Q&A

Is it possible to satisfactorily detail single layer of exterior xps square edge sheathing?

Daniel F. Vellone | Posted in Green Building Techniques on

Having been directed to an insulation reclaimer I have the opportunity to purchase enough reclaimed xps to sheath my exterior frame though only with a single layer since the 2.5″ panel thickness satisfies my requirement. Timberframe has a 2×5 (full dimension) exterior frame that gets cellulose densepack and sheathed with xps that will get 1×4 strapping prior to siding. This foam is square edge and I’m wondering if, in the absence of multiple layers with staggered seams as well as t+g edges, the detailing to adequately seal the seams of the xps will be possible or even approachable.

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  1. User avatar
    Dana Dorsett | | #1

    If the stuff is pretty clean you can seal the seams with housewrap tape and it will do fine. If it's dirty / dusty enough that tape adhesion is a problem, going over the tape with duct mastic at the edges will take care of it. One aspect of reclaimed goods is that the long term shrinkage issues will be lower than with virgin stock goods, which means any gaps that open up over the next few decades will be small. If sealed with a good tape, the net impact of those gaps on overall performance will be small.

    From a dew point control point of view the gaps would not matter at all.

  2. User avatar GBA Editor
    Martin Holladay | | #2

    Plenty of people use a single layer of foam. Use common sense to seal air leaks.

    If you don't want to follow Dana's suggestion to use tape, you can use caulk and canned spray foam -- caulk for the narrow joints, and canned spray foam for the wider joints.

  3. Daniel F. Vellone | | #3

    Thank you for the very helpful advice.

  4. User avatar
    Dana Dorsett | | #4

    With can foam on less-than-clean XPS, use an always flexible "windows & doors" variants. I've seen the stiffer standard grade can-foam separate from grungier XPS & EPS when filling big gaps.

  5. Daniel F. Vellone | | #5

    I made the jump and purchased the reclaimed xps from the Mayfield reclaimer. Appreciative for the tip and good advice.

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