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Community and Q&A

Sill gasket

Jim Orasky | Posted in GBA Pro Help on

I’m currently planning on using an EDPM gasket under my sill plate (new construction). I’m also planning on using sprayed close cell to fill/seal the rim joist on the basement side. Since the main purpose of the sill gasket is air-sealing, is it really necessary if I do a quality job with the closed sell spray?

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  1. Tobias Richon | | #1

    Yes. Some type of sill seal is necessary. The main function of the sill seal is to create a capillary brake between the the foundation and the wood sill.

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

    Tobias is correct about the importance of having a capillary break. Moreover, a redundant air seal at this location is a good idea; spray foam alone is not as dependable as spray foam plus sill seal.

    Some builders even add a third leg to the stool: they caulk the joint on the interior before installing spray foam.

  3. Aj Builder, Upstate NY Zone 6a | | #3

    Laser level check, shims, leveling concrete, span lows with rim, blue sill seal, caulk as needed done.

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