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Community and Q&A

Air sealing bottom plate to foundation

Roger_S39 | Posted in General Questions on

Hi all, 

If Siga Fentrim F 6″ flashing tape is used on the outside of the home to air seal/flash the base of the Zip sheathing to the foundation, are any of the following products/methods necessary/make any difference, and if so how?

i) The use of a sill sealer (either the pink foam or the black rubber type)?
ii) Sealing the interior base of the bottom plate with a caulk (eg: Dynaflex 230)?
iii) Can spray foam on the interior side of the sheathing where the 2×4 framing attaches to the Zip sheathing?

Thank you.

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  1. Expert Member


    1)Sill sealer is used primarily to stop moisture from wicking up into the wall by capillary action from the concrete below. it's worth including even it the sill plates are pressure-treated.
    2) Belt and suspenders.
    3) Belt and suspenders for builders with OCD

  2. GBA Editor
    Brian Pontolilo | | #2

    Hi Roger.

    As Malcolm said, sill sealer has another purpose and should be used regardless of your air sealing strategy, though the gaskets do a nice job of air sealing too. Because this is a vulnerable transition with dissimilar materials prone to movement, most high performance builders shooting for low blower door test results take redundant measures here. Many do everything that you mentioned.

  3. stuartd | | #3

    Zone 6
    I have done this: i) The use of a sill sealer (either the pink foam or the black rubber type)

    Then I taped the exterior Zip sheathing / foundation intersection with Contega Solido IQ (smart vapor control)

    For belt and suspenders, I have a lot of Siga Fentrim tape, should I use it to seal the interior base of the bottom plate (original post suggested using Dynaflex 230)? or would it be a bad idea to somewhat encapsulate the bottom plate (wood)?

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