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Air sealing at top plate

Chad_Attermann | Posted in Energy Efficiency and Durability on

I am owner-builder on an extensive remodel where the entire above-grade structure above the floor joists is being replaced. After extensive planning and research prior to start of construction, I was off to a good start on air-sealing details with EPDM gaskets under the sill plates, and acoustical sealant on-hand for sealing sheathing to the sill and top plates. However as I feared, at some point the framers forgot to apply the acoustical sealant on some large sections of wall, and now I’m uncertain exactly how to air-seal at the top and bottom of the walls.

I am considering some sort of self-adhered flashing at the bottom to seal the sheathing to the foundation which I can seal the WRB to. I can’t think of any way however to effectively seal the top of the wall and make it continuous from the sheathing to the air-tight drywall in the ceiling. I think switching to an unvented roof and spray foam might be a solution, but that would really strain the budget and therefore may not be an option. Is there another way to make the air-barrier continuous with the already installed sheathing? Would caulking or consumer spray foam from the inside provide enough of an air-seal? Am I overthinking this?

Any advice would be greatly appreciated!

-Chad

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Chad,
    Q. "I can’t think of any way however to effectively seal the top of the wall and make it continuous from the sheathing to the air-tight drywall in the ceiling."

    A. You should read this article: "A Practical Air-Sealing Sequence."

    1. Chad_Attermann | | #2

      Thanks for the reply Martin. The link you referred me to is actually the method that I was aiming to follow, however the opportunity to seal the sheathing to the top plate was missed (unless I insist that the framers pull off the top row of sheathing and re-apply with adhesive).

      Any thoughts on how to achieve a reasonable seal after the fact?

    2. fourforhome | | #6

      When using a plywood cap plate, is a SDWC Truss screw used in place of a hurricane clip?

      1. Expert Member
        MALCOLM TAYLOR | | #7

        Mark,

        You can use the screws, or mount the truss-clip on the exterior.

  2. GBA Editor
    Martin Holladay | | #3

    Green,
    Q. "The opportunity to seal the sheathing to the top plate was missed (unless I insist that the framers pull off the top row of sheathing and re-apply with adhesive). Any thoughts on how to achieve a reasonable seal after the fact?"

    A. Tape. For more information, see "Return to the Backyard Tape Test."

  3. Chad_Attermann | | #4

    Martin, maybe I'm being obtuse but I don't understand how to carry the seal through from WRB/sheathing to the interior ceiling drywall using tape. I'm not even sure that caulking around every single stud bay and between top plates would provide a complete seal. Even spray foam sealing all around the top plates from the attic seems like it would still leak between studs and sheathing. At this point I think I'm willing to settle for just a "good enough" seal, but I'm still not grasping what that is yet.

  4. GBA Editor
    Martin Holladay | | #5

    Green,
    Q. "I don't understand how to carry the seal through from WRB/sheathing to the interior ceiling drywall using tape."

    A. You should re-read the Fine Homebuilding article I linked to. The key to the suggested method is the 3/4-inch plywood cap that cantilevers inward. The wide plywood cap goes on top of the top plate of the wall. Read the article carefully and study the detail drawing.

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