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Top plate vs. 1 x 3

user-6828388 | Posted in General Questions on

I’ve spent hours reading and cannot find the answer to this simply question. How broad is the definition of a top plate? For example in my attic there are top plates at the top of interior and exterior walls. I’m wondering if air sealing also needs to be done where the drywall is nailed to 1 x 3’s? Are these 1 x 3 drywall supports also called top plates?

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  1. DIYJester | | #1

    These are probably actually pieces of wood nailed to the top plate so that they could hang the drywall near the edge of a room without a truss near it.

    Many here have suggested that this area also be sealed just like other openings into the home's envelope.

  2. GBA Editor
    Martin Holladay | | #2

    SciFi Jock,
    It sounds as if your ceiling is strapped with 1x3s (installed perpendicular to the ceiling joists). This approach is common in the Northeast. It's still possible to get air leaks at the tops of interior partitions. Imagine all the warm air inside the stud bays of your interior partitions, trying to escape into the attic. Attack the cracks.

    A photo might help.

  3. user-6828388 | | #3

    Here is a photo of the strapping and you can see the top plates that I have air sealed. Is this strapping the drywall is nailed to considered a crack in the air boundary? This is a tight space and not a lot of room to move the cellulose out of the way, but I will do it if it is a large air leak.

  4. GBA Editor
    Martin Holladay | | #4

    I can't tell what's going on from your photo. It looks to me like your house used to have a board ceiling. Is that possible?

    Can you do a better job of describing what's under the existing insulation?

  5. user-6828388 | | #5

    This is a 1940's house. It may have had board ceilings, but they are drywall now and the boards may have been removed.

    The black material that you see I think is an old bat insulation that has tar paper on both sides and some wood shavings or something like that inside. It's very thin less than 0.5 inches. This is nailed to the strapping and the drywall is nailed below that. The black material is continuous and may be a decent air barrier.

    In the new photos I ripped up a section of the black insulation and you can see the drywall under it. I also tried to give a close up of the insulation. I've never see anything like it before.

  6. GBA Editor
    Martin Holladay | | #6

    Your explanation and the new photos are helpful. It looks like you have two types of insulation: some type of wood shavings (a little bit orangey) and cellulose (gray).

    Your drywall ceiling is attached to 1x3 or 1x4 strapping. As long as you address air leaks at the top plates, you don't have to worry about the strapping. In other words, seal the cracks near the top plates -- but don't worry about the gaps on each side of the strapping.

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