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Sealing the ceiling prior to blower door testing…

user-1012653 | Posted in Energy Efficiency and Durability on

I know this has been covered before, but can not recover the threads after several searches.
I have a project that is in the rough in stage and is nearing completion. We want to do a blower door test prior to insulation and drywalling, however am debating the best way to seal the attic space. It is an unconditioned, vented wood truss attic. It will get 2 layers of 5/8″ eventually for fire code reasons.
My thought is to go ahead and have them install 1 layer of gyp, sealed with gaskets and caulking to create the air barrier that way. It woud be sealed to the top plates of the exterior wall, which is sealed to the exterior air battier via tape over the entire wall top plate.
Any thoughts or alternative ideas?

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  1. user-723121 | | #1

    How have you dealt with backing between the rafters? How will the air seal be continuous at this point between the ceiling and the wall top plate? I suppose if the 5/8" ceiling drywall is fit fairly tight, this gap could be caulked to the top plate. You might start the drywall at the exterior walls to have a factory edge to work with.

    Maybe some of the ADA experts will respond, us wacky Minnesotans still use poly and accoustical sealant as our air barrier.

  2. user-1012653 | | #2

    Well one thought was to use a gasket that the gyp would be pressed into against the exterior wall top plate. The gasket would extend down and double as the gasket for the wall gyp. We were considering using a 3.5" sill seal for the gasket.
    However using poly as the air barrier is also a consideration I have had. I am not too far south, in NE Iowa, zone 6. I assumed the gyp would give a better/easier seal.

  3. user-723121 | | #3

    ADA details sure seem hard to come by, the connection between ceiling and exterior walls and ceiling to ceiling via interior partitions is important. A 2 x 4 interior wall (parallel to the rafters) would get a 2 x 6 backing nailed to the top plate with 1" sticking out on each side. For exterior walls and interior partitions perpendicular to the rafters I would solid block backing between the rafters. This gives solid surfaces to gasket to, a compression seal is just that, you need something to compress to at all connecting points.

  4. user-757117 | | #4

    Have you seen the EPDM building gaskets at conservation technology?
    They have a drywall gasket (BG32) that is supposed to compress nicely without causing the drywall to bulge.

    I have used their sill gasket and "P" gasket on my own project. They're nice high-quality gaskets.

  5. user-757117 | | #5
  6. GBA Editor
    Martin Holladay | | #6

    More information: Airtight Drywall.

  7. homedesign | | #7

    Jesse, what is your climate?
    Since you are looking for a way to test your exterior wall Air Barrier BEFORE closing up the wall...
    The typical Airtight Drywall Details will not work.
    Can you describe your exterior air a wall section or photographs?
    Is this conventional framing or Double Stud wall ?

  8. user-788447 | | #8

    You say

    It will get 2 layers of 5/8" eventually for fire code reasons.
    My thought is to go ahead and have them install 1 layer of gyp, sealed with gaskets and caulking to create the air barrier that way.

    Why wouldn't you go ahead and install both layers of gyp before the rough in test? With the rough in test you are trying as much as possible to test the final whole building air barrier (which in includes all walls, ceiling/roof AND slab).

  9. user-1012653 | | #9

    I guess that is the big question...there is no exterior air barrier for the roof since it is vented, therefore the drywall ceiling is being treated that way.
    The walls are 2x6, blown fiberglass, ZIP sheathing, 2" XPS, 1" air space and brick exterior. The ZIP is taped up and over the top plate of the 2x6 prior to the trusses set. I was going to continue my exterior air barrier to the ceiling plane with sealing the gyp to the top plate.

  10. user-1012653 | | #10

    J Chesnut-
    Yes, I realized it did not make much sense to only do the single layer. I will have them install both layers prior to testing....assuming installing the gyp now is the best way to do it (verse say plastic VB, etc).

  11. user-723121 | | #11

    Pre-final blower door testing is a good idea if it gives one the ability to seal leaks in the building envelope, I don't know about an ADA system and how this would be accomplished. I had a conversation a couple of years ago with Gary at TEC about pre-testing homes that use polyethylene as the air barrier. We agreed that depressurization would not work as it would pull the poly away from the wall, so instead a slight pressurization would be best. I suggested a theatrical fog machine to see where the air leaks were and Gary said they had one and had used it to find bypasses in multistory commercial buildings.

    This may give some insight on how to test buildings for airtightness before the drywall is complete.

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