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Partitian wall top plates are concealed by second layer of drywall

SouthDakotaRoof | Posted in Energy Efficiency and Durability on

My home is from 1953. Even though this is a cold climate it has no insulation in the walls. I believe the original builder thought drywall was insulation enough because walls and ceiling are both two layers of drywall in full contact with eachother. I’ve been airsealing the attic floor. I’ve been plugging away at the exterior top plates, lights, etc.. however the partitian wall top plates do not come up to the second layer of drywall on the attic side. I figured the walls were either raised after the ceiling went up (sealed up then!) Or the went through the 1st layer and then covered over by second layer (sealed up then too!) Win / win situation, ya? Nope. Attempted diy blower test with flir c2 thermal camera. I was surprised to see the creeping tendrils of cold air inflirtration at those top plate areas. What can I do about that? Google has 0 hits for this situation.

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  1. Expert Member
    Akos | | #1

    You can brush the seams of the drywall with duct mastic. If you don't have any, you can pick up a small bucket from most HVAC suppliers. Use a stiff brush to brush it on. Make sure the surface is somewhat dust free. For extra performance, put fiberglass mesh tape before brushing the mastic on.

    1. SouthDakotaRoof | | #2

      The drywall seams on that second attic side drywall? Sweet, I have already been caulking those. But mastic is better ya? No problem I have plenty of mastic, I've been using it to seal the very uneven exterior wall or maybe it's a cladding? Whatever it is that is just over the top plate and coming up the wall in the soffit.

      1. Expert Member
        Akos | | #3

        Mastic is just easier on the arms. After a hundred feet or so of caulking, one tends to look for alternatives.

        Unless you are conditioning your attic, you don't need to seal up the soffit area, you only need to seal up your ceiling and wall top plates.

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