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Air-Sealing Top Plates in Attic

iainb | Posted in General Questions on

I’ve asked a variation of this question before, but I have a week off to do the work, a more specific question, and some photos.

Zone 5 (central MA), 1938 colonial style, two floors.

The attic is framed with the floor joists perpendicular to the rafters. There is a tongue and groove floor (1 x various) over the entirety. Under the floor there is cellulose insulation, then building paper, then strapping, then the ceiling.

Here’s my question:

Is it worth taking up the floor to air seal at the top of the wall plates? It’s a very difficult to remove floor. Will the existing tar paper function to seal the top plates?

If I do take up the floor and it is acting as a tie how much can I remove safely?

Thanks in advance,

Iain

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Replies

  1. adrienne_in_nj | | #1

    I looked at the pictures and what you are calling “tar paper” looks like old batt insulation to me. Very thin batt insulation. If that is the case, then I would say that it’s not doing any air sealing at all. Are there a lot of partition walls? If only a few, then you could take up the boards only where the partition walls are located. If you take up all the boards then you can use the opportunity to add more cellulose! It looks like you could use it, and if you bury the tops of the joists, that will reduce thermal bridging. This tool makes handy work of removing nails so you can pull up boards more easily. https://www.amazon.com/Crescent-56-Home-Tools-Pullers/dp/B00002N7SD/ref=mp_s_a_1_3?crid=72NFTTCWDXRT&keywords=crescent+nail+puller&qid=1660937540&sprefix=crescent+nail+%2Caps%2C85&sr=8-3
    In my own house, when I air sealed all the top plates, I brought a shop vac into the attic and cleaned out the dust before foaming because I wanted to make sure it would stick. I’m not sure if it was necessary but it sure was dirty up there and since I was investing so much time into the project, I wanted to make sure it was as good as I could possible make it.
    I have never seen a house with ceiling joists that are perpendicular to the roof rafters except where the roof is a hip roof, so that is interesting. Do you have a walk up attic? If so, that will also need to be sealed.

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