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Community and Q&A

Attic Air Sealing

hpnWsbX6gm | Posted in General Questions on

Hello,

I was wondering if there was a way to easily air seal an entire attic?

The attic is vented and unfinished with fiberglass batt insulation. The insulation and air gaps are located beneath a wood plank floor that has been nailed down. If I wanted to air seal the traditional way I would have to pull up all of the floor boards, the insulation, and then find and seal all of the gaps. Is there an easier way to to air seal over the gaps, existing insulation and wood floor?

I was thinking of putting down a layer of foam board, taping the seams, and then blowing cellulose on top of this. Will this work? How will I seal the edges? Would it be possible to use a wrb such as Tyvek rather than foam?

If anyone has any experience or ideas regarding this it would be appreciated. Thanks for your time!

~Graham

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Graham,
    Interesting question. The best way to proceed, of course, is to pull up the floor boards. But if you are willing to experiment ....

    You could unroll Tyvek or Typar over the floorboards, and carefully tape the seams with Tyvek tape. The problem is the perimeter. You would need, I think, to get one of those two-component foam kits (a Handi-Pack kit) to foam the perimeter, sealing the Tyvek to the perimeter wall top plates. All penetrations — chimneys, plumbing vent pipes — would also need to be foamed to the Tyvek.

    After that, you could blow in cellulose on top. If you were meticulous, the plan could work.

  2. Doug McEvers | | #2

    The other option is to pull up the floor boards as discussed, remove the batt insulation, check vents and windwash protection then spray the entire ceiling (attic side) with a layer of closed cell foam. This may be a bit pricey but if there are a lot of air leaks this method would take care of it. Add blown insulation of your choice using hdd/120 as a guide.

    This is what I would call a "hot top" method, by really sealing the attic bypasses a good share of the home's infiltration will be stymied.

  3. hpnWsbX6gm | | #3

    Thank you for the advice. This is an old home converted to a 3 unit apartment building. I am responsible for paying the heat so increasing efficiency is paramount. Located in VT, 8500HDD climate. I considered spray foam for the whole thing but this was beyond my budget.

    Where exactly on the top plate would I foam seal the tyvek? Would I cut it around the rafters. staple it down to the plate, and then foam the whole area? I think I would also need to install some baffles before this step.

  4. Riversong | | #4

    Graham,

    That's the problem with your plan. With all the intersecting framing at the eaves (ceiling joists, rafters, wall plates) there's no easy and reliable way to create an air seal other than using lots of foam sprayed up against ventilation baffles.

    I think you will find it easier to pull the floor boards and air seal the penetrations with a few cans of spray foam, reinstall the batts and blow cellulose on top with vent baffles at the eaves.

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