Author Topic: Help sealing a vapor barrier  (Read 588 times)

FLBiker

  • Handlebar Stache
  • *****
  • Posts: 1786
  • Age: 47
  • Location: Canada
    • Chop Wood Carry FIRE
Help sealing a vapor barrier
« on: January 18, 2021, 06:43:09 AM »
Hello - we recently purchased a house in Nova Scotia and the vapor barrier in the attic crawlspace isn't sealed. It seems as if it wasn't quite wide enough, so the top edge isn't sealed in any way. I'd like to run a second strip to seal it and I wanted to confirm my plan.

My thinking was that I'd use blue tuck tape to attach the new strip to the existing vapor barrier, and then run boards between the studs along the length of the crawlspace and seal the other side of the barrier to that board with acoustic sealant.  Without running the boards, I'm not sure what I would seal it to (which is why I assume it wasn't sealed in the first place).  Does that seem reasonable? I've never worked with vapor barrier before.

Also, the bottom edge of the existing vapor barrier is sealed just by stapling it to the wood. Is that OK, or should I pull that off and use acoustic sealant there as well? The house stays warm, but we've noticed some drafts around the crawlspace.

I've attached pics of the top and bottom edges.  Thanks!

FLBiker

  • Handlebar Stache
  • *****
  • Posts: 1786
  • Age: 47
  • Location: Canada
    • Chop Wood Carry FIRE
Re: Help sealing a vapor barrier
« Reply #1 on: January 18, 2021, 07:42:01 AM »
Here's a better picture of the space.  It's insulated on the roof side and it isn't insulated facing the house. The tricky part is the top of the triangle, where the angle from the roof comes into the wall of the house -- there isn't a great piece of wood to seal to, because it's basically just wall studs. Thus, I'm thinking I'd run boards the length of it to give me a surface to acoustic to. Does that make sense? Alternatively, I could seal it to the edge of the top plate.

J Boogie

  • Handlebar Stache
  • *****
  • Posts: 1531
Re: Help sealing a vapor barrier
« Reply #2 on: January 18, 2021, 08:40:22 AM »
I think you'd probably be fine if you simply cover the joint with vapor barrier sealing tape, probably 6" or 8" width should give you enough coverage.

Might be tricky sneaking it into a corner like that but you could staple/tack some foam backer rod into the joint to make it a little easier.

Applying enough pressure to the tape on the poly-covered insulation between the studs might be tricky but the additional inches of tape width should give you some breathing room to push hard without fear of tape failure and sticky mess.

zolotiyeruki

  • Walrus Stache
  • *******
  • Posts: 5603
  • Location: State: Denial
Re: Help sealing a vapor barrier
« Reply #3 on: January 19, 2021, 09:39:38 AM »
A couple thoughts come to mind:

1) Could you ham-fist a seal between the top of the plastic and the wall using foam in a can?  That stuff sticks like the dickens, forms a great air seal, and tolerates imperfect application.

2) If you're chasing drafts, it may be worth it to rent or borrow a thermal camera.  I did that a couple weeks ago to help locate air leaks in our attic, and it made the job super easy and fast.

FLBiker

  • Handlebar Stache
  • *****
  • Posts: 1786
  • Age: 47
  • Location: Canada
    • Chop Wood Carry FIRE
Re: Help sealing a vapor barrier
« Reply #4 on: January 20, 2021, 12:05:48 PM »
Thank you both for these replies!  I've been fixated on doing it "right" in terms of following code up here -- which is acoustic sealant to wood, blue tuck tape when it's plastic to plastic.  Realistically, though, I think both of your ideas would likely work (and be easier).  Thanks!

And re: the thermal camera, it's a good idea.  We had Efficiency Nova Scotia come out and they did some testing, and this gap was the only real source of outside air.
« Last Edit: January 20, 2021, 12:08:16 PM by FLBiker »