To vapor barrier or not to vapor barrier???
I’m insulating my attic and I’m wondering about if I should use vapor barrier between my insulation and the shiplap. Q. From attic floor to lower ceiling, there is shiplad attached to joists and then drywall screwed to the shiplap. There are a few small sections of the shiplap that are still slightly damp, due to a leaky roof. Soooo, the question is… Should I lay a vapor barrier over the shiplap and then lay the insulation on top? I’ve put a barrier where it’s just drywall, like I should, but I’m worried that if I do the same over the shiplap portion in the attic, that that might not be good for moisture being trapped between the drywall and shiplap. Make sense? Please note, this is my first house and first time insulating an attic space. I just want to do the right thing, not some “homeowner special”, like the last owners did on so many other things. Lol. Thanks for any advise! E
Replies
1) Where do you live?
2) Does the roof still leak?
3) Is the ceiling well air-sealed (including tops of lighting fixtures, tops of walls, etc)?
4) How many coats of paint on the ceiling?
5) What kind of insulation will you be using and how much?
Wow, thanks for the reply!
1) I live in Vancouver, British Columbia. Canada
2) I have the main leak tarped and the smaller leaks under control too. The attic floor has been dry now for the last 2 weeks. Some of the shiplap roof sheathing is still damp in a couple spots, but I will tarp that in a couple days too. New roof to come in the spring!
3)Ceiling is well sealed, as I spend 3 days caulking the whole house when I first purchased it in September. All ceilings and light fixtures.
4)not sure how many coats of paint, looks like the usual amount.
5)I'm using the standard pink fiberglass insulation.
Thanks for replying, I look forward to hearing more from you!
-Ember
I should have asked the age of the house, too. ;)
Probably, if you have all penetrations well-sealed, a vapor barrier isn't needed there.
What's your usual minimum winter temp (lowest hit 3-4 days running most winters)?
Age 57, and winters -10
I don't feel I need to lay a vapor barrier down, but would love to hear what you have to say.
Thanks again for taking time to answer my question!
If the ceiling's well-sealed and the attic well-vented then I don't believe that you need a VB in your situation.
My guess is that with the conditions you have, it could be optional (i.e. not critical). Your attic is vented, right?
You should fix your leaks before you do your insulation. If for whatever reason, your tarp blows off, you could have wet insulation and you don't want that. You do want it dry before insulating, though.
Air-sealing is more important than vapor-sealing in your case. If you have truly caulked and otherwise sealed any possible air leaks between the living space and the attic, vapor concerns will not be an issue. The multiple coats of ceiling paint will be adequate as a vapor barrier.
Keep in mind that small gaps in a vapor barrier allow only minimal amount of vapor to pass thru, but small gaps or leaks in the air barrier will carry substantial amounts of vapor and heat into places where you don't want it. I mention this because, even if you did lay on something like 6-mil plastic under the insulation, it is not likely that you would be able to install it so as to be truly air-tight. This means that any air leaks that found their way to the plastic would also find a way past the plastic into the insulation above.
Thank you for all the replies, it's been very informative and I appreciate all of it.
Now, off to finishing my inulation!
Cheers,
Ember