Frost In Attic, Fixabe During Winter?

Old 01-11-17, 08:58 PM
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Frost In Attic, Fixabe During Winter?

Hi there, bit of a read, apologies in advance, but I've tried to give all necessary details.

I'm in Southern Ontario, Canada (near Toronto) and bought my current house a couple years ago. It's a semi-backsplit and was built in the early 80's, so 30-35 years old. I'm doing a renovation on my main floor, a 400 sq ft kitchen / living area. I gutted the entire main floor, removed all cabinetry, drywall, insulation, flooring, etc etc, except for the ceiling drywall, of which my attic space is above. I've picking away at it on weekends, and am getting near to the drywall stage, but have run into two problems, both discovered because the cold weather has arrived:

1) The first problem was that once I finished with a wall, I was adding the insulation (pink fiberglass batts for 2x4, 16" OC). Since I was still working on adjoining walls, I hadn't yet added the vapour barrier / drywall. This was fine at first, but I wasn't able to complete everything before the cold weather arrived.

One day a few weeks ago I went and put my hand behind one of the batts to see how cold it was, and found out it was wet back there. I started pulling out some of the batts and discovered water or frost behind them on the exterior sheathing (an exterior drywall). I figured it was because of the indoor air / humidity getting behind there from not having the vapour barrier and drywall up yet.

I removed all the insulation, dried the walls out, and turned the humidity down (40% to 30%). Since I caught it early enough, there doesn't seem to be any permanent damage to the sheathing, and most of the insulation looks reusable (no clumping). I've kept the insulation off and I haven't seen any frost return. I won't put it back until I'm ready to insulate / vapour barrier / drywall all in the same day, but I just wanted to check that I'm not overlooking anything and can proceed as planned.

2) I had to go into the attic last weekend when it was around -10C outside, and discovered that most of the tips of the roofing nails sticking through the plywood were coated in frost, as well as some areas of the plywood having frost on it. It wasn't an extreme amount, and I don't have any pictures, but somewhere in between the two of these:

There are no signs of rot or mold, so it doesn't seem like something that's been happening up there year in / year out, and I had the roof stripped and re-shingled 2 summers ago.

About the attic:
- Roughly half the ceiling drywall was pulled down (kitchen side) and I put in new vapour barrier / drywall (5/8" Type X).
- The other half is original drywall / vapour barrier, which is really thin in comparison to the new 6mil poly, and probably has tears / bad seals in it from age.
- There's currently only about 4-6 inches of blown-in fiberglass insulation. My plan was to add to it after I finished the renovation, because of having to go in and out for the lighting and venting.
- The roof for this attic space has two gable sides. The third side is connected to the neighbors, and the fourth connects to the back half of the house.
- Because of the roof configuration, the ventilation isn't that great. Since there are no eaves, the only spot air comes in is the front porch, a roughly 4'x6' area with probably a 5-6 sq ft vent hole cut out. There are 3 vents on top, no ridge vent.
- Couple of pictures below after the roof was done, and the attic before drywall:

Anyways, I figure the problem is again that because I have all the walls gutted the indoor air / humidity is getting up there through the cavities and any other areas not sealed / mudded yet. My questions are:

- Should I continue with my current plan of getting the walls finished with insulation / vapour barrier / drywall, and that should solve (or mostly solve) the problem? I would also be able to do some additional sealing from the attic side when I dealt with the insulation after the renovation.

- Should I pull down the rest of the ceiling and put in new vapour barrier? I wouldn't want to find out I need to do this later on, and have to rip things apart once the walls / paint / kitchen is all done, and I'm not sure how easy it would be to vapour barrier from the attic side, overtop of the truss bottom chords, if even possible...

- If I should pull down the ceiling, could I still wait to add insulation until all my work is done up there?

- Regarding insulation, should I be looking at blown-in fiberglass or something like cellulose? Doubt I could afford spray-foam.

- If I should pull down the ceiling, is that something I should do during winter? My time is limited so it wouldn't be something I could just knock out in a day or two. There would be half a ceiling with no drywall / vapour / insulation for a period of weeks, and I don't know if that would make things worse. Maybe not inside, but certainly outside if the snow were to come, I could have troubles with ice damming in the valley from all the heat escaping.

- Is there any solution I should look at for additional venting, or should what I have suffice? The only options I can see are adding something on the gable sides for intake, or increasing the cutout for the porch soffit. More outtake vents could be added as well if needed.

Any advice is much appreciated, and if I can answer any additional questions, let me know. Thanks!
Old 01-12-17, 06:19 AM
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I've kept the insulation off and I haven't seen any frost return. I won't put it back until I'm ready to insulate / vapour barrier / drywall all in the same day
You've got the right idea. A little minor frost (like on the roof deck) is not a problem. In my climate, latest thinking is that latex paint on drywall is the only vapor barrier you need. (Class III vapor retarder.)

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