I was working at a house the other day and noticed big icecicles hanging from the gutters. I went into the attic and found insulation in the ceiling from below with wood covering the joists. The roof only had about 1″ of fiberglass in it.
The roof has all the snow melted off until it hits the soffits where it’s freezing. The attic is heated on one side where there is a dormer. The unfinished side was also about 50 degrees.
I was going to put styrofoam baffles in the roof and put r19 over that. I figured that would allow the cold air from the soffits to stay under the sheathing and keep the roof cold. Does this sound like it would prevent the roof from melting and causing icecicles?
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Depends upon what the rafters are. If you have 2x6 (like mine), I put in the Owens Corning baffles (the pink ones you get at HD) for venting (I'm ASSUMING you have a ridge vent?).
Then put Owens Corning high density fiberglass (I THINK it's R-21). But still left me short the R-25 minimum our local building codes require. So, they said I could put 1" foamboard on that (obviously over the rafters) at an R=5, so that got me in theory, an R-26. Seal with tape and it should actually work pretty good.
Others here may have better ideas.
"[T]hey said I could put 1" foamboard on that (obviously over the rafters)..."Did AHJ allow you to do this without putting a thermal barrier over the foam? I've considered doing something like this (walk-up attic, air handler in attic), but I doubt my undersized rafters could take the additional weight of DW....
In my case, I have a cape code, so the roof is a 12 on 12 pitch.There's a 4' 6" knee wall, so no drywall behind the kneewall on the "roof". Just the sealed foamboard. I also have R-38 densepack cellulose in the floor of the 2nd floor (or in the ceiling of the 1st floor).then I have the section of "roof" above the kneewall to contend with. They let me put the sheetrock on top of that (which is on top of the 1" foamboard). I think that was also 4' 6" worth until it met my 7' 6" ceiling.I would think a 2x6 should be able to hold 1/2" sheetrock without a problem. Granted, mine are 16" on center for the rafters too. Hope this made sense.
As Hurnik said. It might. An additional thing to do is to seal any opennings between the living area and the attic space. Every hole is an avenue for air that you have heated to blow into the attic.
This heat is mostly responsible for the snow melting.
Get some cans of foam and crawl around: anylight fixture/ceiling fan in the ceiling below probably has holes around and in the electrical box...don't fill the box with foam, but get the holes sealed. Any ducts making their way through the attic probably have opennings around them where they pass through the ceiling (but if it is a duct that is going to get hot or a chimney, use metal and a caulk suited for high temp use.
Check the tops of the walls and seal between the top of the drywall and the topplate of the wall.
Wherever wiring comes through the top plate, that hole should be sealed around the wire.
If there are can lights, but careful. Some can lights are not rated for contact with insulation. In that case, you need to fabricate a roomy box to fit over the light...drywall is a good material to use, and you can seal the edges with mud or foam and then foam it to the "floor" around the light (foaming shut the hole the electrical line uses).
Rich Beckman
Another day, another tool.
"Does this sound like it would prevent the roof from melting and causing icecicles?"
Unlikely to help much. You would need a more comprehensive approach to controlling convective airflow out the top of the structure. Need to decide where the weather perimeter is; floor or ceiling of unfinished space? Wall between finished and unfinished space? Does finished space have a kneewall? Do you intend to gut the finished space? Lots to consider.