Slope wall/roof in between the knee-wall & ceiling joist,…
I thought about using 3/4″ foam cut tightly to fit in between the joist with 1″ clearance between the foam and the underside of the roof decking,…and then insulate w/ faced fiberglas batts (R30) stapled to the rafters…
Would this create a problem having two vapor barrier’s?
I’m open to any suggestions…
paul
Replies
Paul, your post lacks a lot of detail.
Is the ceiling above whatever this kneewall abutts insulated?
Is this vent you are constructing going to a ridge vent?
New construction? Attic conversion? What are you doing?
Way too many unknowns to guess at an answer.
Joe H
Thanks Joe...
It is new construction
1&1/2 story
the slope wall/roof in question is in fact the roof rafters in between the knee wall & ceiling joist...
above the rafters will be the metal roof ...&... above the ceiling joist is the attic.
I like the idea of the rigid foam & fiberglas combination, but i do not know if it would create a moisture problem having 2 vapor barriers
hope this helps...
thanks paul...
Do you have a vented roof?
If not, dense pack it with cells and you're done.
And warm.
And quiet.
Joe H
I wouldn't consider my words as weighty as the other but.........I just used cellose for the first time in walls last weeek. Boy was it easier. I needed the cellose because I used foam on the outside of the walls and needed the condisation to dry to the inside. Usually a wall dries to the outside. So If I couldn't use standard FG with the vapor barrier. The only mistake I may have done is used a corrigated hose instead of a vinyl hose. It packs tight enough you can't pull the hose out (I drilled a hole at the top of the wall and snaked a hose down) So it may not have packed as tight as it could have.
Your discription of your problem isn't clear. Cellose doesn't provide a vapor barrier issue if your worried about condisation
I did an attic this summer,similar situation. I installed propavent (or something similar) on the underside of the deck between the rafters to vent the roof. Then installed unfaced batts below that, and finally, rigid foam on the underside of the rafters. Tape and seal the foam layer and there's only one vapor retarder (on the conditioned side of the roof where it should be). If you are drywalling the ceiling, you can run furring over the foam panels.
I did something similar with 2" board in my attic but don't think it's possible to get it "tightly fitting". Cut it with a 3/8" gap all the way around and foam it in place with Window and Door variety of Great Stuff.
Steve.