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ChrisO 01-27-2007 01:50 PM

Cathedral ceiling without sofit vent on one side
I am finishing a room above my garage and am trying to figure out how to best insulate the cathedral ceiling. On one side of the room, the rood if pitched at at 45 degree angle and has soffit vents. On the other side of the room, there is a large dormer, and the area that isn't taken up by the dormer has the same 45 degree angle, but on this side, there are no soffit vents. Another complication is that the ceiling is only constructed with 2x8s instead of 2x10s or 12s so the standard R-30C or R-38C insulation with a baffle won't fit in the celing as is.
So, my question has a few parts. I live in Rhode Island so I would like at least R-30 insulation in the ceiling. My thought was that I would put in two layers of high density R-15 insulation in with the baffles. This way I could get the R-30 rating and still have room for the baffles against the roof. Would the two-vapor barriers cause any problems with moisture? My other option would be just to stuff R-30C in the space with a baffle and loose some of the R value due to compression. Also, on the side of the room with the dormer and no baffles, do I need to put in any baffles on this side since there are no vents on the bottom? Or could I just put in the R-30C insulation right to the roof? Thanks in advance for your help. Any insight to my conundrum would be really appreciated.

redline 01-29-2007 08:06 AM


Originally Posted by ChrisO (Post 31442)
Would the two-vapor barriers cause any problems with moisture?

Use only one vapor barrier. Remove the other vapor barrier before install.

Have you thought about spray foam insulation?
Some have a higher R-value per inch then batt insualation.

ChrisO 01-29-2007 09:24 AM

how about sides with no soffit vent?
Thanks for your reply, I really appreciate the help. Removing the vapor barrier from the innner layer of insulation seems like a good suggestion. I have considered spray foam insulation, and I even got an estimate, but right now I think it is a bit too expensive for my budget.

How about insulation on the side of the roof with no soffit vents at the bottom, are baffles needed between the roof and the insulation? I guess another way to ask the quesiton is, is it always necessary to have baffles against the roof no matter if there is no air supply from the bottom? With the size and shape of the dormer, there really isn't any place to put soffit vents, except for maybe a foot or two in the far corners of the building. I suppose some air supply could come from the top above the ceiling and from the ridge vent.

Thanks again for your help.

AaronB 01-31-2007 10:51 AM

Foam insulation pays for itself in short is the best long-term hassle-free option available. A 2# density foam will give you r 30 with 5 inches AND create its own air seal.

If youre willing to do allthis work, how much more can the insulation installation cost?

Send me an email, I have more info for you.

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