Insulation, Radiant and Vapor Barriers - Window dormer with limited cavity depth.

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boris111
04-22-09, 01:17 PM
Hello I'm finishing my attic. I have small window dormers on the front of the attic. These were constructed such that I only have a cavity depth of 1 1/2". That is my only option for depth as I would block the window if I make them any deeper. Should I put in R13 and compress it against the sheetrock, or I was thinking of cutting the Polystyrene between each one. Which would give me the best R-Value?

Bud9051
04-22-09, 02:34 PM
The foil faced polyisocyanurate will give you the best results. R=7 per inch and seal it in place really good.

here is a link for you:
Welcome To Home Energy Magazine Online (http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/95/950309.html)

Bud
boris111
04-22-09, 04:15 PM
What do I use to attach it? Glue?

Bud9051
04-22-09, 05:10 PM
press fit or glue, either works. If you have any space at all on the inside, add a layer of fan-fold or 1/2 inch foam, as much as possiple to cover the wood framing. If possiple?

Bud
boris111
04-23-09, 12:08 PM
Thank you very much. I'll see what I can do about covering the 2X4's as well.