# Insulating an attic framed with 2x6



## dustycreek (Sep 9, 2012)

I'll add, alternately I'm now considering instead going with 1" (or whatever is common) foam baffles and then as much fibreglass as I can fit in.. guessing R20 is probably too much unless I peel some off.


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## Windows on Wash (Aug 30, 2011)

It is pretty well thought out, however, I would plan on covering the rafters with rigid foam prior to drywalling. They will still be super cold in this application and in that climate, you will have some condensation issues.

Rip down some 1.5" foam board and apply those strips to the underside of the roof deck to create continuous vent channels. Fill the rest of the rafter bays with rigid foam cut to fit the width (do not use fiberglass). Seal all the seams with sealant/foam for air seal. Cover the rafters with a rigid foam to eliminate the thermal bridging and cold rafters. Cover with drywall.

This should give you the best assembly and still maintain the venting. 

You will not need a vapor retarder if you use the right foam board and how much you cover the rafters with will determine your final R-Value. 

I would not put less than an R-38 in that assembly. 

Air seal and kneewall floor. Blow in additional insulation. Install joist blockers. Foam seal the kneewall and back with rigid board as well.

Air seal the top attic floor. Blow in R-50.

:thumbup:


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## Gary in WA (Mar 11, 2009)

Well said! ADA the drywall to seal the knee wall cavities on room side (esp. around electrical boxes) and caulk the wall/floor joint (required in U.S. Codes now), weather-strip the attic access opening; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_11_sec002_par021.htm

http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/

Gary


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## dustycreek (Sep 9, 2012)

Thanks for the replies guys, and the detailed write up Windows On Wash. I'm going to cost everything out and decide what to do.


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