Replies

1. 
   Neilc1 | Aug 18, 2015 10:12am | #1

   Should be more informative,I got enough of this 1" Xps roofing board for free and have put it up against all my poured concrete walls,now I am ready to stud the walls and then Sheetrock,I know it's not the best but the price was right and I talked with Owens Corning and they feel I should be ok with it but wanted a other opinion,I actually got enough to double it up on some walls to make 2",so minimal 1" plus 4" of batting should give me a descent r value

2. GBA Editor
   Martin Holladay | Aug 18, 2015 10:22am | #2

   Neil,
   I think you forgot to tell us your location or climate zone.

3. 
   Neilc1 | Aug 18, 2015 10:53am | #3

   Massachusetts zone 5 I believe

4. Expert Member
   Dana Dorsett | Aug 18, 2015 11:10am | #4

   Tape the seams and can-foam the edges, and yes, R5 XPS is sufficient for dew point control on the above-grade portion for up to 2x4/R15 without interior vapor retarders in zone 5. The ~1-1.5 perm vapor retardency is a sufficient vapor retarder against ground moisture for the below grade portion, assuming it's a reasonably dry foundation wall (no history of bulk water leakage of that wall.)

   And, 1" XPS + 2x4/R13 would meet the IRC code-min performance equivalent to R10 continuous insulation for basements in zone 5.

   http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_11_sec002.htm

   In MA there are multiple vendors of reclaimed roofing foam. It may be cheaper to go with 2-2.5" everywhere than to use batts in the studwalls. Nationwide Foam in Framingham and Green Insulation Group in Worcester are probably the biggest, but there are others.