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Discussion Starter · #1 ·
I'm planning to do 2"XPS in the basement framed over with 2x4's. However 2" XPS only has a R-Value of 10 and my code calls for R11.

What is the recommended procedure to get to R11?

I see some people doing unfaced batts and others saying batt insulation does not belong in a basement.
 

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I would use ROXUL in the basement,2 by 4 construct would give you R-25 (10 from the XPS,and 15 from the ROXUL),seems like overkill unless you live in like Nome or something.
How about putting a vapor retarder on the walls (Drylock or the like) framing within a half inch of the walls (but not touching),then stuff the cavities with ROXUL.
XPS is a great vapor barrier,but its pretty expensive.
 

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I would use ROXUL in the basement,2 by 4 construct would give you R-25 (10 from the XPS,and 15 from the ROXUL),seems like overkill unless you live in like Nome or something.
How about putting a vapor retarder on the walls (Drylock or the like) framing within a half inch of the walls (but not touching),then stuff the cavities with ROXUL.
XPS is a great vapor barrier,but its pretty expensive.
Drylock? :no:

2" XPS is expensive. 1" is more manageable.

Your poo pooing the extra cost of XPS but recommending Roxul???

B
 

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1 good thing about ' drylok ' type mtls is that you can color them by buying pigment from sher-wms,,, 1 more is that when they fail its easy to see the damage :furious: ooops, guess that's 2 :eek: its always easier doing moisture test BEFORE starting to spend $ & invest labor
 

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Discussion Starter · #6 ·
I have been reading that 1" foam is not sufficient to act as a vapor barrier. It must be 2" minimum. Is that an accurate statement?
 

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hang 6mil plastic sheeting & don't worry about vapor,,, conc OR block, you won't have to worry provided the exterior's been properly waterproof'd,,, bldg code ONLY requires 3mil dampproof coating tho :furious: hardly sufficient impo
 

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I have been reading that 1" foam is not sufficient to act as a vapor barrier. It must be 2" minimum. Is that an accurate statement?
Somewhere in one of the many links that GBR provides from Building Sciences (in the Insulation section) there is a statement that you can get by with 1" if the humidity levels stay low enough in the summertime). I can not provide that for you now, but do a little more searching in that section and see what you find.

B
 

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I think I answered your R-10 already.... R-11 is not in the Codes for continuous insulation for a basement, your inspector is wrong; Chicago, IL; http://www.reedconstructiondata.com/building-codes/illinois/ SO, IECC 2009 is your state-wide code with no local amendments...from that link.

Under that code, 10/13 is required in a basement;

"c. "15/19" means R-15 continuous insulated sheathing on the interior or exterior of the home or R-19 cavity insulation at the interior of the basement wall. "15/19" shall be permitted to be met with R-13 cavity insulation on the interior of the basement wall plus R-5 continuous insulated sheathing on the interior or exterior of the home. "10/13" means R-10 continuous insulated sheathing on the interior or exterior of the home or R-13 cavity insulation at the interior of the basement wall." From; http://publicecodes.cyberregs.com/icod/iecc/2009/icod_iecc_2009_4_par004.htm

http://www.rssweather.com/climate/Illinois/Chicago/ Averaging your low temps for Dec, J, F = 7*F With 1" XPS (R-5) your foam, inside face would be 31*F at "frost line" and above grade, using R-15 (Roxul) 3-1/2" thick at 70* room temp. with 23% RH (room air) giving condensation there.

With 2" f.b., 39*F f.b. temp., safe up to 32% RH at 70*F, much better...

Gary
PS. MN with 42" "frost depth" and above grade--- 1" f.b and f.g.= condensation at/above 18% RH, need to dehumidify the basement air.
 
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