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Old 07-01-2015, 09:47 AM   #1
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Insulating Above Ground Cinder Block walls


Hello,

I have been reading conflicting ideas on how to properly insulate my walls.

Details:

West Virginia (25411)
2x6 exterior studs already in place (Pink insulating foam between concrete slab and pressure treated sill plate)
8" Concrete Block exterior walls (no siding/wrap will be installed on the outside)
All above grade, floor is concrete slab

Basically no drylok type products are applied, no foam board, insulation or plastic sheeting are installed so we are starting from zero except for the framing being in place already.

My primary concern is moisture in the walls and what is an acceptable vapor barrier. Am I ok with kraft faced fiberglass insulation with the kraft paper facing the warm in winter side of the structure? Would the kraft paper be enough of a vapor resistance barrier to not induce moisture issues?

My plan was to fit as much R value in the 2x6 as possible with batts while being open to other cost effective options. At this point I don't know if rigid foam is really a possibility as there isn't an inch of space between the block wall and the back of the studs.

Any direction would be much appreciated!
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Old 07-01-2015, 09:58 AM   #2
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If you make the drywall as airtight as possible, very little is going to get through the walls and to the cold block side of the interior wall.
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Old 07-01-2015, 10:12 AM   #3
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Drywall will be professionally hung and finished, 1/2", glue and screwed to the 2x6 studs.

R21 Owings Corning 2x6 batts from home depot would be sufficient it sounds like? Are there any other options to add to that, that are cost effective or is the block thickness and the R21 insulation pretty good for my area?
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Old 07-01-2015, 11:56 AM   #4
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Put putty pads behind all the electrical boxes.

Sealing the block via some rigid foam would help with any air leakage through the block. Is the exterior painted?
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Old 07-01-2015, 12:14 PM   #5
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I can definitely do the putty pads. My only reservation with rigid foam is being able to get it between the framing and the block walls completely. I can always cut it to the size of the 16" OC studs, but i'm not sure if there's value in that or not?

Currently the exterior block is not painted at all, it's bare. We would however in the future like to paint it with some kind of exterior paint (Two sides that would be painted are 75'L x 18'H and 35'L x 18'H... Front is brick veneer so it wouldn't be painted).
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Old 07-01-2015, 01:03 PM   #6
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In this instance, when someone has a solution for exterior insulation on concrete/concrete block walls then go for it.

But until then we can attempt to seal and believe we've sealed with the best products available on the market to prevent interior air from reaching the cold interior wall surfaces but that ain't gonna happen with the technology we have at present.

It may not happen in your lifetime or while you are the building caretaker but someday the wood members in contact with the inner walls will rot and become stinky.
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Old 07-01-2015, 05:04 PM   #7
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Cut and cobbled foam in between the stud walls will help with the air barrier as well as vapor diffusion.

If you seal it to the inside of the stud wall, it will keep any warm air and, depending on the foam type, vapor diffusion to the cold block wall to a minimum.
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Old 07-01-2015, 09:29 PM   #8
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There are a few options;

1. foamboard inside the stud bays, as said already, with the addition of a moisture barrier strip over the exposed stud edges to stop solar drive (exterior diffusion) from wetting them, though top/bottom plates would be unprotected unless reachable also; http://www.buildingscience.com/docum...n-brick-veneer

As that link mentioned Kraft paper rather than poly but why paper facing vapor retarder- is it required locally? You may be under; http://www.cmdgroup.com/building-codes/west-virginia/ From there- no vapor barrier required per code if in Zone 4; http://publicecodes.cyberregs.com/ic..._14_par040.htm

Are you in Zone 4- R-10 minimum required; http://energycode.pnl.gov/EnergyCode...est%20Virginia
It wouldn't take much foam, even less than for my location- 4C; http://www.buildingscience.com/docum...mendations#Map

Another option is a spray air barrier (vapor permeable) on the block itself- if the house slab has a moisture barrier to stop capillary wicking from the wet block through slab-- also stopping the convective looping in the air space at insulation/CMU. A housewrap could also be incorporated. Or some fanfold insulation- wrap on first/last stud length of wall (vertical shingle-laps for drainage) for a drainage plane. These options are shown in detail, Figs. 4-7; http://www.buildingscience.com/docum...vapor-barriers

Another good read, sub CMU for "brick veneer"; http://www.buildingscience.com/docum...sure-guideline

Gary
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Last edited by Gary in WA; 07-01-2015 at 09:33 PM.
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