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Old 03-16-2014, 09:44 AM   #1
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Insulating Cinder Block Wall for Bedroom?


Hey all. Probably a simple question, but advice needed. Here's the situation.

--1970s split foyer home in Northern VA...Near Wash DC.
--Lower level is cinder block. Above grade in front of house, below grade in back of house.
--Extra bedroom downstairs in front (see photos!) had 20 yr wallpaper and IS ALWAYS cold! Doing some remodeling, now I know why. Builder or previous owner had 1x3 strips and 1/2" foam boards as the only insulation! Plastic sheeting is under the furring strips. Prob R-2! :-(

I will rip all of this down and frame out with 2x4s. I have insulated interior walls but not exterior and I am uncertain about vapor barriers. Given my location, do I need a vapor barrier if I use paper or foil-faced insulation. If so, where does it go?

Thanks!!!!

--Jeff
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Old 03-16-2014, 10:30 AM   #2
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Insulating Cinder Block Wall for Bedroom?


Just stick with kraft faced "that is the brown paper" and place it to the warm side. so if your home is warmer in the winter you want that paper facing to the inside of the home. The Kraft paper has butimin tar on the back of it that has a perm rating of 1.0Vapor Retarders and Perm Ratings
Insulation Facing, Kraft
1.01/4 inch Plywood (douglas fir, exterior glue)
0.7Insulation Facing, Foil Kraft Laminate
0.5Vapor Retarder Latex Paint, 0.0031 inch thick
0.450.002 inch Polyethylene Sheet
0.160.004 inch Polyethylene Sheet
0.080.0006 inch Polyethylene Sheet
0.06Aluminum foil 0.00035 inch thick
0.05Aluminum foil 0.001 inch thick
0.01
I hope showing the perm ratings helps.

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Old 03-16-2014, 10:54 AM   #3
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Insulating Cinder Block Wall for Bedroom?


When installing the kraft faced fiberglass do not staple flange faces to the inside of the 2x4 just to appease the dry wallers no matter what the so called experts say. Staple to the exposed edges where the product was intended to be attached.
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Old 03-16-2014, 12:12 PM   #4
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Insulating Cinder Block Wall for Bedroom?


The insulation that they had in there is not as bad as it looked.

Incorporating some sort of air space so the block can dry via convection isn't really that bad but the cavity should have been filled in total to the back of the drywall.

Nailbags loves foam so I would use that....SARCASM ALERT!!!......

There are some concerns if there is water that can enter via the CMU capillary action of putting insulation right up against it.

I would use Roxul in those areas.
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Old 03-16-2014, 05:16 PM   #5
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Originally Posted by Windows on Wash View Post
There are some concerns if there is water that can enter via the CMU capillary action of putting insulation right up against it.

I would use Roxul in those areas.
Thanks everyone.

I'm not sure was CMU is...or Roxul. But I was thinking of leaving the poly sheeting, furring strips, and foam boards up, then putting the 2x4 framing in front or even 1/4" in front of that. I only lose an extra 1" or so of space in the room. I think the poly and air space would provide sufficient air movement to allow the cinder block to "breathe" and keep moisture away from the unfaced back side of the insulation. Yes???

--Jeff
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Old 03-16-2014, 05:30 PM   #6
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Insulating Cinder Block Wall for Bedroom?


You are not suppose to use poly sheet and faced insulation. I have already used faced though and scored in all up with utility knife after installed. Or just use roxul insulation
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Old 03-16-2014, 06:07 PM   #7
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Insulating Cinder Block Wall for Bedroom?


I would use roxul or as it is better known Rock-wool or mineral-wool insulation. It is hydrophobic fire proof and gives a great bang for the buck. do not repeat do not double up on the vapor barrier. it is best to have unfaced insulation use a PVA primer made for having a perm less than 1.0 and you will be fine.
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Old 03-16-2014, 07:20 PM   #8
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Insulating Cinder Block Wall for Bedroom?


Sorry guys (and/or gals)...but now I'm confused. I'm hearing several different thing. I now know what Roxul is and have seen it before at HD. But it has an R value of 0! My spare bedroom gets very cold in winter with no insulation.

If I can summarize, I think what I'm hearing is to remove the poly sheet and foam board, frame in front of the cinder block with 2x4s and insulate with standard paper-faced insulation. Then drywall as usual. If the concern is to leave a small air gap between the block wall and back of the insulation, I can certainly do that.

Is that right?

--Jeff
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Old 03-16-2014, 07:32 PM   #9
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Insulating Cinder Block Wall for Bedroom?


Roxul has an r15 value in 3.5 inches.


As long as your walls are dry than you can go with your approach.
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Old 03-18-2014, 11:28 PM   #10
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Insulating Cinder Block Wall for Bedroom?


No vapor retarder (asphalt Kraft-faced batt) or vapor barrier (poly sheeting) below grade; Yet Another Basement Insulation Question

Slashing an air barrier is paramount, slashing a vapor barrier does squat; pp.5- Magnitude of vapor...; http://www.buildingscience.com/docum...researchreport
Washington, DC is in Zone 4, you require R-10 (XPS or SPF) continuous or R-13 cavity; http://energycode.pnl.gov/EnergyCode...state=Virginia

To prevent/limit condensation on the wood framing, use minimum R-5 (XPS) glued tight to CMU, at least above/2' below grade; then R-13 in cavity, OR, R-10 and no cavity insulation. If you go no FB and cavity fill only, remember the air gap requires fire-blocking 10' horizontally and at top to joists above; http://publicecodes.cyberregs.com/ic...002_par017.htm

BTW, Roxul (fibrous insulation) is also susceptible to loss of R-value when wet; http://www.google.com/url?sa=t&sourc...W6TAjQ&cad=rja

Gary
PS. have you read our answers on rim board insulation and procedures when installing rigid foam board/drywall?

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