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Tuff R as a vapor barrier


knothandy's Avatar
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VA

01-11-11, 07:41 AM   #1  
Tuff R as a vapor barrier

Remodeling laundry room. 1975 Virginia house. The room has one exterior wall with the following wall assy (looking from the inside of the house outwards): drywall, kraft-face over batts, R-15 batts between 2x4 framing, 5/8" plywood sheathing, 1/2" rigid insulation, vinyl siding. I want to add 2" rigid insulation to the inside of the exterior wall to warm up the room a bit. Since it's a laundry / drying room moisture needs to be dealt with correctly... given that the 2" fiber board has a perm rating of 1.0 and kraft is 0.2 should I get rid of the kraft facing before I install the 2" board? Will it matter? Thoughts, thanks.

 
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01-11-11, 08:22 AM   #2  
You can't increase the R value in the 2x4 walls by compressing the existing insulation and adding 2" foam. Compressed insulation doesn't insulate. If the room opens or is vented into a living space, as it should be, there should be no problems with moisture. That is if everything is vented properly to the outside. You probably only have R13 in the walls. The new rockwool products sold at big orange and blue fit snugly, require no stapling and you cover it with a plastic vapor barrier to the inside, then your finish covering. I believe the 2x4 size is rated at R15.

 
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01-11-11, 08:51 AM   #3  
We meet again. I wasnt clear: I intend to pull off the existing drywall (6x8 ft), lay the fiber board over the studs, then re-hang some new drywall. I certainly do not intend to compress the FG. I'm sure it's R-15 because I replaced the original R-11 about 3 years ago (from the outside before hanging new vinyl siding). It is Certainteed friction fit batts. I was wondering if I should pull the kraft facing off the existing batts if I am going to put the 2" Tuff R over the studs. All of this is about moving the clothes drying racks into the small laundry room (5x5 sf) and rigging up drying racks to the walls. I will put in a bath fan that vents to the outside. Hope this all makes sense!

 
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01-11-11, 02:42 PM   #4  
I'm a little confused. You say you introduced this insulation from the outside. How did the kraft paper get on the inside and how was it fastened? The foam is a vapor barrier itself, so it won't hurt to have it against the kraft. How do you propose to install the sheetrock? 2" is a long way to screw sheetrock in and allow for any integrity in the install. You will have to use 3 1/2" screws to reach and grab the studs.
To a basic question. Why do you think this wall of all walls needs extra insulation, and will it be worth the cost and effort and space you will lose? Just curious.

 
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01-12-11, 06:34 AM   #5  
Current insulation is "friction fit" - just pushed between the studs - which is snugger than original, a very poor instalation: if batts were too narrow they just left the gap, too wide? they just forced it into the stud bay, and ALL of the old batts were installed against the house wiring - a lot of baseboard heater wire run through this house and it gets hot - every single batt had their kraft face burnt off! Anyway, I'm replacing the drywall anyway because I am removing a big in-wall heater, repairing two other poorly executed penatrations that leak air during the winter, AND I need some nailers behind the drywall in specific places to hold the new, very heavy drying racks for drying clothes - remember we dont use a clothes dryer and I want to move all of the drying back into the laundry room instead of the house always looking like the corner laundro-mate. Cheers (and thanks as always). PS - I did this elsewhere and, yes, 3-1/2" does the trick very nicely - just need to hit the studs square on.

 
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01-19-11, 09:28 AM   #6  
OK. Backing down from this one. I think if I just seal said wall that will be improvement enough and I wont have to bump out the whole interior wall. It is the dryer vent penetraiton that is leaking badly. Cheers.

 
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