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Insulating Existing walls add vapor barrier?

15 years ago

We have gutted our 1915 kitchen. We're located in an area of heavy rains in the winter. Should we put tar paper in each stud bay, against the interior of the siding before putting insulation in? There was mold on the interior of the siding(north facing),which we treated. In one spot I intend to use rigid insulation and another bat insulation. I want to keep moisture out of the bat insulation but worry that I might just be creating puddles of water at the bottom of each stud bay since the added tar paper is only stapled inside each stud bay.

Is there a better material to use than tar paper, that is a moisture barrier yet breathable, before putting the insulation in.

thanks so much, orchidca

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Comments (2)

mightyanvil
15 years ago
Is there no sheathing under the siding? Putting any form of asphalt saturated building felt against the inside of siding won't serve any purpose that I can think of. Once water is in the cavity it will cause damage. It might be possible to spray the inside with a liquid weather barrier but there would be no guarantee that it would work.
tryinbrian
15 years ago
I have to agree with mightyanvil, I can't think of any purpose to stapling building paper to the inside of the siding. If you have enough rain water infiltration to create "puddles" you have more serious problems. If it's an occasional errant leak onto the inside of the siding, I don't see that harming the fiberglass in any meaningful way. Now if you were putting in loose cellulous (which is more succeptible to moisture damage) you might have a point.

I would guess the mold you see is more likely from condensation forming on the siding from warm inside air hitting it. Make sure your inside air barrier (i.e., the drywall) is as tight as possible and perhaps leave an inch of airspace between the siding and your batts (if possible)

Another way to keep moist inside air from hitting you siding would be to cut styrofoam to be slightly smaller than each stud bay, then apply spray foam (e.g. great stuff) into the cracks all around to hold it in place. Even with this method, I would leave a little air space between the styrofoam and the siding to prevent any moisture from being trapped against the siding. And of course plug up any wire and pipe holes with caulk or great stuff as well.
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