old house, where to put varpor barrier?
Hi, Long-time subscriber to FHB, new to the forum … finally having a chance to put all that great information and advice into practice.
Remodeling an older (1915) 2-story balloon-framed house on Long Island (AC in warm humid summer, cold winter) – stucco on T&G sheathing exterior, plaster interior. We’ve stripped most of the plaster from the 2nd floor exterior walls so we can insulate. With no blocking, most of the 1st floor bays can be accessed from the open 2nd floor. My contractor wants to blow-in “rock wool” to the 1st floor with fiberglass batts on the 2nd floor. I think I should be concerned about vapor condensation (GC doesn’t seem to be) … should I? and if so what is the best approach? Would applying a layer of closed-cell foam to the inside of the sheathing be enough?
Replies
Well, first think in terms of vapor retarder, not vapor barrier. You can use a "smart" VR like MemBrain under the new drywall, or just use a vapor retarding primer paint. Don't use poly inside, especially if you have air conditioning going on in the summer.
If you aren't gutting the first level, then you can't put a sheet of anything down there anyway, but the paint on the walls there may be all you need anyway.
Remember, movement of water vapor by diffusion is a relatively slow process. You move far more by convective transport (air leaks). You want to take the time to seal up the walls against air infiltration as best as you can.
Tell us what shape the outer skin is in. If you have rain getting in through cracks in stucco and around window openings (built in 1915, huh?), you need to think about insulation retaining water and not drying out quickly via air leakage.
Flashing thje inside face of the sheathing would be a good solution for that climate.
I'm puzzled about any insulation contractor who wants to use FG batts for anything tho, esp if he has the equipment to blow in cells, BIBs or rockwool
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We blew in Certainteed Insulsafe FG about 8 years ago in one wing of our original 1932 house (built the same way, balloon frame but with blocking) - then we took it all apart 2 years ago.
No moisture problems and good fill on the FG.
Jeff