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Vapor barrier, retarder, air sealing help?

user-7539645 | Posted in General Questions on

Hi All,

   GBA seems to be conflicting with local practice here in the Buffalo area, Zone 6.  I’m inclined to follow GBA advise, and want to insure I have it right before jumping all in.

I have a 1 1/2 story house about 35 years old recently purchased.
Had to replace the GAF roof with Owens-Corning and Ridge venting.
Attic #1 is about 800 sqf. and would like to replace the 2×6 cavities of double stuffed R19 fiber batts with R30 Mineral wool in non-covered places and R23 under attic floor areas.
According to GBA, it sounds as though:
1. I should not need a vapor barrier or membrane between attic floor drywall and insulation.
2. I need to air seal recessed lighting/penetrations, reroute bathroom exhaust fans to exterior, etc.

My questions are:
A. Would there be any real world benefit to caulking the 2×6 joists to the drywall before adding the new insulation? 

B. I have a new 30′ ridge vent in the attic section, however only about  25 x 3″ round metal intake vents. Previous exhaust venting was 3x 12″ x12″ static venting.  Would this be why it got excessively warm before the new roof, and still after?
Assuming I need to replace with 30′ continuous soffit.
Also the plywood underdeck and rafters were plenty dark with mold which I remediated with RM-66. Looks as bright as brand new, far better than straight bleach. Just using that Carborundom from HD to kill/seal mold roots.

C. I know I need baffles at the roof edge, and a dam below to prevent insulation blocking soffit.  My question is why do most baffle install videos show the baffle as several inches narrow on each side of the rafters?  Seems like that would reduce efficiency.  Could I get some foam board sheets of 4×8 and rip them to 24″ and run them across the bottom of the rafter before damming each cavity? 

D. I picked up a couple of rolls of radiant attic film barrier, and was hoping to use that to help reduce heat into the attic space. Could I use that as per C. above as part of the baffle?  Just read a comment somewhere that radiant barrier are close to useless in the NE, so unsure.

I’d greatly appreciate anyone giving me some schoolin’

GBA Prime

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