Attic Insulation Retrofit and Mold Mitigation
Hello, I’m hoping someone can offer some guidance here. In doing some recent air sealing work in my attic I came upon some blackish-gray mold in 3 stud bays on an exterior wall. I did a bit of investigating and it seems that the builder neglected the top plate in the wall below, just in these bays. It’s in a funny area, behind a closet and a nearby roof line above a cathedral ceiling below meets the wall in that general area. First, when I look down into the wall cavity by pulling the R19 batts back from the sheathing I can tell right away the the mold is not in the wall, just up above the wall insulation. I assume this is because I have warm moist air leaking up freely, hitting the cold sheathing thus giving the mold a place to thrive. Does this seem logical?
Once I have dealt with the mold I’m wondering how to best ensure I don’t see the black stuff creep back up the wall in the same area. I was thinking the easiest way I can address this problem is to build an air seal from above and tuck it down into the stud bay. I already have 2″ XPS boards and cans of spray foam on hand. My idea is that I’d recreate the missing top-plate using these materials much like way you air seal rim joists in the basement, just reorient the rigid to lay flat, seal the sides with spray foam then cover the top with regular fiberglass batts. This would be much easier than opening up the drywall below and fixing from the warm side of the wall assembly. Thoughts on this approach?
Lastly, I have loose fill cellulose in the attic now, maybe R50 in total if I can get everything raked back properly but no vapor barrier above the drywall. I’m pulling R30 faced batts out of my basement ceiling (not needed since I’m now heating the space and plan to finish it down the road). I’m wondering if I am better off peeling the craft paper off the batts and adding the insulation “over the top” vs retaining the vapor barrier and placing them down in joist bays, covering them with my left over loose fill after the fact. I won’t end up with enough to cover all of the attic with these, so I might just focus on adding insulation over the master. I’d rent the machine and add blown-in to level it out later. I’m concerned with creating another mold situation up there, hoping for some advice here as well.
I’m in Zone 5. The house was build in 2013. 3000 sq ft finished, 1300 unfinished in the basement. 2×6 walls, fairly tight construction as I had a blower door test done after the first year, 1650 CFM was the reading and I’ve only been buttoning things up as I go so I have to imagine the house is even more efficient now. Appreciate any feed back.
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