I would like to add insulation to my attic. I currently have about 3 inches
of 40 year old rockwool insulation between the joists. I do not think there
is a vapor barrier anywhere in the attic. My plan was too leave the old
rockwool (or whatever it is) alone and roll out new bats of fiberglass
insulation perpendicular to the joists (covering the wood joists for maximum
effect). Should I get faced or unfaced insulation?
How do I add additional layers of attic insulation to a joist cavity
that is only half full?
If joist cavity is only half full and the recommended insulation level
in your area is R-38, fill the joist cavity flush with the top with the
appropriate thickness of fiber glass insulation. Then lay a second
layer of unfaced insulation perpendicular to the existing layer to give
a total of 12" (or an R-value of 38) in the joist cavity. Covering the
attic joists with the second layer will reduce heat loss through the
as it says at:
I highly recommend the cellulose. It's a little dusty going in, but it
does the job very well once it's there. Either way you go, make sure
your soffit vents aren't covered when you're done or you'll have
It's my understanding that kraft faced (or vapor barrier), that the VB
should be the closest to the heated area of the building. Since you have
insulation, you'd want non vapor barrier fiberglass.
Rolling across the joists sounds like exactly the way to go.
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