I’ve got a shop I’m building and I’m in the insulation process. Due to the order minimums I have enough R23 Rockwool comfort batts left over from the walls to do almost all of the attic. It’s vented and built with 2×4 trusses.
Since the bottom cord is only 3.5” tall and my insulation batts are 5.5 tall, I’ll have 2” proud of insulation sticking up.
My plan was to add rolled fiberglass insulation on top of the Rockwool to achieve a R53.
Would there be an issue of compression since the fiberglass rolls will only be supported by the Rockwool batts? Is it really going to compromise the R value?
Replies
Will your wall studs have the same spacing as the roof trusses?
One way to go would be to lay the fiberglass at right angles to the rock wool layer below, (cutting to length where the truss webs are)
If you are ambitious you can cut some of the rock wool to sit on the upper surface of the bottom web of each truss to take up the 1.5 by 2 inch space.
R 30 unfaced fiberglass will weigh about 8 ounces per square foot. Not enough to seriously compress the rockwool below (it would seem to me)
Yep the trusses line up with the wall studs exactly. And the trusses have an energy heal of about 12” total before I install baffles.
If I have extra I’ll fill in on top of the bottom cords but i will definitely go over the top will R30 rolls.
I’ve got 1” of exterior foam insulation as well. So hopefully it’s both warm in the winter and cool in the summer with the mini split.
Blow in cellulose or fiberglass on top of the rock wool. It will better fill in gaps caused by the trusses.