I am adding an addition to a house that will have a metal roof. Our typical install is osb decking then 30lb felt, then 2×4 runners 24″ on center to attach the metal to.
The roof is cathedral with 2×8 rafters and batt insulation with vent baffles.
I’m considering putting 3/4″ or more foam on on top of the felt between the 2×4 runners for extra insulation: at least for the part below the flat ceilng. The room is 23 x 30 and 6/12 pitch with a structural ridge and 2×6 walls. The ridge will be vented.
Any opinions? Do ya think it will be worth the expense. Any better Ideas?
dug
Replies
So what are you gaining on the R value?
I don't know if it's gonna be worth it w/ just 3/4" foam board.
Will you have a problem w/ condensation from the metal?
Dave
Edited 7/15/2008 11:16 pm by DaveMason2
You need another layer of plywood in there if you want
to avoid the sound of rain falling.
The way they do it here is plywood, felt, then layer of foam,
with seams taped, then 1x2 strapping for air space,
plywood, then metal.
Keep the ridge vent for the metal only. Seal up and tape all the foam seams, using polyiso with foil side up. 2x4 pulins, then metal roof.
Throw away all your baffles and batts.
Spray cells, or better yet CC foam, to the bottom of the roof sheathing.
Good to go.
My .02¢
Ray