New window install; full depth foam or foam + fiberglass?
BrunoF
| Posted in General Questions on
When my windows were installed, the crew installed canned foam against the flange, between the window frame and RO only to a depth of 1-2”, I have 2×6 studs and need to either fill the rest of the space with foam or with fiberglass.
is there a best practice with this or will either one suffice?
thx!
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Replies
2 inches of foam is sufficient if done correctly. It's all about the air sealing. Personally, I'd fill the rest with Rockwool.
This really depends on the wall construction if you even need that gap filled any further. If you have some newer/nonstandard type of framing like Zip-R, double stud, exterior foam, etc then it's a whole other sequence and wholly dependent on the specifics of your wall assembly. Assuming that by "2x6 wall" you mean a standard framed wall with: drywall, 2x6, plywood, WRB, window flange, trim/siding; then an inch or two of canned foam will be ok since the window frame is probably only a couple inches deep.
Before the jambs and trim go on I typically air seal around the window frame - wall gap with backer rod and a fairly flexible caulk like Big Stretch. This allows for a long lasting and flexible air seal.
Any gap between the extension jamb and framing is left unfilled due to the way I trim out the windows. I'm guessing this is the gap that you're seeing? Stuffing fiberglass into that gap isn't going to do much, it'll be more than nothing, but it won't stop air movement and stuffed fiberglass loses a lot of R value from compression so nobody really does it anymore. On a modern construction house it's not much of an air path typically, but on some older homes it can be a real source of drafts. Think of those big old spaces for window sash weights that had board sheathing to the exterior! That size of gap, a few inches wide and full wall depth would be worth air sealing and insulating, but that doesn't sound like what you're looking at here.
Thx folks. Just to confirm, yes you are correct with your wall construction assumptions. fiber cement siding, drainable housewrap, OSB (taped and caulked), flanged Marvin casements, R21 fiberglass and drywall.
It sounds like I don't really need to mess with the remaining depth and can just let the drywall go up next week.
Thanks,