Air Sealed Plywood to Window Rough Opening
So I thought I had a plan but now I’m questioning myself a little on order of operations and the amount of tape. We are building double stud walls, euro flange-less windows, and taping the CDX with zip for the air barrier. WRB is Mento 3000. Target is for Passive House air tightness (because at this point I’m emotionally attached to that target).
So I’m looking for the best order of operations to water and air tight the opening. My thinking is:
1) Tack bevel cedar siding in place to create sloped sill.
2) zip tape entire RO with zip stretch in the corners and a wide 6 or 12″ tape to cover the whole cedar shim
3) Cover wall with Mento 3000 and cut for the window
4) Install window (setting it back from the plywood face by 2″)
5) Tape Mento to window exterior with Pro Clima tape
6) Foam and tape around window from the inside to create the air seal to the plywood buck
Anything you’d change the order on? Most of my favorite YouTubers are using zip, so the order of operations is slightly more straightforward. 475’s example uses Adhero so they are sealed to the plywood and the WRB all in one step.
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That sounds reasonable and similar to the way I've done it. You could save money on tape by running the WRB back into the opening and taping the corners with Tescon Vana or similar, then taping the WRB to the face of the window on the sides and top. Or depending on the window, the bottom as well.
For belt-and-suspenders, I like to include a back dam along with a sloped sill, but just the sloped sill should be enough in most cases.
I'm not sure I totally follow the running the WRB back into the opening. I opened the PGH book to look in there, page 113 has a pretty good detail too that is a bit different. But it doesn't have any sealing of the plywood face to the plywood buck.
On the back dam... We didn't think much about that before cutting the RO. We only have an inch of height. Maybe I could squeeze in 1/2" back dam. Slightly taller than the cedar strip.
If your air barrier is the taped CDX, the buck to sheathing transition should be taped like any other inside or outside corner transition.
Ok, after more thought, here is what I am going to plan for. I'm going to try and tape the sills this weekend. The framer was a bit worried taping to the face of the window might be visible past the trim. Any one have any good tricks? My trim plan is just 1x4 cedar to make an extension jam with the bottom piece sloped as a sill.