I’m doing a little renovation in SE PA (4a/5a) and have modified an exterior wall that is old foil-faced 1/2″ polyiso over plywood. I had had a discussion with my carpenter that I wanted to replace the sheathing in this whole area with Zip but when I wasn’t around he went ahead and installed this (large, heavy) slider onto the existing (1990s?, beat-up) polyiso.

We’re just beginning the reno and I don’t think this is the hill to die on but I’m not happy about the amount of leakage in this wall assembly. At the moment I’m wondering:

• Given that the interior of these walls are gutted out – can I use gaps and cracks spray foam to seal things up a bit from the inside?

• Is this old foam board usable as it is or should I tear it off and replace with new stuff with an intact foil face, and tape the plywall seams while I’m at it?

I was thinking about trying to patch it up with HVAC foil tape but it’s like swiss cheese, so that feels pretty futile. I like the idea of re-using this material as the greener option but it’s pretty beat up. I’ve seen others in this forum mention repairing foam board with spray foam but I’m not totally sure how that would work.

(Ignore the big door-shaped panel of exposed plywood -that will be a window on the upper part when it arrives, and below will get new foam board.)