Cape Cod attic with no soffit vents - foam it shut or figure out venting first?

I went through this exact decision on my own cape a few years back and I walked away from the spray foam quotes, glad I did. Here's my thinking: with open cell foam sprayed blind behind drywall, you're banking everthing on the installer hitting every cavity perfectly from a shotgun position through a small access hole. Foam shrinks as it cures, it pulls away from rafters in spots, and you will never know where the voids are untill you get staining on the ceiling or find frost on the sheathing one January morning. Warm humid air leaking through a gap hits cold roof boards and that's your condensation problem, just hidden where you can't see it. And sealing the gable vents kills the only drying path the roof assembly has. On a deck that spent 70 years breathing, that's asking for shingle and plywood trouble down the road.

We did the opposite of foam on our old cape and it made a real dent in the summer mugginess. Air sealed the flat ceiling and the top plates, dense-packed the knee walls, and left the gable vents alone. The AC stopped running nonstop that first July. Worth asking your guy if there's any way to get a vent channel on the underside of the slopes, even a thin one, since you've got no overhangs to feed it from. Might not be doable with short rafters, but it changes the whole conversation if it is. Also get whoever sprays to quote it with the drywall opened up so you can actually see what you're paying for before you commit.

One thing I'd ask both contractors is what happens at re-roof time. Foam glued to the underside of the deck means shingle swaps get messy and the roofer can't eyeball the plywood. My neighbor went unvented on his cape and regretted it when the roof needed replacing, the tear-off quote doubled. If your shingles are near the end of their life anyway, that's the moment to think about edge vents, since they go in with new roofing and don't need overhangs. Might change how you price the whole thing.

One thing neither contractor seems to have mentioned is which foam. It matters a lot on a roof like this. When I had closed cell sprayed on my garage roof, the inspector made us put an intumescent coating over it, 3 inches of foam and two passes of paint, because bare foam left exposed in the rafter bays is a fire issue. Open cell usally needs a vapor retarder coat on the inside face too. So if the cheap quote is spray-behind-drywall, the drywall is doing double duty as the code barrier, which is also exactly why you'll never verify coverage. Ask each guy to specify foam type, thickness, and how he plans to meet the barrier requirement. The answers will tell you who actually knows this assembly.

Following this one closely because my upstairs is the same setup, those little rooms with the slanted ceilings and a hatch behind the short walls. When the first guy said he could spray it all from the hatch I honestly pictured him reaching his arm into every gap and I can't picture how that works way up near the top of the slope where the space pinches shut. The second guy pulling the ceilings down sounds way more thorough but then I'm paying to rebuild every ceiling after. Does that second quote usually include hanging and finishing the new drywall too, or does that come later as a surprise?

Update: took the air sealing advice and caulked around the flat ceiling and the top plates behind the knee walls. The AC allready cycles way less, so that part feels solved. Still stuck on the sloped cavities though, and the re-roof tear-off point has me leaning away from foam. Anyone had fiberglass blown into those short rafter bays from the crawl side? Does it actually fill them without pulling the drywall down?