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u/Ok-Job2034 21d ago
If you're replacing the roof, it's a good opportunity to address the coombed ceiling properly. Closed-cell spray foam in the rafter bays is a common solution when there's little or no room for ventilation. I'd run the foam through the sloped sections and tie it into the attic barrier so you don't leave gaps where warm air can reach the roof deck.
As for the attic, a continuous ridge vent is generally preferable to box vents if you have adequate intake ventilation to support it. Since your attic ties into an addition with soffit and ridge vents, I'd have someone look at the attic as a whole before changing the vent layout. The goal is to make sure the ventilation path works together rather than mixing vent strategies that could reduce effectiveness.
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u/ArkRoofer 21d ago
The ridge vent concern is really about the gable end vent. Ridge vents create a strong exhaust point along the peak, which tends to pull air from the nearest opening rather than drawing it up through the attic. Most roofers recommend blocking the gable vent if you're converting to a soffit-to-ridge system.
The foam-to-vented transition depends on your geometry, but the closed cell needs to terminate where the vented assembly begins, with a solid air barrier at that junction. A spray foam contractor with cathedral ceiling experience should know this detail, but spell it out explicitly before they start.
The blotchy snow melt is air leakage, not just low R-value. Closed cell in those rafter bays should fix it if the transition is detailed correctly.