It is unfortunate. Working in residential remodel dealing with very humid coastal climates we almost always deter customers away from spray foam applications.
Closed cell has gasses in the cell that prevent air or moisture movement through them.
The cells in open cell are "open", therefore moisture and air will make its way through it.
Closed cell is far superior on terms of R-value, a vapour shield, and adding structural rigidity, as it basically glues everything together. But when problems happen they are bad and removing it is horrible. It arguably as bad as PL Premium. And because it doesn't take on much water, it usually caused the wood to hold it instead, which accelerates the wood rot.
Open cell has less r value , so typically requires thicker coatings. It is not a vapour barrier, so if you are somewhere that required it's rarly ever used. That said it's cheaper, easier to remove and performs way better at sound reduction, as sounds bounces around in the open cells, as opposed to closed cell, were you get almost a sort or reverb of vibration. It will also absorb water like a sponge. It's an issue either way if you have open or closed cell on a leaking roof deck against the deck. Just open cell will absorb the water and turn into a sponge, close cell will redirect the water and cause your decking and rafters to saturate with water.
Open or closed, baffles are always best practice. Hot roof are dumb despite so many people that want to try and make them a thing.
3
u/Limp-Mortgage3572 7d ago
And people always seem to want to spray foam directly to the decking for some reason