Why am I supposed to seal ventilation baffles?
One reason for venting a roof (in addition to keeping the sheathing cold) is to release moisture from the attic. Given that (and assuming it is a given) I’m a bit unclear on the benefit of air-sealing ventilation baffles, particularly in a cathedral ceiling application where the baffles are continuous from soffit to ridge.
If I’m trying to ventilate the insulation space, why would I intentionally create an air-tight barrier between it and the ventilation channel? Haven’t I just built an unvented roof? I don’t think I’ve so much eliminated potential moisture problems in the attic as I’ve just moved them from the bottom surface of the sheathing to the bottom surface of the baffle.
I understand the stated reasons for sealing baffles (keeping warm, moist indoor air from reaching the sheathing and reducing wind-washing) but I would think the intent would be to control, rather than eliminate, ventilation. I also understand that much of this is moot if the ceiling plane is properly air-sealed — but if I’m going to go through the trouble of venting, I’d like to make sure I’ve got it right.
Can anyone help me out?