Half cathedral ceiling venting with spray foam attic
Hi experts,
Hoping to get some advice. I live in Massachusetts (climate zone 5A). Before we moved in to our current home four years ago, we converted the formerly vented attic to a conditioned space by applying open cell spray foam to the underside of the roof sheathing in the attic. We did this so that we could install a more efficient HVAC system that required a conditioned space.
We have a guest room with a cathedral ceiling. Half of the cathedral ceiling is within the attic space. In other words, from the attic, you can see the ceiling, and there is attic space, with the roof sheathing above it. The other half of the cathedral ceiling is not within the attic.
I am concerned that the half of the cathedral ceiling that is not within the attic (a) was not spray foamed because there was no way for the contractors to access the underside of the sheathing and (b) is no longer ventilated because — I am guessing — the former ridge vent is no longer open, because the spray foam would have filled the ridge vent in its entirety.
So a few questions. (1) How can I tell if the ridge vent is still open at least on the side of the cathedral ceiling that is not covered by attic? If it helps, for other reasons we may need to open up the Sheetrock in the guest room. Will we be able to see whether the ridge vent is open? (2) If the ridge vent is not open, what are our options? I imagine trying to open it up would be a bad idea because it could destroy the seal on the attic. Should we just open up all the Sheetrock in that room and spray foam the rest of the sheathing? One concern there is that I believe that our roofing contractor installed ice and water shield all the way on the exterior of the roof when we replaced the roof a few years ago. So if we added spray foam, would that create a dangerous vapor barrier sandwich? Does the answer depend on whether we use open cell or closed cell spray foam? Would a better solution be to fill the space with cellulose?
Many thanks for any and all advice.
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Replies
I'm having a hard time visualizing exactly what you're describing, but it sounds like your guest room has a catherdral ceiling in one part -- with the ceiling going from the eave to the ridge, and the other part of the room the attic bumps out into the room and obstructs part of the ridge side of the ceiling. A drawing would be a big help here.
If you have continuous rafters from the eave to the ridge entirely within the cathedral ceiling area, it is unlikely the spray foam would have gotten into those -- they should be the same as they were originally. If you have areas where the rafters run from the eave then into the conditioned attic before reaching the ridge, I would expect that the spray foam now blocks the top part of those rafter bays and they are no longer vented.
In the first case, you could check from the roof, just look into the ridge vent or peel some of it back to check that it's clear. There are various styles of ridge vents so you'll have to see what you can do with what you have. In the second case, with newly blocked rafter bays, the easiest solution is probably a vent on the roof in each bay just before the rafter bay gets to the obstructed area. This will "re-vent" those rafter bays and that part of the cathedral ceiling. You need one vent for each bay in this case.
If you are opening up the drywall in the obstructed bays, I would just convert that to an unvented assembly with more spray foam. If you have the option to vent it, you could put a baffle in too -- just make sure you have enough space left between the bottom of the baffle and the top of the drywall to fit at least code minimum levels of insulation in.
Bill
Thanks so much for the reply. Here’s a photo of the portion of the attic by the guest room. You can see that the right side of the guest room ceiling has attic above it, but the left side is not accessible from the attic. The ridge vent of the house was at the top of the photo, and appears sealed. Unless you think it is possible that there are ventilation baffles above the spray foam that are still somehow operational?
How would one add the vents you are describing within the rafters? Are they like soffit vents but for the middle of a roof? I was not aware that was a possibility!
If we went the spray foam route, would open cell spray foam be ok even though there is ice and water shield on the top side of the sheathing? Would filling the cavity with cellulose be a better solution?
It's possible the spray foam installers may have put in vent baffles to keep the ridge vent connected to the part of the roof they weren't foaming. I would certainly check that to be sure though. If the ridge vent is sealed, you can use a roof vent like this (there are different styles, this is just one example):
https://www.homedepot.com/p/Master-Flow-60-sq-in-NFA-Aluminum-Slant-Back-Roof-Louver-Static-Vent-in-Black-SSB960ABL/100041904
If you go with spray foam for the rest of that roof, I would use closed cell (safest), but open cell is probably OK too.
Bill
Thank you very much!