Closed-cell spray foam cathedral ceiling — Drywall paint
user-6651407
| Posted in General Questions on
I might be overthinking this……should we be cautious of the type of paint used on the drywall, for a Closed Cell Unvented Cathedral Design? Will I be creating a double vapor barrier?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Maybe this would be helpful. https://buildingscience.com/documents/building-science-insights/bsi-092-doubling-down%E2%80%94how-come-double-vapor-barriers-work
My initial instinct was going to be to say that it would be fine (which is probably the case), but I guess it actually depends upon more the specifics.
Bridget,
The short answer is easy: Don't worry about the paint. You are describing a roof assembly with no inward drying potential whatsoever. Your closed-cell spray foam is already a vapor barrier. Adding paint isn't going to make your roof assembly any more or less likely to allow vapor to move through it.
I wonder about the details of your assembly, however. What's your climate zone? Did your insulation installer manage to provide you with the minimum R-value required by code? (Many insulation contractors who install closed-cell foam end up short-changing their customers -- because R-38 or R-49 of closed-cell spray foam is expensive.)
-- Martin Holladay
Climate Zone 5. We are still in the building process, so the insulation hasn't been sprayed yet. We are currently discussing how many inches to spray, as well as possibly doing flash and batt.
Bridget,
Here is a link to an article that discusses all of the different ways to insulate a cathedral ceiling: How to Build an Insulated Cathedral Ceiling.
-- Martin Holladay
Thank you, yes, I have read this article. If we decide flash and batt, will the fiberglass need to have the kraft paper face? This is where I get confused. I am worried I will be creating a double vapor barrier. Also, with the flash and batt, is paint on drywall a concern?
Bridget,
If you use the flash-and-batt approach, the use of kraft facing is not required. Ordinary unfaced batts work fine.
That said, kraft-faced batts would also work. Either way, don't worry.
Any type of paint is fine.
--Martin Holladay
Thank you so much, your help is always appreciated!