Partial attic insulation
Hello all. Thank you for your time, I really appreciate it. Question, we have 2 bedrooms on the top floor of our house (more like a finished attic with sloped ceilings) and i want to move over some closets. the house is insulated with fiberglass batts between the 2×6 rafters. The roof vents looked to have been closed up for years. seeing as there is no ventilation running through currently would i be able to spray foam the underside of the roof deck only where it is accessible in the closet areas and patch back in? i am only able to do one room at a time so there is a possibility that it will be a partial hot roof for awhile. we are also in need of a re roof which i will be insulating from on top of the roof deck as ceilings aren’t so high inside. what type of problems would i be looking at to partially spray foam? thank you very much!
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Hey Jack,
This is an interesting question, and I'm not sure I can answer it confidently.
As you know, closed cell spray foam under a roof deck is one way to create an unvented roof assembly. Of course you need to be able to hit appropriate R-values for your Climate Zone to make it work and I can't say whether it is a good idea to add spray foam here-and-there. Another option would be to add exterior rigid foam insulation when you reroof. Perhaps a GBA user with experience in a similar situation will see this question soon. If not, I'll circle back and see if I can find an expert to answer it. In the meantime, here's an article that may be helpful:
https://www.greenbuildingadvisor.com/article/how-to-build-an-insulated-cathedral-ceiling
Thank you very much i read through that a few times and that would be my eventual goal when the time and budget allows. also exterior insulation is the plan when we do reroof but that is a few months out.