Unfortunately, I have to run an 8 inch HVAC duct through an unconditioned kneewall attic in southern Ontario (climate zone 6). I am trying to decide between two options:
- Encapsulate duct with spray foam to a sufficient R-value (image 1)
- Bring the duct inside the conditioned space by framing and adding drywall around the duct. Then ensuring continuous fiberglass insulation around the building envelope (image 2)
I'm trying to understand if these are actually different. Isn't option 1 (spray foam) just the same except I avoid the work of framing/adding drywall?
If I spray foam, should I avoid spraying the duct where it is in contact with the conditioned space? And can I spray directly onto the duct surface, or do I need a vapour barrier?