Insulating exhaust ductwork through roof
Socold
| Posted in General Questions on
Hello,
We are redoing ductwork in out attic for 2 exhaust fans, one for the bathroom and one for the kitchen range hood.
The ductwork for the range hood goes through the roof to a vent. My question is about the insulation of the duct, we are thinking 2 in foil backed insulation. Should this insulation touch the sheathing, or should it stop just below and be taped to the duct. I’m worried about condensation between the insulation and roof.
Also, should we caulk the connection from duct to roof?
We are in Canada, similar climate to Vermont
thanks!
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Replies
The insulation should include a vapour barrier (foil backed is good) and should be continuous from ceiling to roof, dont leave a gap below the sheathing. Where the duct connects to the roof vent should be connected with foil tape and caulking is not needed. The actual vent on the roof should be installed with positive laps and caulked with roofing tar. If you are new to this I would suggest getting a roofer to lend a hand, cheaper than dealing with leaks.
After years of building, we've abandoned roof venting, and run all vents out gables (ideally facing away from prevailing winds). Why chance more leaks?