Seal holes in the fan housing with caulk sealing putty or metal tape.
Attic insulation over bathroom fan.
If that moisture is released into your attic space it can cause significant damage to your insulation floors ceilings walls joists and roofing structure.
Seal around the exterior fan duct vent with caulk or a pre made exterior wall gasket.
I think you need to go into attic regardless as the fan housing probavly has brackets attached to the attic joists.
Install the fan then seal around the fan with caulk or canned spray foam.
You can buy a bags of cellulose from lowes fluff it up into a garbage bags and dump into attic after you are done on top of the area where you disturbed insulation.
Seal the exhaust duct to the fan box with approved metal tape or mastic.
Mar 8th 2018 2 12 pm.
It is very important that you exhaust your bathroom fan outside.
Or you rent a blower.
Insulate the bathroom exhaust vent fan ducts.
Work from the perimeter of the attic toward the door or hatch so that you don t trample all over the insulation you just put in.
Always cover the tops of the ceiling joists to make sure the insulation is deep enough to reach your target r value and to prevent thermal bridging the heat loss that occurs through the wood framing.
There are several options available for the ducting like flexible aluminum ducting.
If you see that your duct isn t insulated at all pick up duct insulation at the home center.
If bath fan ducting isn t properly insulated the moist air from your house will condense inside the duct.
Another approach could be an insulated hvac duct approach.
How well the insulation around the bath fan will work depends on the ducting greatly.
But some consider it somewhat flimsy and may not support the weight of insulation over any distance.
You may find that the insulation simply needs to be refastened.
Bathroom vent fan ductwork insulation.
In un conditioned space such as an attic where otherwise your fan duct will be exposed to cold attic air in winter use insulated solid metal ducting or insulated flex duct.