Exhaust Into Attic

No you cannot vent your bathroom exhaust fan into the attic.

Exhaust into attic.

Because what happens is when the insulation gets moist from all that moisture that s being dumped into the attic it completely cuts down on the r value of the insulation. So you do need to get that vented outside whether it s through the siding with one of those trap doors that sort of opens out every time you ve got it on or through. The best exhaust fan venting is through smooth rigid ducts with taped joints and screwed to a special vent hood. And many building codes require discharging exhaust to the building s exterior so it s just a good rule of thumb.

You should never exhaust the bathroom fan directly into the attic. Dumping bathroom exhaust into an attic or under roof space invites costly mold contamination frost under the roof in freezing climates moisture damage to roof sheathing possibly even plywood delamination or rot roof failures and shorter roof shingle life. You can find 4 in. Venting into the attic sends excess moisture to that space which can cause mold and other problems.

Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents. Although this isn t always possible in attic crawl spaces you should always insulate the duct to prevent condensation problems. We ve also seen homeowners have to replace all their roof decking because it became rotted from the excess moisture. It may also violate a shingle warranty.