How Many Roof Louvers Do I Need

This Old House general contractor Tom Silva shows how to properly install a roof-mounted bath-fan vent. (See below for a shopping list and tools.)

SUBSCRIBE to This Old House:

Tom helped a homeowner with a bathroom fan that was venting moist air into his attic. The fan’s vent was installed on the underside of a roof soffit, causing moist air to get sucked up into the attic, which was leading to mold and mildew problems. To correct the situation, Tom moved the vent onto the roof, being careful to flash it properly so there would be no leaks.

Shopping List for How to Vent a Bath Fan Through the Roof:
– insulated duct
– vent hood
– sheet metal sleeve
– foil duct tape
– nylon zip ties
– tri-polymer sealant
– 1¼-inch roofing nails

Tools List for How to Vent a Bath Fan Through the Roof:
– hammer
– utility knife
– flat pry bar
– drill/driver fitted with 4¼-inch-diameter
– hole saw
– crimping tool
– aviation snips
– caulk gun

About Ask This Old House TV:
Homeowners have a virtual truckload of questions for us on smaller projects, and we’re ready to answer. Ask This Old House solves the steady stream of home improvement problems faced by our viewers—and we make house calls! Ask This Old House features some familiar faces from This Old House, including Kevin O’Connor, general contractor Tom Silva, plumbing and heating expert Richard Trethewey, and landscape contractor Roger Cook.

Looking for more step by step guidance on how to complete projects around the house? Join This Old House INSIDER to stream over 1,000 episodes commercial-free:

Plus, download our FREE app for full-episode streaming to your connected TV, phone or tablet:

Follow This Old House and Ask This Old House:


For more on This Old House and Ask This Old House, visit us at:

How to Vent a Bath Fan Through the Roof | This Old House