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Venting Exhaust Fans Through the Roof

Vent your bath and kitchen exhaust fans through the roof through a special roof hood. Venting through a roof vent or exhausting them in the attic could cause moisture problems and rot.

By the DIY experts of The Family Handyman Magazine

Venting Exhaust Fans Through the Roof

Vent your bath and kitchen exhaust fans through the roof through a special roof hood. Venting through a roof vent or exhausting them in the attic could cause moisture problems and rot.

Vent exhaust fans through a roof hood

If you’re tempted to vent your exhaust fan through an existing roof vent, or even vent it into the attic, don’t do it. First, you’ll partially block your roof vent with the piping, reducing the flow of cooling air through your attic. Second, during cold winters, you’ll be blowing warm, moist air onto a cold surface (the roof vent and roof plywood). The water will condense and drip into the insulation below and perhaps into the house. Special bathroom fan roof vents with an internal damper that opens only when the fan is blowing will send moist air outdoors and keep cold air out of the house.

Placing the vent

Placing the vent

Sealing the vent

Sealing the vent

Installing a Vent Hood on the Roof

Start in the attic and drill a hole through the roof in the desired vent location. Try to keep it close to the fan location. Leave the drill bit sticking through the roof so you can find the hole. From up on the roof, use a jigsaw or reciprocating saw to cut a 4-in. round hole. Next, measure out a square slightly larger than the protruding part of the vent. Remove the asphalt shingles with a hook blade fitted into a utility knife. Gently pry up the shingles around the hole, making room for the vent to slide under the first course. Apply a bead of asphalt roof cement on the bottom of the vent. Slide the vent under the shingles so they cover the top half of the vent flange. The lower half of the flange sits on top of the shingles. Nail the lower corners with roofing nails and tar the heads.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

    • Hammer
    • Caulk gun
    • Corded drill
    • Jigsaw
    • Pry bar

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

    • Roof-mounted exhaust vent
    • Asphalt roof cement
    • Roofing nails
    • 4-in. rigid or flexible duct with insulation

Comments from DIY Community Members

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January 17, 11:01 AM [GMT -5]

I have a question about who's responsible to pay for the damages in the attic by "improper installed" 2 bathroom shower exhaust fans. They were installed by previous owner that had no clue to what happened and said that they had no part of it. I had the Home Inspection came in and in his report said that it was a limited crawling space which not able to see everything in the attic last June before I moved in. Now, it's winter. All the molds, leaking thru the ceiling and both of bathrooms (I only use 1 bathroom shower). I understand why it's causing all that now, not during summer. I found out by HSA Home Warranty constructors said that the vent pipe was wrapped around in black tape which is now is torn apart and other is missing. The vent pipe was clipped onto something in the ceiling of the attic, not thru the roof. The previous owner had the roof repair and covered 2 holes were designed for the vent pipes thru the roof. There is black mold of yellow old installation under fresh "newer" pink installation above the ceiling where the exhaust fans are, even in floating soak. Now, HSA Home Warranty said that they're not covered the "Secondary" damage and "improper install". I feel that Home Inspector overlooked it last June. If he would have told me about it, I would have it fixed right away to avoid the costs of the damages. I'm thinking since constructors were able to crawl all the way to there the exhausts, why wouldn't Home Inspector crawl thus far, too? Is it because due to Hazard Saftey? Well, I climbed up the ladder, not to crawl (I'm alittle bit of phobia with small space) but I could see from the ladder where all the pipes are torned apart, black tapes, etc. My dad and my husband crawled there, as well. That's my biggest questions...

January 31, 8:19 PM [GMT -5]

Usually they vent out the side wall or the roof.There is a video here:

http://www.bathroomfanexperts.com/article.php/panasonic-fan-installation-video/?id=150

I would be careful to properly evaluate where the vent will exit so that you understand how you can properly seal the duct so water and such cannot get in. If you do this part wrong, you may end up with mold, water damage, and other horrid things.

January 30, 2:08 PM [GMT -5]

My bathroom is on the main floor and no exhaust fan. How can one be installed?

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