How to Vent a Bathroom Fan Through the Roof

  • By: Monica Shulz

On the highest part of the roof which is the roof ridge. Underneath these shingles, there’s a slot on the roof that runs the entire length. That’s called a ridge vent. It’s designed to let the hot air of the attic out pulling the cooler air from the soffit vents into the Attic. Unfortunately, it’s pulling more than just cool air into the attic.

Note: Under the overhang, there’s another kind of vent. This one right here is a vent from the bathroom fan and it should never be in a vented soffit since t’s causing the homeowners a lot of problems.

To vent a bath fan through the roof, you must first prepare a ductwork connecting the roof top to the bathroom. Then, drill a hole on the roof top. Over there, mount the vent hood using tri polymeric locking seal paste and put the nails to strengthen it.


First of all, if you notice noticed there is discoloration in the areas under the roof sheeting, that’s beginning of mold existence. What most people do is they have actually vented the bathroom fan outside but you vent it into a vented soffit. What happens is that, soffit pulls that warm moist air into the attic in the wintertime. It condenses onto the sheathing causing the sheathing to get wet, and causes mold to grow that’s as bad as venting the fan right into the Attic.

Therefore, I should take a more direct route to vent the fan right out through the roof.


First, we must set a mark of the vent hole. The best way is to mark with nails in the middle of the rafter bay. you need to take a nail, and you are going to drive it right through the roof sheathing through the roof shingles and it will stick up. Then, go to the outside and locate the nail.


Now, you can see where the nail came through the roof. This is where you’re going to drill our hole. We’re going to use this vent hood right here. It actually has a little door on the inside here that will close with gravity. The function is to keep the cold air from blowing back into the bathroom when the fan is off. It has a screen right there to keep the critters out.


Then, you should remove some roof shingles so you can drill a hole. First, you must measure the vent hood. In this case, it’s five and a half inches so what I’m going to do is I’m going to set my tape at two and three quarters out on one side, five and a half on the other side. That will center my vent hood right over the nail. After that, cut right across the area you want to put the vent hood on and remove that shingle.


Now, I got to break the seal of the shingle so I can slide the vent hood up under the shingles. Most of the time, when you place the vent hood between the shingles, it should fit good.


Now, I’m ready to drill a hole. I’m going to use a 4.25 inch hole saw for this.


If your original duct work is uninsulated, then change it to an insulated duct system. By doing that, it will lessen the chance of condensation forming in the winter when your attic is cold. You need to put sleeve into the pipe so you can connect the duct work to the roof.

The first thing you need to do is you need to crimp this so it will fit inside the pipe. By crimping this pipe, it actually makes it smaller so it’ll fit in the 4-inch pipe. As a result, it will fit inside this 4-inch pipe. To hold the two together, you are going to use a foil duct tape.

Finally, disconnect the old ductwork and connect with the insulated duct system we have.

Note: you need another person under the roof helping you to slide the ductwork up to the outside.


To hold the ductwork into its position, you are simply going to cut a couple of tabs on each side so you can nail it to the roof. Bend those little cuts over, slide the ductwork down just a little, hold it right there and get a nail.


Now, we’re ready for the vent hood. To start mounting the vent hood, apply a heavy bead of a tripolymeric locking seal. It seals it up really nice. However, you do not need to put the seal at the bottom side because if any condensation should form, it’ll run out under the hood.

Next, you are going to pick up the shingle, slide it right up in there, and push it down. Then, pick up the shingle again and drive the nail through the flange into the sheeting. Don’t forget to apply another bead of sealant right down the remaining shingles around.

Finally, put a couple of nails across the top of the vent hood. The vent hood is sealed. Now, when you turn on the bathroom fan, all that warm moist air will come out of the house and stay out of the house.

Is it OK To Vent Bathroom Fan Into Soffit?

While some people might apply the bathroom vent on the soffit, it is better to use the exhaust vent to circulate the air. This is because a bathroom vent in soffit usually suck the moist warm air into the attic.

How Much Does It Cost To Cent a Bathroom Fan Through The Roof?

The cost might vary. However, you can expect to pay around $200 for applying a new bathroom vent on the roof. This cost includes setting up the ductwork and applying new vent hood.

Do Bathroom Exhaust Fans Have To Be Vented Outside?

Yes, it does. Venting the bathroom fan to the attic will only cause you a problem. The moist warm air can be condensate and cause a mold later on.

Can I Vent 2 Bathroom Fans Together?

No, you can’t. However, it is possible to have one fan and one vent connecting two bathrooms.

How Do You Insulate a Bathroom Exhaust Duct?

It can be done by applying a spray foam around the duct. In this case, we also recommend to use fiberglass-lined HVAC duct.

Do I Need An Electrician To Install a Bathroom Exhaust Fan?

Most likely, you will need to hire plumber rather than electricians. However, if there is new wires and switch need to be installed, then it is necessary to opt for electrician help.


Now you understand how to vent a bathroom vent through the roof. We also have linked everything you need to do this process inside this article. Do you find difficulties to apply the insulated ductwork or mounting a vent hood? Go to This old house and find more useful tutorials like this. Or you can subscribe through their channel here.


the post discusses what you need to do to get the bathroom fan through the roof. Such as the ductwork,where to drill the hole and connecting the bathroom with the roof.