How to install a bathroom fan roof vent

How To Install A Bathroom Fan Roof Vent (7 Step Guide)

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John

April 04, 2022

So, you’ve bought yourself a brand new bathroom exhaust fan and you want to set it up.

While you may have some idea about mounting this convenient appliance to the ceiling of your bathroom, there’s a good chance you’re having trouble understanding how to install a roof vent for it. After all, that is precisely the reason why you’ve ended up here. 

You’re definitely in the right place, though! In this guide, I will lead you through seven simple steps that will help you to effortlessly and correctly install a bathroom fan room vent. 

These are commonly installed by using either a reciprocating saw or a hole saw to cut out a hole in the roof. 

In this article, I will talk about: 

  • How to properly cut out a hole in the roof; 
  • How to make room for the vent body by cutting shingles; 
  • Why caulking the vent flange’s bottom portion is not something you want to do; 

…And more. Read on! 

The Introduction 

Rooftop vent

Sometimes, homeowners have no other choice but to install a bathroom exhaust fan so that it exhausts humid air through the roof. 

This typically happens when the bathroom is located on the second level of the house, or when it’s not really close to an exterior wall. Obviously, this makes installing the appliance so that it wents to a wall extremely difficult. 

Before proceeding to install a roof vent, it is very important that you read the user’s guide for your particular roof vent cap. 

The very first step in installing a roof vent is choosing the right location for it. After that, you will have to dry-fit the roof vent cap. You will have to remove – that is, cut away – some shingles for the main vent body. 

Once the dry-fitting part is completed, you will need to cut out a hole in the roof with your hole saw drill bit. After that, you’ll have to take a duct connector and connect the duct hose to the aforementioned roof vent cap. 

Before nailing the vent hood to your roof, it’s crucial that you properly caulk the underside of the roof vent flange. It’s also a good idea to check your local bathroom fan venting code.

Let’s take a much closer look at each of these steps: 

Step #1 – Choose the Right Location 

bathroom fan vented through the roof

As I said above, the very first step in installing a bathroom fan roof vent is choosing the correct spot for it on your roof. 

Obviously, the best location would be the one that is closest to your bathroom. You will want the roof vent to be as close to your bathroom as possible in order to decrease the number of bends and reduce the length of the duct. 

Another important thing to mention here is that a roof vent should never be too close to roof valleys, chimneys, and other roof vents. Keep it at least two feet away from these spots. 

After finding the right location, it’s a common practice to take a nail and hammer it through the truss bay or the center of the rafter from the attic. This will allow you to easily locate the spot where your vent will go once you’re on the roof – you will only have to find the nail sticking out of it. 

Step #2 – Cut the Top Shingles For the Vent Body 

Roof shingles

Before sawing or drilling a hole in the roof, you’ll have to make room for the square vent body, i.e. remove the top section of the shingles. 

For the roof vent body, you’ll have to remove the middle portion of the shingles. However, the vent body’s flange – usually made out of metal – has to go underneath the top course of the shingles. 

The thing you’ll need to do here is to measure both the depth and the width of the roof vent and then cut the top layer of the shingles with a utility knife. 

There is no need to cut the bottom layer of the shingles, though. That’s because the reciprocating saw or the hole saw can go through it quite easily. 

Step #3 – Dry-Fit the Roof Vent Hood 

Once you’re done with making room for the square-shaped vent body, you can proceed to the next step – dry-fitting the roof vent. 

To be able to put the metal flange underneath the top layer of the shingles – as I mentioned above – you will have to use a pry bar to break the seal of the surrounding bottom and top roof shingles. 

The parts of the metal flange that need to go underneath the shingles are its side and top portions. Its bottom portion, on the other hand, should be positioned above all shingles.

Step #4 – Cut the Roof Hole

Man drills a hole in a roof

Once you have managed to dry-fit your roof vent in a hassle-free manner, proceed to cut a round-shaped hole for the duct. 

Here, you will have two different options when it comes to tools for this job. As stated above, you can either use a reciprocating saw or a hole saw drill bit. 

A hole saw drill bit is a much better option for smaller roof holes (3” – 4”). However, if the hole you need to make has to be at least 6” in diameter, your best bet is to use a reciprocating saw. 

Step #5 – Install the Collar or the Duct Connector 

Even though its name is pretty self-explanatory, the duct connector is a (vital) part whose purpose is to connect the roof vent with the flexible duct hose. 

In most cases, one side of this small section of metal piping needs to be crimped with a pair of crimping pliers. As you can already guess, this makes it easier for the hose to slide inside the collar. 

Once you’ve done that, you will have to take some zip tie or foil tape and seal the hose to the duct connector. The only thing left to do now is to insert the other end of the connector into the hole on your roof. 

I would recommend getting someone to help you during this part of the job. To make the task easier, let this person hold the aforementioned collar while you are securing it to the roof. 

To be able to nail the collar to the roof, cut at least two tabs in it.

Step #6 – Caulk and Nail the Roof Vent 

Once the collar is adequately dry-fitted and secured to the roof, you can move on to mounting the roof vent over the duct connector. You will also have to install the side/upper flanges underneath the roof shingles. 

However, before inserting the roof vent, you will have to do some caulking. In other words, you’ll need to cover the underside of the vent flange with a bead of exterior caulking. 

One very important thing to point out here is that you shouldn’t caulk the bottom portion – only the side and upper flanges. To prevent condensation from taking place (and consequential water dripping issues), you will need to keep the bottom flange free of caulking. 

The next thing you’ll have to do is nail the roof vent. Once the cap is inserted, take a couple of rust-resistant roofing nails and hammer them into the roof vent’s flange. Do the same thing with the roof sheathing. 

Step #7 – Caulk the Shingle Edges 

Caulking gun

This is where we come to the final step – caulking the edges of the shingles. 

Once you have hammered the rust-resistant nails into the flange and the sheathing, it’s vital that you caulk the edges of the shingles situated on top of the side and upper flanges.

Check out this guide to oiling a bathroom exhaust fan as well.

The Takeaway 

While it’s true that setting up a bathroom exhaust fan in a way so that it vents to an exterior wall is a better option, sometimes that just isn’t possible – you have no other choice but to install the duct to the roof. 

As I mentioned above, you will probably need someone to help you with this job – to hold the duct while you’re securing the roof vent cap. You will also need a couple of tools, such as the reciprocating saw and the hole saw drill bit. 

If you’re not a DIY-savvy homeowner or if you don’t want to put yourself in danger by going to the roof, your best bet is to just hire a qualified roofer to do this job for you.

If you plan on installing a new unit, check out our pick for the best bathroom fan.

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