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

Do you want to learn how to install a bathroom fan roof vent?

Bathroom roof vents are typically installed using either a hole saw drill bit or reciprocating saws to cut out the roof hole.

In this guide, I will go over...

  • How to center and cut out the roof hole
  • Why you shouldn't caulk the bottom portion of the vent flange
  • And cutting the shingles for the vent body

Let's get started with this guide!

how to install a bathroom fan roof vent (3)

How To Install Bath Exhaust Fan Roof Vents?

Sometimes the best place to vent a bathroom fan is the roof. The bathroom is likely on a second level or far away from an exterior wall which may make it difficult to vent to a wall. Before installing any roof vent, I recommend looking up the manufacturer's instructions for that particular roof vent cap.

The first step to install a bathroom fan on the roof is to choose the location of the roof vent, and then you can proceed to dry fit roof vent cap—cutting away any shingles for the main vent body. Once it has been dry fitted, you can use a hole saw drill bit to cut the roof hole. After cutting the roof hole, the duct hose will need to be connected to the roof vent cap using a duct connector.

It is important to caulk the underside of the roof vent flange prior to nailing the vent hood to the roof.

To read the details on each step, keep reading...

Read Also: How Much Electricity Do Bathroom Fans Use?

how to install a bathroom fan roof vent

Metal bathroom fan roof vent cap

1. Choose The Location

The first step is to choose the spot on your roof for your bathroom roof vent.

The best place is as close to the bathroom fan as possible in order to reduce the duct length and number of bends. It is also important to make sure that the roof vent is at least two feet away from any other roof vents, chimneys, or roof valleys.

Once you have determined the location, it is a general practice to hammer a nail through the center of the rafter or truss bay from the attic. When you are on the roof, you can easily locate the nail that you hammered through to know the exact center of the roof vent.

Read Also: What Are The Best Bathroom Window Exhaust Fans?

2. Remove Top Shingles For Square Vent Body

Before you drill or saw the roof hole, you will need to remove at least a top section of the roof shingles for the square vent body.

The surrounding metal flange will go underneath the top course of asphalt shingles, but you will need to cut out the middle portion of the shingles for the roof vent body. All you have to do is measure the width and depth of the roof vent, and use a utility knife to cut the top layer of shingles.

The bottom layer doesn't need to be cut because the hole saw or reciprocating saw will go through it.

how to install a bathroom fan roof vent

3. Dry Fit Roof Vent Hood

After you have cut out the top shingle layer for the main vent body, you should dry fit the roof vent. You will have to break the seal of the surrounding top and bottom shingles using a prybar so that the metal flange can go underneath the top layer.

Only the top and side portion of the metal flange should go underneath the shingles. The bottom portion of the flange should be above all shingles.

Read Also: How To Fix A Noisy Bathroom Fan?

4. Cut The Roof Hole

If the roof vent has been properly dry fitted without issues, then you can move to cutting the round roof hole for the duct.

There are two options for cutting the roof hole, you can either use a hole saw drill bit or a reciprocating saw.

For larger holes such as 6-inches, a reciprocating saw may be easier than using a hole saw drill bit. But for smaller holes like 3" or 4", a hole saw drill bit may be preferable.

Read Also: What Are The Best Ventless Bathroom Fans?

5. Install The Duct Connector Or Collar

A duct connector is a small section of metal piping that connects the flexible duct hose to the roof vent.

At least one side of the duct collar is usually crimped which gives some space for the duct hose to easily slide into the collar. Once the duct hose is sealed to the duct connector with foil tape (or zip tie), the other end of the duct connector can be inserted into the roof hole.

Duct connector

You will likely need a helper who can hold the duct collar through the roof hole while you secure it to the roof. When you are on the roof, you should cut at least two tabs in the collar so you can nail it to the roof.

6. Caulk & Nail The Roof Vent

Once the collar is secured to the roof and it has been properly dry fitted, you can install the roof vent over the duct connector (and the upper/side flanges underneath the shingles).

But before you insert the roof vent, it is important to put a bead of exterior caulking on the underside of the vent flange. Only put caulking on the upper and side flanges, do not caulk the bottom portion. You want the bottom flange to be free of caulking so any condensation or water will drip out.

Once you have inserted the roof vent cap, you should hammer a few corrosion resistant roofing nails into the flange of the roof vent as well as the roof sheathing. 

Read Also: How To Size A Bathroom Exhaust Fan?

7. Caulk the Shingle Edges

After you have nailed the roof vent, it is important to put a bead of caulking along the edges of the shingles that are on top of the upper and side flanges.

Professional Roofer Installation Is Recommended For Most Homeowners

Even though venting a bathroom fan to an exterior wall is preferable, sometimes you have no option but installing the duct to the roof.

Having a helper will probably be required to at least hold the duct and collar in place while someone secures the roof vent cap. A hole saw drill bit and reciprocating saw will also be needed to cut the actual roof hole.

For most homeowners, I would recommend having a qualified roofer do this installation due to the obvious dangers of dealing with a roof, as well as the leak risks.

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