How To Install A Shingle Roof Flange For An Electrical Service. Installing an electrical service mast through a shingled roof requires more than simply cutting a hole and sliding the mast into place. The roof flange needs to be installed and sealed properly to prevent water from getting underneath the shingles and into the building.
In this guide, we’ll walk through the process of installing and sealing a roof flange for an electrical service mast on a shingle roof.
Important: This method is specifically for asphalt shingle roofs. Metal roofs and other roofing materials require different flashing and sealing methods.
Positioning the Roof Flange
Start by cutting the required opening through the shingles and roof deck. In this example, the opening is approximately 4 inches in diameter.
The roof flange is made of metal and is angled to sit properly on the slope of the roof. Before installing the mast, the flange needs to be positioned so that the upper portion slides underneath the shingles above the opening.
Carefully slide the flange underneath the shingles and position it where it will sit. The flange may push up on the shingles, so some trimming may be required to allow it to sit flat.
A hook knife, utility knife, or another sharp cutting tool can be used to carefully trim the shingles around the flange. The goal is to create enough clearance for the flange to sit properly while maintaining the correct shingle overlap.
This work is best done on a warm day. Shingles are more flexible in warm weather, making them less likely to crack or break during installation. The roof should also be clean and free of debris before applying sealant.
Determine the Mast Height
Once the flange is positioned, temporarily slide the service mast through the opening.
The mast height needs to be set according to the applicable electrical code and the required point of attachment. In this example, the point of attachment is approximately 43 inches above the roof, which falls within the required range for the installation.
Once the correct height has been determined, remove the mast and cut it to the required length.
Apply Roof Sealant
With the mast removed, apply a continuous bead of suitable roof sealant around the underside of the roof flange.
In this installation, a product called Flex 9000 is used as the roof sealant. The bead should be applied around the entire outside perimeter of the flange.
Once the sealant has been applied, carefully slide the flange back underneath the shingles. Keep the flange angled as you push it into place, then lower it down and position it as square and level as possible.
The flange should sit tightly against the roof surface.
Seal Under the Shingle Edge
One of the most important parts of the installation is making sure water cannot back up underneath the flange.
Apply an additional bead of sealant underneath the lower edge of the shingles, working around both sides of the flange. The sealant should extend toward the outer edges to help prevent wind-driven rain from getting underneath the flashing.
After applying the sealant, press the flange down firmly and smooth the sealant as necessary.
Securing the Flange
Ideally, the flange should sit tightly against the roof. If part of the flange is sitting up off the roof, it may need to be temporarily held down while the sealant sets.
One option is to place a heavy object, such as a brick, on the flange and allow the sealant to cure. However, if the installation needs to be completed immediately, the flange can be temporarily secured with screws.
If screws are used, drill through the flange and into the roof. Then remove the screws and apply sealant into the holes and underneath the flange around the penetration points.
Reinstall the screws and tighten them down.
You should see some sealant squeeze out through the screw holes. This is a good indication that the holes have been properly sealed.
Once the screws are installed, apply additional sealant over the screw heads.
Apply a Final Bead Around the Flange
To finish sealing the roof flange, apply a small, neat bead of sealant around the outside perimeter.
Pay particular attention to the edges and corners. The goal is to create a continuous seal that prevents water and wind-driven rain from getting underneath the flange.
Take your time with this step. A neat bead of sealant not only looks better but also helps ensure that the entire perimeter is properly sealed.
Once the sealant has cured, the flange should be firmly secured and watertight.
Install the Service Mast and Rubber Gasket
With the roof flange properly sealed, slide the service mast down through the flange.
Before installing the service equipment on top of the mast, install the rubber roof gasket. This is important because the gasket may not be able to slide over the service equipment once it has been installed.
The rubber gasket fits tightly around the service mast. Push it down until it sits firmly against the metal roof flange.
The gasket should be pressed down tightly and positioned so that it covers the top portion of the roof flange completely. This creates an additional seal around the mast penetration.
Final Thoughts
A properly installed roof flange should direct water away from the penetration and prevent water from backing up underneath the shingles.
The key points are:
- Use a flange designed for a shingle roof.
- Carefully trim the shingles so the flange can sit properly.
- Apply a suitable roof sealant underneath the flange.
- Make sure the upper portion of the flange is installed underneath the shingles.
- Seal underneath the lower shingle edge to prevent water from backing up.
- Seal all screw penetrations.
- Apply a final bead around the flange.
- Install the rubber gasket tightly around the service mast.
When done correctly, the flange, sealant, and rubber gasket work together to provide a reliable seal around the electrical service mast.
Remember that this installation method is specifically for shingle roofs. Metal roofs and other roofing materials require different flashing and sealing techniques.
Always follow the applicable electrical and building codes for your area, and make sure the installation is completed by qualified personnel where required.
