How to Install a Flat Roof Ventilation System

A home with a flat roof.
What You'll Need
Reciprocating saw
Roof tar
Metal flashing
Tar spreader

Installing a flat roof ventilation system can be a challenge. While a flat roof does not require any special techniques to install the vent system than a sloped roof, it does require a special kind of vent. The flat roof ventilation is a requirement for any home for removing gas build up in the drains of your home. The vent that is mostly used for flat roof ventilation is a mushroom type vent. This vent works well on a flat roof as it does not allow any water to enter into the system.

Step 1 - Locate Position for Flat Roof Ventilation

Before cutting the hole in the flat roof you will need to make sure that it is in the correct place. The best way to do this is to drill a screw into the roof through the attic. Make sure that the vent pipe does not go through a section of the roof where there is a joist. Use a drill and drive a screw through the attic ceiling to act as the center of the vent pipe.

Step 2 - Remove Roof Shingles

Once you know where the flat roof ventilation pipe will go you need to remove the shingles around the area. Make sure that you take care in removing the shingles so that you do not ruin other shingles.

Step 3 - Cut Hole in Flat Roof

With the screw acting as the center of the ventilation pipe you need to measure for the circumference of the ventilation pipe. Leave some room for expansion during the seasons. Using a reciprocating saw, cut out the hole in the roof.

Step 4 - Install Flashing for Vent

Lay down some roofing tar around the hole and set flashing on top of it. This will help to keep any water from leaking under the vent and into the attic. The flashing should go out from the vent hole approximately 4 inches. Nail the flashing into the roof sheathing with roofing nails.

Step 5 - Install Flat Roof Ventilation

Install the vent into the hole according to the manufacturer's instructions. Before you place the mushroom cap onto the ventilation you will need to set the shingles into place around the cover for a finished look.

Step 6 - Install Shingles

Many flat roofs do not have shingles like a regular sloped roof. The roof could have rolled rubber membrane, rocks, or asphalt tiles. Whichever material that your roof uses, replace them once the vent is installed.

Step 7 - Install Vent Covering

The mushroom vent has a top cover that keeps water from going into the drain system. Place the cover on top of the ventilation installation and secure with the supplied hardware.

Step 8 - Caulk Inside Area

Once the flat roof ventilation is secure on the top side of the roof, you should continue the weatherproofing with a bead of caulk around the pipe in the attic. Lay a bead of caulking around the area where the hole is for the pipe. Make sure it is a silicone-based caulk so that it will allow the pipe to expand during the different seasons.