A good plumbing system isn’t just about pipes and drains: the plumbing vent is an often-overlooked component.

In this article, our roofers explain everything you need to know about roof vents: what they’re for, how to install them, how to unblock them, and the standards to follow.

WHAT IS A PLUMBING VENT AND WHAT IS IT USED FOR?

Its role is twofold:

Prevent drains from draining : Without a vent, water in your drains can be sucked back in, allowing bad odors to rise into the house.

Without a good roof vent, your sinks, toilets, and showers may not drain properly, make gurgling noises, or give off unpleasant odors.

WHERE IS A PLUMBING VENT INSTALLED?

 It is also possible to install a vent in the attic, but this configuration must meet specific standards, especially if a mechanical vent (with a flap) is used.

The first step is to locate the exact location where the vent pipe should exit, according to the plan drawn up by the plumber. Once the location is located, a clean, neat hole is drilled through the roof deck (the plywood ), making sure not to damage neighboring components such as joists or electrical conduits. The opening must be adjusted to the diameter of the pipe, generally 2 to 3 inches.

Insert the vent pipe vertically, connecting it to the interior exhaust network

The ABS or PVC vent pipe is then inserted from the inside out, extending about 6 inches or more above the roof, depending on the applicable standards. This pipe must be securely fastened and connected to the rest of the plumbing system inside the building. The installation must be perfectly straight to allow good air circulation and prevent water accumulation.

Apply a base membrane around the opening.

Start by applying a self-adhesive membrane (often called a waterproofing or base membrane) to the roof surface around the opening. This membrane should extend slightly over the pipe to create a barrier against water.

Install a flashing or weather collar

It acts as a protective dome, preventing water from seeping under the membrane.

Apply a sealant around the collar

A quality sealant is applied around the collar and on the junctions to ensure perfect adhesion to the surrounding materials. This prevents any water infiltration by capillary action or strong winds.

Cover everything with a finishing membrane

The final step is to complete the roof covering by covering the entire structure with the cap sheet. On an elastomeric membrane roof, the membrane is welded around the collar to perfectly integrate the vent into the waterproofing system. On a shingle roof, the shingles are cut around the collar and carefully secured to prevent leaks.