All about the plumbing vents

A proper plumbing system is about more than just pipes and drains — the plumbing vent is an important yet often overlooked component. Installed on the roof or in the attic, it allows air to circulate through the pipes, ensuring your drainage system works efficiently.

In this article, our roofers explain everything you need to know about the plumbing roof vent pipe: what it does, how to install it, how to unclog it, and what plumbing vent rules you need to follow.

What is a plumbing vent and what is it for?

A plumbing vent pipe is a vertical pipe that connects your home’s drainage system to the outside, typically through the roof. It allows air to enter the system, balancing pressure and helping wastewater drain smoothly.

Its role is twofold:

• Preventing siphon suction: Without proper plumbing ventilation, the water in your traps can be sucked out, letting sewer gases enter your home.
• Ensuring smooth drainage: It lets water flow freely without creating a vacuum in the pipes.

Without a good plumbing vent roof system, your sinks, toilets, and showers may drain poorly, make gurgling sounds, or emit foul odors.

Where is a plumbing vent installed?

In most cases, the plumbing roof vent pipe is installed directly on the roof. This setup is called a roof drain vent or plumbing vent roof. It’s also possible to place a vent in the attic, but this requires specific configurations — especially when using mechanical air admittance valves.

Attic plumbing vents: be cautious

This setup is only allowed with approved systems (e.g., air admittance valves).

• It must be accessible for maintenance.
• It cannot fully replace a roof drain vent in all situations.
• It’s strongly recommended to consult a professional to assess feasibility.

How to install a plumbing vent?

Installing a plumbing roof vent pipe, especially with elastomeric membranes or asphalt shingles, requires precision. Here’s a general overview of the steps involved:

Drill an opening through the roofing system

Start by identifying the exact location where the plumbing vent pipe will exit the roof, based on the plumbing layout. Drill a clean hole through the roof deck (usually plywood), being careful not to damage nearby joists or wires. The opening should match the pipe’s diameter — usually 2 to 3 inches.

Insert the vertical vent pipe and connect it to the indoor plumbing system

Feed an ABS or PVC plumbing vent pipe from inside the house upward, allowing it to extend at least 6 inches above the roofline, per plumbing vent rules. The pipe must be securely fixed and connected to the rest of the plumbing system. The installation should be straight to ensure optimal air circulation and avoid water buildup.

Ensure proper waterproofing around the pipe

Waterproofing is essential, as the plumbing vent penetrates the roof envelope. Poor sealing can lead to leaks and costly damage.

Follow these steps:

• Apply a base membrane around the opening: Use a self-adhesive waterproofing membrane that extends slightly up the pipe.
• Install a flashing or storm collar: A rubber or metal flashing fits snugly around the pipe, acting as a water barrier.
• Seal around the flashing: Apply high-quality sealant around the collar to create a strong bond and prevent wind- or capillary-driven leaks.

Cover the installation with a finishing membrane

Finally, integrate the vent into the roofing finish. On elastomeric roofs, weld the membrane around the vent. On shingle roofs, carefully cut and fit the shingles around the flashing. In both cases, the goal is to ensure a durable, code-compliant waterproof transition.

At Les Couvreurs DuRoToit, we routinely work with plumbers to ensure your plumbing roof vent is properly installed, sealed, and built to last — no matter the roof type.

How to clean a plumbing roof vent?

A blocked plumbing vent can cause foul smells, gurgling noises, or slow drainage. Here’s how to unclog it:

1. Access the vent from the roof (safely)

Use a stable ladder, non-slip footwear, and a safety harness if needed. Avoid working on icy or wet roofs. Call a professional if conditions are unsafe.

2. Inspect the opening

Locate the plumbing vent pipe — it looks like a small vertical pipe sticking out of the roof. Check for debris like leaves, nests, or snow. A flashlight can help.

3. Insert a garden hose or flexible rod to dislodge the clog

Use a garden hose or flexible rod (like a gutter cleaner or drain snake) to gently push through the obstruction.

4. Use a plumbing auger for tougher clogs

If resistance is strong, insert a manual or electric plumbing snake and rotate it until the blockage is broken up. Avoid forcing it to prevent damage.

5. Flush with clean water

Once cleared, pour water into the plumbing vent to confirm it flows freely. Reattach any protective mesh or cap.

Tip: If you’re uncomfortable working at height or the clog persists, call a pro. Improper handling can damage the roof or piping.

Maintenance and inspection of your plumbing roof vent

Since it’s exposed to weather, inspect your plumbing vent roof regularly:

• After winter, to check for ice blockage
• Before fall, to remove leaves or debris
• During a roof replacement, to assess the sealing condition

During your annual roof inspection with Duro-Toit, ask us to check your plumbing vent pipe as well.

Why hire a roofer to install a plumbing vent?

While the plumbing vent is part of the drainage system, it passes through the roof — a critical point for waterproofing. A poorly installed vent can cause leaks, mold, and costly repairs.

At Les Couvreurs Duro-Toit, we ensure your plumbing roof vent pipe is installed with expertise, durability, and compliance. Your roof stays watertight, and your plumbing ventilation system runs smoothly year-round.