What Size Roof Vent Pipe Is Used In Bathroom?

It’s typically recommended that you go with a 2" PVC pipe for the vent. This is according to the uniform plumbing code (UPC). It may not be enough, depending on how many fixtures you are trying to run off the vent. You should check with local building code requirements to be on the safe side.

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Vent pipes shall be not less than 11/4 inches (32 mm) in diameter. Vents exceeding 40 feet (12 192 mm) in developed length shall be increased by one nominal pipe size for the entire developed length of the vent pipe.

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Vent pipes shall terminate not less than 6 inches above the roof, measured from the highest point where the vent intersects the roof. EXCEPTION: Where a roof is used for any purpose other than weather protection, vents shall extend at least 7 feet above the roof and shall be properly supported.

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Approved materials. Waste and vent pipes and fittings: Cast iron, galvanized steel, galvanized wrought iron, copper, brass, Schedule 40 ABS DWV and Schedule 40 PVC DWV are some commonly used approved materials.

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At least one of the primary 3, or 4-inch, drainage stacks should continue up and through the roof without changing the pipe size. Other smaller vent pipes from other fixtures can connect to this full-sized vent pipe. Avoid the temptation to eliminate a full-sized vent in your plumbing system.

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It also allows fresh air into the plumbing system to help water flow smoothly through the drain pipes. However, no water runs through the plumbing vent pipe. It is a vertical pipe attached to a drain line and runs through the roof of your home. The vent stack is the pipe leading to the main roof vent.

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When I was a plumber’s helper in the 1960s, we used a single 2-1/2-in. galvanized pipe to vent back-to-back kitchens and bathrooms. Nowadays, though, I see 3-in. vent pipe from every bathroom to the outside.


So a vent pipe the same diameter as the building sewer needs to connect from the drainage system, and extend through the roof, undiminished in size. One popular way to meet this requirement is by plumbing one toilet with a 3 or 4 inch vent.


Large-diameter (1 1/2 inch and larger) black plastic, cast-iron, and copper pipes are often used for the drain-waste-vent system. A 4-inch or larger plastic or cast-iron pipe usually serves the main soil stack, the waste and vent line that serves toilets and other bathroom fixtures.

How to Vent Plumbing Through the Roof

Frequently Asked Questions

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