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How many plumbing vents through the roof are required by code?
Monday, October 12, 2020
Only one vent is required by the International Residential Code (IRC P3114.7): “Within each plumbing system, not less than one stack vent or vent stack shall extend outdoors to the open air.” Other fixture locations can use an air admittance valve, island vent, or combination waste and vent to provide the air flow necessary for good drainage. See our blog posts Is an air admittance valve (AAV) legal by code? and What is a "combination waste and vent" in a plumbing system? and What is the difference between a vent stack and a stack vent? for more on this requirement.
Although a plumbing vent that terminates in exterior air usually runs through the roof, the IRC allows other options, as long as the termination is away from doors, operable windows, any soffit vents, and a minimum of ten feet above ground. For full details, go to What are the code requirements for plumbing vent terminations?
There are also two good reasons to have just a single vent through the roof. One is aesthetic. Multiple through-roof vents distract from the clean lines of a handsome roof. In fact, most builders locate the single roof vent on the back roof slope. And the other is practical: every penetation of a roof surface is a potential future leak. The less penetrations, the better.
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