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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Here’s links to a collection of some of our other blog posts about PLUMBING DRAINS AND TRAPS:

• Why can't a sanitary tee be used for a horizontal-to-horizontal drain pipe connection? 

• Is a washing machine drain hose required to be secured at the standpipe?

• Why is it a problem when a trap under a sink is installed backwards? 

• What are the code requirements for plumbing vent terminations?

• What are the code requirements for layout of drain piping under sinks?

• What are the building code requirements for gray water reuse in Florida?

• What causes a gurgling sound when a bathtub or sink drains? 

• What is the difference between a vent stack and a stack vent? 

• Why is garbage disposal not allowed at a combination waste and vent (CW&V) under a sink?

• What is a building trap?  

• What is an indirect waste receptor? 

• What is the difference between water pipe and sewage (waste) pipe? 

• How can I tell if a house is connected to a septic tank system or sewer?

• Should I seal the washing machine drain hose to the standpipe?

 • Why is the European-style bottle trap not approved by the plumbing codes in the U.S.? 

• What is an auto vent, air admittance valve, or check vent?

• Can I make a trap under the sink from straight pipe and 90º elbows?  

• If all the plumbing drains have water in them and you can still smell sewer gas, what's causing the problem?  

• Why is there a flexible accordion pipe under the sink? 

• How do I get rid of the sewer gas smell in my house?  

• What are the pipes on my roof? 

• What is a "cross connection" in a home's plumbing system?

• What is an "S-Trap" under my sink? Why is it a problem? 

• What is a P-trap?

• What is the difference between gray water and black water in the plumbing code? 

• Is a sink required to have a drain stopper? 

• Can a laundry sink drain be installed without a trap under it? 

• What is a drum trap at a plumbing drain?

• Can a dishwasher drain hose be connected after the sink trap (to the trap arm)? 

• How far away from the sink can I install a dishwasher? 

• What is a double trap in plumbing? 

• Can two sinks share a trap? 

• Does a home inspector check sewer lines underground? 

• What types of plumbing traps are illegal by code? 

• What is bell trap at a plumbing drain?

   Visit our PLUMBING DRAINS AND TRAPS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.