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  • Writer's pictureTodd Engle


A common vent is one vent that serves more than one fixture, functioning as an individual vent for each fixture. Wet venting is venting single or double bathroom groups or combinations thereof, where one vent pipe may serve all the fixtures connected to the wet vent. Waste-stack venting is venting individual fixtures through a drainage stack, and the over-sized stack functions as the vent. Circuit venting is venting up to eight fixtures with a single vent pipe. A combination drain-and-vent system is restricted to floor drains, sinks and lavatories, and relies on the over-sized drain pipe. Island-fixture venting has a vent installed below the flood-level rim of the fixture before rising to connect to another vent.

Here are some important terms and definitions related to different types of vents:

  • The stack is a general term used to refer to any main vertical drain, waste, and vent (DWV) line that extends through at least one story of a building.

  • The waste pipe or waste stack conveys only liquid sewage not containing fecal material. Waste pipes do not convey human fecal matter.

  • DWV is the abbreviation for drain (or soil), waste, and vent piping used commonly in houses. The pipe will often be labeled "DWV."

  • The soil stack or soil pipe conveys sewage containing fecal material. In the plumbing trade, “soil pipe” is a common name for cast-iron drainage pipe. The term, however, is not specific to cast-iron pipe and refers to any DWV drainpipe that conveys the discharge of water closets, urinals, or any other fixture that receives human waste.

  • The stack vent is provided for the waste stack. The stack vent is the extension of a soil or waste stack above the highest horizontal drain that is connected to the stack. This is the main commonly-observed pipe that is observed penetrating the sloped roof surface, and it may also be visible in the unfinished attic space. Generally, a stack vent extends to the open air and can serve as the main vent to which branch vents connect.

  • The vent stack is the vertical vent pipe installed primarily for providing air circulation to and from any part of the drainage system, which is the piping in a home that carries away sewage or other liquid waste.

  • A local vent stack is a vertical pipe into which other pipe connections are made from the fixture side of traps. Vapor or foul air is removed from the fixture through the local vent stack.

  • The building drain is the lowest pipe of a drainage system into which drains the soil, waste, and other drainage pipes from inside, and it extends at least 30 inches beyond the exterior building walls. This is extended into the building sewer.

  • The building sewer is the piping that extends from the end of the building drain and connects to the public sewer, private sewer, or individual sewage system.

This is an inspection image of a stack vent. The functions of a stack vent and a vent stack are similar, but the main difference is that the stack vent is a direct extension that must reach outside air.

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