How to Add Vent Pipe for Bathroom Plumbing


In all sewer-line installations, vent pipes are necessary attachments. They are made of ABS (Acrylonitrile Butadiene Styrene) plastic--as is the sewer line--and, though you should check with the local permit office, are generally 1 1/2 inches in diameter. Their purpose is to allow an exit for all waste gases to escape form the sewer line so they won't be dangerous. Vent pipes usually run up inside stud walls and through the roof, where the gas can then escape. Installation is fairly easy if you plot the route of the vent pipe before installing.

Things You'll Need

  • Vent pipe
  • Couplings
  • ABS glue
  • Hacksaw or power saw
  • Pencil
  • Sand paper or knife
  • Reciprocating saw
  • Roof shield and roof nails
  • Hammer
  • Shingles
  • Cut into the sewer line at the appropriate place and glue in a "reducing" coupling (sewer line generally has a 3-inch diameter and vent line generally a 1 1/2-inch diameter). Make sure the coupling is pointing up, or in the direction of the stud wall where you will insert the vertical sewer vent. If you are connecting into an existing vent line, make sure the coupling is pointed in the existing line's direction.

  • Work your way, cutting the new vent line and connecting couplings as needed, until you either meet the existing vent line or the stud wall where you will install the vertical vent line. Either connect to the existing vent line or drill holes in the stud frame (making sure all holes line up with each other) until you reach the roof.

  • Mark the inside of the roof where the vent pipe will go through, as an elliptical hole. Cut the hole out with a reciprocating saw, and push the vent pipe through. (Check with permit office to see how much vent should be sticking through the roof.)

  • Climb on the roof and place a roof shield down over the vent, slipping the shield's flat metal base under the shingles on the upside of the vent pipe. Lift those shingles and nail the shield to the roof (two or three nails will suffice) before resting the shingles down over the shield. Don't nail the shield below the vent-pipe hole, as this may cause leaking. Install new shingles on each side of the shield's vent-pipe hole.

Tips & Warnings

  • Each bathroom fixture usually requires a vent pipe, though some permit offices allow you to use one vent pipe for two or more fixtures by having one vent line go up to the roof and the other vent lines tapping into that line. Always check with your permit office/inspector to see what exactly is required in your area.
  • Check with the permit office to see how close the vent line must be attached to the sewer line from each fixture.
  • When gluing each coupling, hold it for at least 30 seconds for it to dry.
  • Remove all burrs with a knife or sand paper after cutting.
  • When drilling holes in the stud frame, make sure the holes are about 1/2 inch wider than the sewer line. This can be done by purchasing/renting heavy-duty plumber's bits made especially for drilling wider holes.
  • There are many types of couplings available: 30-, 45-, 60- and 90-degree couplings, as well as those designed to connect to existing vent lines. Before starting the job, check to see exactly which couplings you need. .
  • The roof shield is flat metal, roughly a foot square and with a rubber hole in the center for the vent pipe to go through.

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  • Photo Credit Perfect Plumbing image by Heydj from
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