How to Add a Vent to a New Plumbing System

The venting on a plumbing system is important for two reasons: It keeps the water present in the plumbing traps from being siphoned out by admitting air to the plumbing system, and it gives sewer gases a location to vent. Adding a vent to a new plumbing system can be a challenge, but it is required in most United States locations.

Things You'll Need

  • Keyhole saw
  • Jigsaw
  • Measuring tape
  • Plumb
  • PVC Vent stack pipe
  • PVC couplings
  • PVC primer
  • PVC glue
  • Table saw
  • Construction adhesive
  • Vent stack roof collar
  • Nails
  • Screws
  • Hammer
  • Roofing tar
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Instructions

    • 1

      Locate the end of the soil stack pipe. This is the main sewer pipe that ties all the plumbing fixtures into the main sewer drain. These are typically located in a central location on the house. Most modern stack pipes will be of PVC construction and about 4 inches in width.

    • 2

      Cut a hole in any ceilings as needed for the new vent stack to pass through. Use the existing soil stack as a guide and measure with a plumb or level where the new vent addition intersects with the ceiling. Use a keyhole saw or jigsaw to cut a hole in the ceiling drywall in a circle the width of the vent stack pipe. Sand down any rough edges.

    • 3

      Cut a hole in the roof, if needed. Continue measuring the vent stack upward through the ceiling to where it meets the roof. Mark a circle on the underside of the roof using a piece of the vent stack as your guide. Drive a nail or screw through the center of the mark. Go up to the roof and look for the screw or nail sticking up to mark the spot for the stack. Remove any roof tiles, shingles or other coverings in a 6-inch radius from the screw marker. Use a jigsaw to cut a hole in the underside of the roof, using the circle as a guide.

    • 4

      Measure and cut the vent stack pieces using a table saw. This will give you the straightest cut through the thick vent pipe. Fit the vent stack pieces together as you work to make sure they fit tightly. Place the stack pieces into the top of the soil stack, dry fitting them together to make sure your measurements are correct and the vent pipe is straight. Disassemble the stack pieces once you've checked the fit.

    • 5

      Starting at the top of the soil stack, apply primer, then glue, before fitting the pieces together. Work your way up through the ceiling, attic space and roof, as needed, priming and gluing the pieces together.

    • 6

      Apply construction cement to the bottom of a roof vent stack collar. Slip the collar over the stack until it is flush with the surrounding roof surface. Secure with nails around the perimeter of the collar. Seal the edges of the collar with roofing tar. Replace any roof shingles or tiles you removed from around the vent opening.

Tips & Warnings

  • Always consult local plumbing codes in your area prior to adding a vent stack to a new plumbing system.

  • Use caution when working on roofs.

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