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Troubleshooting in Plumbing: How to Move a Vent Stack

Shane Grey

Although moving a vent stack calls for only basic plumbing skills, choosing where to move the pipe requires considerable planning. Plumbing codes outline the allowable sizes, lengths and locations of vent piping. If you plan to alter your plumbing vent system, you need to ensure that your renovation doesn't conflict with local regulations. Moving vent stacks usually requires a permit and inspection. When you apply for your permit, you can ask the building department for information regarding project-specific details.

Planning the Move

Vent piping typically runs from fixtures to the roof or a main stack.

Step 1

Determine the maximum allowable distance from the fixture that the vent services to the vent. This distance typically varies according to the diameter of the system's drainpipes. For example, 1 1/2 inch vents must branch from drainpipes within 6 feet of the fixture's trap. Choose a new vent position within the allowable distance.

Step 2

Determine if the new position exceeds the allowable length of the vent pipe. Allowable length varies from 30 to 100 feet or more depending on the diameter of the pipe. Consult a vent piping size and length chart from your local building authority to find the maximum length for your project's specific circumstances. Revise your selection to accommodate the requirements of local regulations.

Step 3

Check the proposed path of the new vent for obstructions. The ideal path requires as few holes as possible and does not intersect existing electrical and plumbing lines. While the pipe may pass through a wall's top plates and roof coverings, its path should not require notching or boring vertical holes through structural beams, joists or rafters. Arrange your new vent's path to minimize the impact on existing framing.

Installing Pipe

Step 1

Sever the existing vent stack from its branch fitting with a hacksaw or reciprocal saw; cut the pipe as near to the fitting as possible. Cut the pipe into sections to remove it from the wall or pull it out of the wall from the building's roof. Cut the remaining sides of the branch fitting from the drain lines, working as near to the edges of the fitting's openings as possible. Remove the fitting from the drain lines.

Step 2

Measure the distance of the gap created by removing the fitting. Use a chop saw to cut a piece of replacement pipe to this size. Smooth the cut ends of the drain lines and replacement pipe with a piece of emery cloth. Clean the pipe ends with a clean rag. Slip flexible couplings over both open ends of the existing drain line. Insert the replacement pipe into the gap in the drain line.

Step 3

Slide the couplings over the replacement pipe so that the couplings join the existing lines to the replacement pipe. Tighten the couplings' clamp screws with a screwdriver.

Step 4

Use a hacksaw or reciprocal saw to cut an opening for the new branch fitting at the desired location. The opening must accommodate the breadth of the replacement branch fitting and allow the fitting to slip over the existing drain lines as necessary.

Step 5

Smooth the open ends of the drain lines with emery cloth and wipe them with a clean rag. Dry-fit the replacement fitting into the opening. If you are using a street tee, slip a flexible coupling over the pipe that will accommodate the male side of the fitting. A standard street tee has two female openings and one male; this type of fitting eases installation where existing pipes cannot be bent to slip into a fitting's openings.

Step 6

Apply pipe cement to the inside of the fitting where it will connect to the existing drain lines and to the outside corresponding pipes. Slip the fitting onto the pipes, twist until its top opening faces up and hold in position for roughly 30 seconds. If you're using a coupling, slide the coupling over the street end of the fitting and tighten the coupling's clamps with a screwdriver.

Step 7

Cover the fitting's top opening with a rag. Run a plumb bob between the center of the fitting's top opening and the underside of the wall's top plate. Draw a mark on the underside of the plate to represent a plumb line between the fitting and plate's underside. Attach a hole saw to the power drill and drill through the mark to create a path for the new stack.

Step 8

Lay out a similar mark for the vent stack's protrusion through the roof. Use the hole saw to drill an access hole through the roof, removing roof coverings as necessary. Cut a length of pipe to run from the branch fitting to the roof. Note that most codes require vent pipes to protrude at least 1 to 2 feet above the roof's surface. Clean the pipe's end and fitting's remaining opening. Feed the vent pipe through the holes and join the pipe to the fitting with cement.