Running Pipes Through Walls and Floors

Running Pipes Through Walls and Floors

Once you've drawn a plan for new plumbing service, develop a strategy for running the pipes. In a new building or addition where the framing is exposed, this is easy. If you are remodeling, be prepared to make changes in the plan once you've removed the wall covering and flooring.

Replacing finished surfaces after plumbing (especially patching walls) usually takes several days. A large wall patch -- even replacing an entire wall -- takes only a little more time than a small patch, so open plenty of space for working.

Once you've opened the vent and drain lines, running the supplies -- which usually run alongside drain-waste-vent (DWV) lines -- will be relatively easy.


For a modest bathroom two or three days to cut into walls and flooring and run pipes through framing

Demolition tools, drill with various bits and hole saws, reciprocating saw, level, tools for installing pipe

Carpentry, knowledge of your home's structure, installing pipe

Have your plan approved by the local building department

Pipes, fittings, clamps, and assembly materials listed on your plan

Step 1

If you need to run a new stack, assess your framing. An installation with a toilet must have a 3-inch drain, which can be installed only if the stud wall is made of 2x6s or larger (2-inch pipe can be run through a 2x4 wall). Remove the wall surface up to the ceiling.

Step 2

Cut a hole with some wiggle room for the new pipe. For a 3-inch pipe, use a drill and reciprocating saw to cut a hole about 4-1/4 inches by 10 inches through both the bottom plate of the room you are working in and the top plate of the room below. Cut away a 10-inch by 2-foot section of flooring.

Step 3

Assemble the approved fittings onto the top of the drainpipe. Take special care that they face the right direction. The drainpipe should be longer than needed -- you can cut it to size from below later. Slip the pipe down through the hole.

Step 4

You may need to cut a hole in the wall of the room above or below to guide the vent pipe up or the drainpipe down. In the attic you may be able to run the vent over to tie into an existing vent. If not, drill a hole in the attic ceiling and have a roofer install a roof jack for the vent pipe.

Step 5

Anchor the drainpipe with straps. Cut a smaller opening in the ceiling for the vent pipe. For a 1-1/2-inch vent pipe, a 2-1/2-inch hole is sufficient. Guide the vent pipe up through the hole and into the attic or room above and slip its lower end into the fitting at the floor.

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