Remodeling Kitchens: Plumbing
Many kitchen remodels involve moving or extending existing plumbing and electrical runs. In some areas, local building codes may require you to hire licensed plumbers and electricians to do the work.
In any case, there are definite health, safety, and code issues involved in a kitchen remodel so consult your local building officials before starting.
They can tell you the codes and specific requirements dictating pipe and wire sizes, types of fittings and electrical boxes, the number of fixtures allowed on a run, and how much framing you can cut/drill out to make the necessary runs.
The following synopsis will give you a sense of what's involved and whether it's part of the project you want to handle yourself or hire out.
The first step for both plumbing and electrical rough-ins is to determine where the new fixtures will go so new runs can be laid out.
A new sink, for example, will usually be installed over a base cabinet and countertop. The sink plumbing and garbage disposer and dishwasher electrical circuits are generally run up the wall to where the cabinet will be installed.
Other electrical circuits are needed for each of the other major appliances. So determine locations for those receptacles first.
Drain-Waste-Vent (DWV) Rough-Ins
The DWV pipes are usually laid first because they're big, and it's easier to fit the water supply pipes and the electrical cables around them than vice versa.
The drain and vent pipes are most commonly plastic, either ABS (which is black) or PVC (which is white). We don't recommend mixing the types, because they expand/contract at different rates so leaks could develop. If you do join ABS and PVC, use mechanical fittings rather than glue.
If you're remodeling an existing kitchen and putting the new sink in the same spot as the old, just re-use the old DWV pipes. And if you're relocating the new sink just a bit, gluing short extensions on the existing pipes may work best.
Plumbers usually start runs at the top of the vent and work their way down. They run pipe across attic joists to the kitchen area, drill through the framing above the sink wall and run pipe down into the stud cavity.
If it's a two-story home, a small opening in an upstairs wall is often needed to glue the fitting and complete the run through the second floor.
The vent is cut so a glued on T-fitting will line up about 24 inches above the kitchen floor. A few inches of pipe are "stubbed out" to extend beyond the drywall and later connects to the drain pipe. But it's usually capped at this stage to prevent sewer gas from seeping into the house.
A hole is drilled through the bottom plate in the same stud cavity and through the sub-floor to run the drain pipe down into the basement.
From there the pipe has to be run at a downward slope (at least 1/4" per foot) to the soil stack where it's joined with another hubless T-fitting. Usually, one or more joists are drilled to allow for the run.
TIP: Remember to leave at least 5/8" of solid wood on each side of any holes you drill in the framing for strength and firestop the holes after running the pipe with insulation or mineral fiber to keep fire from spreading floor to floor.
Water Supply Rough-In
Hot and cold water pipes are usually copper, though plastic is sometimes used where codes allow. They have to run from the sink wall in the kitchen back to an existing set of pipes, usually in the basement. They're often run up into the same stud space as the DWV pipes but not always.
Holes are drilled through the bottom plate and floor. Each pipe runs up a foot or so into the stud space, is stubbed out a couple inches into the room and sealed shut with a cap.
In the basement, the pipe is run back to the source pipes with long pieces running between the joists and short coupled pieces going through the joists. A T- fitting is cut into each line to make the connections—after turning the water off, of course.
TIP: To avoid tearing into the walls to run new plumbing, you can often run the pipe alongside the wall and later frame a soffit or a false column or beam to hide it. Just remember to firestop the holes in the top and bottom plates.