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Roughing in Tubs, Showers, and Toilets

Plan the location of your bathroom fixtures carefully: A couple of inches one way or the other can make the difference between a bathroom that is comfortable and one that feels cramped and inconvenient. Begin by mapping the floor of your bathroom on a piece of graph paper. Cut out small-scale pieces of paper that represent the fixtures. Move the pieces until you find the most usable configuration. If a door opens inward, make sure it can swing completely without hitting a fixture. The dimensions given in the drawings at right show the minimum requirements for ease of use. Do not place fixtures closer to each other than specified. Once you decide on your floor plan, mark your floors and walls for the rough-in dimensions, using the dimensions shown below right.

Finding Drainpipes

  • Before you figure how to rough in your new drains, you need to find the existing drain. Start at the basement or crawl space. If you see a 3- or 4-inch stack, it probably runs straight up through the roof. Or look for a plumbing access panel. You may have one on the other side of the wall behind your bathroom fixtures. (Often you’ll find it in a closet.) Remove the access panel and peer inside with a flashlight.
  • If you notice a wall is thicker than the standard 4 1/2 inches, chances are it contains drainpipes. Toilets usually are placed near stacks.

Once you’ve finished planning, cut holes in your walls and floors for installing drain lines and supply stubs, the supply lines that stick out a bit from the wall and are ready to accept stop valves. Patching walls and floors can be more time-consuming than the plumbing itself. Where possible, limit your cuts to areas that will be covered by the fixtures. Cut drywall or plaster neatly so it can be patched easily. Don’t forget to install venting.

Rough-in a sink. If you are installing a vanity cabinet, you have latitude for placing the drain and supply stubs. For a wall-hung sink or a pedestal sink, hold the fixture up against the wall and mark the best locations for drain and supply stubs. In most cases, it is best to position the supply stubs within 12 inches of the faucet.

Rough-in a toilet. Be careful to place the closet bend the correct distance from the wall—usually 12 inches to the center of the drain. (Double-check the requirements for your toilet.) A closet flange will sit on top of the floor after you have patched and surfaced it. Only a cold water supply stub is needed. Place it where it will be unnoticeable.

Rough-in a shower only. To correctly position the drain, set the base in place and measure from the walls. Allow for wall surfacing. To spare patching later, cut the floor so the base will cover the hole. Install a P-trap below the level of the floor at the level required by the drain assembly kit. Install the control assembly. Its pipe determines how far apart the supply pipes should be. Firmly attach the shower pipe to framing.

Rough-in a tub and shower. Cut the floor so the tub will cover the hole. Install a P-trap and bathtub drain assembly. It will be somewhat unstable until you connect it to the tub. The one-handle control shown requires that supplies be plumbed horizontally into it. Attach the control and the top of the shower pipe firmly to framing; you will probably need to frame in a piece of lumber between the studs.

Rough-in a two-handle control. A two-handle control is easier to install. Set the hot and cold pipes at the same height. Attach the control and the top of the shower pipe elbow to frame supports.

Caution! Don't Weaken Joists - Deep notches greatly reduce the strength of joists. Drill holes if possible, or reinforce joists after notching.

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