The Ultimate Guide to Bathroom Plumbing Diagrams and Layouts

Planning a bathroom remodel? Find tips and information on bathroom layouts, minimum clearances, choosing materials, standard dimensions, pipes, and more before you start construction.

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Before deciding on a shower head, a few more critical decisions must be made in a bathroom remodel. Specifications for the placement of plumbing fixtures and the dimensions of pipes are intended to make the bathroom a comfortable space with plenty of capacity for incoming water and outgoing drains and vents. The specs shown here will meet the requirements of most building departments, but check local codes to be sure.

Tips for Bathroom Layouts

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Placement of the toilet, sink, and tub may depend partly on the existing plumbing. For example, most homes will have a "wet wall," an interior wall thicker than most walls because it contains water lines and the main stack. Minimize long horizontal runs of drain and vent pipes by installing fixtures on or close to the wet wall.

Plan for a layout that's comfortable and convenient. The following pages show the bathroom plumbing diagram and how to install a basic 5x8-foot bathroom—just enough room for the three major fixtures with adequate space between them.

Most codes require no fixture being closer than 15 inches from a toilet's centerline. There must be at least 24 inches in front of the toilet, but it's OK for a door to swing into this space.

Sinks and vanity sink tops range from 20 to 30 inches in width. A standard bathtub is 60 inches long by 32 inches wide. If your plans call for a larger tub, alter the layout to fit it.

The framed opening—not the finished wall—must be 60 inches long to accommodate a standard tub. If the opening is any smaller, the tub will not fit; if the opening is more than 1/4 inch too long, making a tight seal along the wall will be difficult. The framing must be almost perfectly square.

Choosing Materials

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These plans call for a 3-inch-diameter PVC pipe for the main drain and the short length leading from the toilet to the drain, and a 2-inch PVC for the other drain lines and the vents. Local codes may call for a 4-inch main drain, and some plumbers prefer to run larger vent pipes.

Cast-iron drainpipe is coming back in some areas because it's quieter than plastic pipe. However, cast-iron pipe should be installed by a pro. (You can reduce the noise of water draining through PVC by wrapping the pipe with insulation.)

Rigid copper pipe is the most common material for water-supply lines, but PEX or other plastic materials may be permitted in your area. Bathrooms are usually supplied with 1/2-inch pipe. Run 3/4-inch pipe to the bathroom for maximum water pressure and use 1/2-inch for short runs only.

Related: 36 Breathtaking Walk-In Shower Ideas

Minimum Clearances

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A bathroom with a 5x8-foot interior space allows the minimum clearances that most municipal codes require for fixtures. While exploring layout options, maintain these clearances in your plan to ensure ease of use and installation.

Related: How to Plan the Best Bathroom Layout Plans for Your Space

Plan Vents and Drain Lines

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Once you've decided on the basic layout and have a general idea of how the drain and vents will run, make specific bathroom plans. Measure the existing room plan for new framing, considering the thickness of the wall finishing material—usually 1/2 inch for drywall and perhaps another 3/8 inch for wall tiles.

Vents Start by figuring out where the vents will go. As a general rule, the drain line for each fixture should connect to a vent within a few feet of the fixture. An actual vent never has water running through it. However, wet venting—routing drain water through a vent—is permitted in some situations.

This plan calls for running a new vent through the ceiling and either tying into an existing attic vent or running through the roof. You also might be able to tie into an existing vent on the same floor. Consider how new lines will affect existing vents. For instance, if you install an upper-story bathroom and tie into an existing stack, you may drain water through a pipe that's currently used as a vent.

Drains In this plan, a new main drain line for the bathroom runs down to the floor below. If the new bathroom is on the first floor, you can probably just tie it into the house's main drain line in the basement or crawlspace below.

If the new bathroom is on the second floor, the main drain will have to travel through the wall on the first floor and down to the basement or crawlspace. If a drain line is nearby, you may choose to run a pipe to it rather than running a new line. However, running a toilet's 3-inch (or 4-inch) drain to an existing line may be difficult, especially if you have to go through joists.

IThe drain lines in the room below the installation turn outward at 45-degree angles to avoid running 3- or 4-inch pipe through studs. If the room below is finished, you'll need to build a soffit around the pipes or run them through the studs. This plan calls for a 3-inch horizontal drain; codes may permit 2-inch pipe.

Seal openings where pipes enter attics or crawlspaces to prevent drafts and to act as fire stops.

Consider Your Drain-Waste-Vent System

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The pipes supplying hot and cold water can run in any convenient configuration. However by running separate 3/4-inch lines from near the water heater to the shower, water pressure (and temperature) will not be affected when someone uses another fixture in the house.

Related: Everything You Need to Know About Venting for Successful DIY Plumbing Work

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