Half Bath

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A first-story half bath is easy to install when located behind a kitchen or existing bathroom, because you can take advantage of accessible supply and DWV lines. It is possible to add a half bath on an upper story or in a location distant from existing plumbing, but the complexity and cost of the project may be increased considerably.

 

Difficulty Level:
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Continue to Step 1

Overview

A first-story half bath is easy to install when located behind a kitchen or existing bathroom, because you can take advantage of accessible supply and DWV lines. It is possible to add a half bath on an upper story or in a location distant from existing plumbing, but the complexity and cost of the project may be increased considerably.
Be sure that the new fixtures are adequately vented. We vented the pedestal sink with a pipe that runs up the wall a few feet before turning to join the main stack. However, if there are higher fixtures draining into the main stack, you would be required to run the vent up to a point at least 6" above the highest fixture before splicing it into the main stack or an existing vent pipe. When the toilet is located within 6 ft. of the stack, as in our design, it requires no additional vent pipe.
The techniques for plumbing a half bath are similar to those used for a master bathroom.
In this half bath, the toilet and sink are close to the main stack for ease of installation, but are spaced far enough apart to meet minimum allowed distances between fixtures. Check your local code for any restrictions in your area. Generally, there should be at least 15" from the center of the toilet drain to a side wall or fixture, and a minimum of 21" of space between the front edge of the toilet and the wall.

From: The Complete Guide to Plumbing, 978-1-58923-378-2

What You'll Need

Tools:

Drill
Circular Saw

Materials:

3" x 1 1⁄2" reducing Y and 45
or a 3" x 1 1⁄2" reducing TY combo
closet bend
3" drain pipe
1 1⁄2" drain pipe
3⁄4" x 1⁄2" reducing T-fittings
1⁄2" copper supply pipes
drop ear elbows
vertical vent pipe
vent T

 

Step 1

How to Plumb a Half Bath

Locate the main waste-vent stack in the wet wall, and remove the wall surface behind the planned location for the toilet and sink. Cut a 4 1⁄2"-diameter hole for the toilet flange (centered 12" from the wall for most toilets). Drill two 3⁄4" holes through the sole plate for sink supply lines and one hole for the toilet supply line. Drill a 2" hole for the sink drain.


Step 2

How to Plumb a Half Bath

In the basement, cut away a section of the stack and insert a waste T-fitting with a 3" side inlet for the toilet drain; below that, insert a 3" x 1 1⁄2" reducing Y and 45, or a 3" x 1 1⁄2" reducing TY combo for the sink. Install a closet bend and 3" drain pipe for the toilet, and install a 1 1⁄2" drain pipe with a sweep elbow for the sink. Make sure to maintain the proper 1⁄4" per foot slope of the drain pipes.


Step 3

How to Plumb a Half Bath

Tap into water distribution pipes with 3⁄4" x 1⁄2" reducing T-fittings, then run 1⁄2" copper supply pipes through the holes in the sole plate to the sink and toilet. Support all pipes at 4-ft. intervals with strapping attached to joists.


Step 4

How to Plumb a Half Bath

Attach drop ear elbows to the ends of the supply pipes, and anchor them to blocking installed between studs. Anchor the drain pipe to the blocking, then run a vertical vent pipe from the waste T-fitting up the wall to a point at least 6" above the highest fixture on the main stack. Then, route the vent pipe horizontally and splice it into the vent stack with a vent T.


 
 

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