Plumbing a Master Bath Part 1 of 3

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A large bathroom has more plumbing fixtures and consumes more water than any other room in your house. For this reason, a master bath has special plumbing needs.

 

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Overview

A large bathroom has more plumbing fixtures and consumes more water than any other room in your house. For this reason, a master bath has special plumbing needs. Frame bathroom “wet walls” with 2 x 6 studs, to provide plenty of room for running 3" pipes and fittings. If your bathroom includes a heavy whirlpool tub, you will likely need to strengthen the floor by installing “sister” joists alongside the existing floor joists underneath the tub. Check with your local codes.
For convenience, our project is divided into the following sequences:
• How to Install DWV Pipes for the Toilet & Sink
• How to Install DWV Pipes for the Tub & Shower
• How to Connect Drain Pipes to a Main Waste-Vent Stack
• How to Install the Water Supply Pipes
From: The Complete Guide to Plumbing, 978-1-58923-378-2

What You'll Need

Tools:

Hole saw
Circular saw
Solvent glue
Drill
Jigsaw

Materials:

Hole saw
Circular saw
Solvent glue
Drill
Jigsaw

 

Step 1

Bathroom Features

Our demonstration bathroom is a second-story master bath. We are installing a 3" vertical drain pipe to service the toilet and the vanity sink, and a 2" vertical pipe to handle the tub and shower drains. The branch drains for the sink and bathtub are 1 1⁄2" pipes—for the shower, 2" pipe. Each fixture has its own vent pipe extending up into the attic, where they are joined together and connected to the main stack.


Step 2

How to Install DWV Pipes for the Toilet & Sink

Use masking tape to outline the locations of the fixtures and pipe runs on the subfloor and walls. Mark the location for a 3" vertical drain pipe on the sole plate in the wall behind the toilet. Mark a 41⁄2"-diameter circle for the toilet drain on the subfloor.


Step 3

How to Install DWV Pipes for the Toilet & Sink

Cut out the drain opening for the toilet, using a hole saw. Mark and remove a section of flooring around the toilet area, large enough to provide access for installing the toilet drain and for running drain pipe from the sink. Use a circular saw with blade set to the thickness of the flooring to cut through the subfloor.


Step 4

How to Install DWV Pipes for the Toilet & Sink

If a floor joist interferes with the toilet drain, cut away a short section of the joist and box-frame the area with double headers. The framed opening should be just large enough to install the toilet and sink drains.


Step 5

How to Install DWV Pipes for the Toilet & Sink

To create a path for the vertical 3" drain pipe, cut a 4 1⁄2" x12" notch in the sole plate of the wall behind the toilet. Make a similar cutout in the double wall plate at the bottom of the joist cavity. From the basement, locate the point directly below the cutout by measuring from a reference point, such as the main waste-vent stack.


Step 6

How to Install DWV Pipes for the Toilet & Sink

Measure and cut a length of 3" drain pipe to reach from the bathroom floor cavity to a point flush with the bottom of the ceiling joists in the basement. Solvent-glue a 3" x 3" x 11⁄2" Y-fitting to the top of the pipe, and a low-heel vent 90° fitting above the Y. The branch inlet on the Y should face toward the sink location; the front inlet on the low-heel should face forward. Carefully lower the pipe into the wall cavity.


Step 7

How to Install DWV Pipes for the Toilet & Sink

Lower the pipe so the bottom end slides through the opening in the basement ceiling. Support the pipe with vinyl pipe strap wrapped around the low-heel vent 90° fitting and screwed to framing members.


Step 8

How to Install DWV Pipes for the Toilet & Sink

Use a length of 3" pipe and a 4 x 3 reducing elbow to extend the drain out to the toilet location. Make sure the drain slopes at least 1⁄4" per foot toward the wall, then support it with pipe strap attached to the joists. Insert a short length of pipe into the elbow so it extends at least 2" above the subfloor. After the new drains are pressure tested, this stub-out will be cut flush with the subfloor and fitted with a toilet flange.


Step 9

How to Install DWV Pipes for the Toilet & Sink

Notch out the sole plate and subfloor below the sink location. Cut a length of 1 1⁄2" plastic drain pipe, then solvent-glue a waste T to the top of the pipe and a sweep 90° elbow to the bottom. Note: The distance from the subfloor to the center of the waste-T should be 14" to 18”. The branch of the T should face out, and the discharge on the elbow should face toward the toilet location. Adjust the pipe so the top edge of the elbow nearly touches the bottom of the sole plate. Anchor it with a 3⁄4"-thick backing board nailed between the studs.


Step 10

How to Install DWV Pipes for the Toilet & Sink

Dry-fit lengths of 1 1⁄2" drain pipe and elbows to extend the sink drain to the 3" drain pipe behind the toilet. Use a right-angle drill to bore holes in joists, if needed. Make sure the horizontal drain pipe slopes at least 1⁄4" per foot toward the vertical drain. When satisfied with the layout, solvent-glue the pieces together and support the drain pipe with vinyl pipe straps attached to the joists.


 
 

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