Plumbing a Master Bath Part 2 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

How to Install DWV Pipes for the Toilet & Sink

In the top plates of the walls behind the sink and toilet, bore 1⁄2"-diameter holes up into the attic. Insert pencils or dowels into the holes, and tape them in place. Enter the attic and locate the pencils, then clear away insulation and cut 2"-diameter holes for the vertical vent pipes. Cut and install 11⁄2" vent pipes running from the toilet and sink drain at least 1-ft. up into the attic.


Step 2

How to Install DWV Pipes for the Tub & Shower

On the subfloor, use masking tape to mark the locations of the tub and shower, the water supply pipes, and the tub and shower drains, according to your plumbing plan. Use a jigsaw to cut out a 12" square opening for each drain, and drill 1"-diameter holes in the subfloor for each water supply riser.


Step 3

How to Install DWV Pipes for the Tub & Shower

If installing a large whirlpool tub, cut away the subfloor to expose the full length of the joists under the tub, then screw or bolt a second joist, called a sister, against each existing joist. Make sure both ends of each joist are supported by loadbearing walls.


Step 4

How to Install DWV Pipes for the Tub & Shower

In a wall adjacent to the tub, establish a route for a 2" vertical waste-vent pipe running from basement to attic. This pipe should be no more than 31⁄2 ft. from the bathtub trap. Then, mark a route for the horizontal drain pipe running from the bathtub drain to the waste-vent pipe location. Cut 3"-diameter holes through the centers of the joists for the bathtub drain.


Step 5

How to Install DWV Pipes for the Tub & Shower

Cut and install a vertical 2" drain pipe running from basement to the joist cavity adjoining the tub location, using the same technique as for the toilet drain (steps 4 to 6). At the top of the drain pipe, use assorted fittings to create three inlets: branch inlets for the bathtub and shower drains and a 11⁄2" top inlet for a vent pipe running to the attic.


Step 6

How to Install DWV Pipes for the Tub & Shower

Dry-fit a 11⁄2" drain pipe running from the bathtub drain location to the vertical waste-vent pipe in the wall. Make sure the pipe slopes 1⁄4" per foot toward the wall. When satisfied with the layout, solvent-glue the pieces together and support the pipe with vinyl pipe straps attached to the joists. If local codes require vents for each fixture, add a vent pipe and T-fitting.


Step 7

How to Install DWV Pipes for the Tub & Shower

Dry-fit a 2" drain pipe from the shower drain to the vertical waste-vent pipe near the tub. Install a solvent-glued trap at the drain location, cut a hole in the sole plate, and insert a 2" x 2" x 1 1⁄2" vent T within 5 ft. of the trap. Make sure the drain is sloped 1⁄4" per foot downward away from the shower drain. When satisfied with the layout, solvent-glue the pipes together.


Step 8

How to Install DWV Pipes for the Tub & Shower

Cut and install vertical vent pipes for the bathtub and shower, extending up through the wall plates and at least 1 ft. into the attic. These vent pipes will be connected in the attic to the main waste-vent stack. In our project, the shower vent is a 2" pipe, while the bathtub vent is a 11⁄2" pipe. When you have completed all the DWV piping, cover large cutouts to sill plates with boards and stuff fiberglass insulation or use fire-rated foam insulation to create a fire stop.


Step 9

How to Connect Drain Pipes to a Main Waste-vent Stack

In the basement, cut into the main waste-vent stack and install the fittings necessary to connect the 3" toilet-sink drain and the 2" bathtub-shower drain. In our project, we created an assembly made of a waste T-fitting with an extra side inlet and two short lengths of pipe, then inserted it into the existing waste-vent stack using banded couplings. Make sure the T-fittings are positioned so the drain pipes will have the proper downward slope toward the stack.


Step 10

How to Connect Drain Pipes to a Main Waste-vent Stack

Dry-fit Y-fittings with 45° elbows onto the vertical 3" and 2" drain pipes. Position the horizontal drain pipes against the fittings, and mark them for cutting. When satisfied with the layout, solvent-glue the pipes together, then support the pipes every 4 ft. with vinyl pipe straps. Make sure to maintain the proper 1⁄4" per foot downward slope in all waste pipes.


 
 

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