The new bath must comply with standard plumbing practices.
Ask any family what feature they would most like to add to their existing home and many will agree that another bathroom tops their wish list. In a two-story home, adding a bathroom upstairs involves choosing a location that allows you to tie the bathroom drainage system into the main house drainage system.
Configuration
Locating the second floor bathroom directly over a main floor bathroom minimizes plumbing configurations, but not all homeowners want the new bathroom in that spot. Before choosing the location of the bathroom, calculate the acceptable "fall" of the drain pipes at the rate of 1/4 inch per linear foot. The pipes will run through the joists beneath the bathroom floor until they can descend through a stud wall. A plumbing diagram is essential because it allows you to determine the configuration of the drain system. Generally, the closer the new bathroom sits to the main drainage system, the better.
Water Supply
Running water supply lines is a simpler process than running drain lines. Water supply lines are much narrower, and often are made from flexible tubing that runs through the walls from the water distribution system to the bathroom fixtures. The tub, sink and shower will require hot and cold water supply plumbing, while you will provide only cold water to the commode.
Drainage
Sinks, tubs and showers require P-traps installed beneath their drains. The sink drain sits higher, so the P-trap will fit under the sink cabinet. Because a shower or tub drain, however, sit close to the floor, the P-trap must be located beneath the floor, between the joists. The commode sits on a flange on the floor and, due to the wider drainpipe and the toilet design, it does not require the addition of a P-trap. As soon as the allows, the sink and tub/shower drains will join the commode drain. From there, the drainpipe should slope downward at the acceptable fall rate. When the drainage pipe reaches a vertical wall, it will drop down between wall studs and then will continue the sloped descent until it ties into the main drainage system.
Venting the Plumbing
For the new bathroom to drain with ease, the must be vented. The drain line attached to each fixture will have a vent line that extends upward. The vent lines will connect at a common point, just as the drain lines do. Your home has a main plumbing vent that runs upward and eventually exits through the roof. Without the plumbing vent system, the water in the drain pipes can form a vacuum seal, stopping all drainage. The vent system introduces air into the pipes and prevents water locks. A licensed plumber should inspect and approve the vent system.
Tags: drainage system, drain pipes, vent system, acceptable fall, choosing location, cold water