Plumbing a Basement Bathroom
Cutting through the slab is grunt work of the highest order, but a relatively easy way to get an extra bath.
Synopsis: Adding a basement bathroom is just like adding a bath anywhere else in the house — except for cutting through the basement’s concrete-slab floor. Rhode Island contractor and Fine Homebuilding contributing editor Mike Guertin outlines his strategy for adding a basement bath, starting with planning the drain layout. This crucial step ensures that plumbing is located so that wastewater flows downhill to a tank; from there, it is pumped to the main waste line and out of the house. It’s also important to tie in vent lines for the basement fixtures.
Adding a bathroom in a basement might sound like a complicated project, but the plumbing part of the job isn’t much different than any above-grade bath. It’s simple and straightforward to bring in the small-diameter supply lines for hot and cold water. Cutting the slab and digging the trench for the waste lines are the tasks that set this project apart. I work with my plumber, Paul Murray, to map out the best fixture layout, and we then divide the tasks required to complete the project. I tackle the slab work, and he lays the drain and supply piping. Of course, the sewer-outlet pipe on most of my projects is above the basement-floor elevation, so we have to install a tank to collect the sewage and a pump to send it up to the level of the sewer outlet. The roughin process takes several days for us to complete; then we can schedule the inspections.
Plan the drain layout first
Rather than completely breaking out the concrete slab in the prospective bathroom, I cut trenches where the drains will run. This saves me from having to move lots of broken concrete and then repour the slab. I chalk a proposed fixture layout on the concrete…