How to Install a Basement Bathroom

Basement bathroom

 laughingmango / Getty Images

A basement bathroom improves the function of your home, and it adds real estate value like few other home improvements. But adding a full-function basement bathroom is no easy project. Few DIYers are really able to tackle all the tasks involved, and more often than not, this is a project best left to professionals. Most homeowners will hire a general contractor or individual subcontractors to handle all or most of the work. But understanding what goes into a basement bathroom will help you understand the complexity of the project and make it easier to work with pros. And who knows? You may even be able to do some or all of the work yourself.

Planning a Basement Bathroom Installation

Planning ahead will help you communicate with your pros and ensure you stay on target and within budget. Planning a basement bathroom has some unique considerations that are different from other home improvement projects.


A critical early step in the process, prior to any construction, is designing your new bathroom. In addition to determining the scope of the project, your bathroom design will also affect what permits and inspections are necessary. Positioning your new bathroom near existing utilities will reduce your workload and require fewer permits. If you can, place your basement bathroom below an existing first-story bathroom. This makes extending plumbing and wiring lines much easier.


Drainage is an important consideration when planning your basement bathroom. Above-ground plumbing relies on gravity to drain sewage and wastewater. This is known as the slope or fall of your drainage system. But many basement drains don’t provide adequate fall, making natural drainage a problem. As part of the planning process, have a professional examine the slope of your sewer lines and existing drain pipes. When the sewer exit point is above the level of a basement floor slab, for example, a basement bathroom will require special solutions for lift-pumping drain water to the sewer lines. Similarly, if your home uses a septic system, special solutions may be required.

Drainage Flow Rate

Have a pro examine the flow rate or your drainage system. A system that works fine for existing plumbing may become overtaxed when another basement bathroom is added. Low flow rates won’t properly evacuate waste and will result in clogs.

Backwater Valves

In many cases, city regulations may require backwater valves on basement drain lines. These are designed to ensure that sewage flow cannot reverse direction and flow back into the home. Ask a pro if a valve is necessary with your system.

Toilets for Basement Bathrooms

Toilets come in a wide range of options. Sometimes the same toilets used in above-grade bathrooms are perfectly fine in basements, but there are other designs that may be better choices:

  • Pressure-assisted toilets: Sometimes even deep basement lines with good slopes aren’t enough to clear sewage in basement bathrooms. Pressure-assisted toilets use air pressure to force wastewater through the lines, which can prevent clogs.
  • Composting toilets: Composting toilets require little water and turn your sewage into compost. These designs require excellent outside ventilation but can be a good choice where it is difficult to tap into existing sewer lines.
  • Sewage-ejector toilets: Ejecting toilets temporarily store sewage and then pump it into the sewer or septic line. These designs come in both above-ground and below-ground models.
  • Up-flushing toilets: Up-flushing designs are self-contained and hook directly into existing sewer lines. These toilets are perfect for homeowners wary of breaking up a basement floor to access sewer lines. Some up-flushing models also grind waste to prevent clogs.

Bathtubs, Showers, and Sinks for Basement Bathrooms

Adding additional plumbing fixtures to your basement bathroom may require the same prep and excavation as adding a toilet. Plumbing stub-outs may already be available in some basements, which makes breaking up the concrete floor unnecessary. Some up-flushing toilet systems also accept shower or sink connections. It’s best to have a pro examine your space and determine which kind of fixtures will work best for your bathroom.

Basement Lighting

The right lighting can make your basement bathroom as luxurious as your upstairs lavatories. Ample lighting can be even more important in basement bathrooms, since natural lighting may be quite limited. Wiring a basement bathroom is usually best left to professionals since these below-ground locations have special needs for ground-fault protection. Mistakes with electrical systems can cause personal injury, ruined fixtures, and fires, so unless you are a very skilled and knowledgeable DIYer, leave this to the pros.

Installation Overview

Installing a full-featured basement bathroom is a very complex DIY job. Unless you have extensive experience with carpentry, wiring, and plumbing installations, it’s best to hire pros for most aspects of this project. An even easier route is to have a general contractor (GC) manage the entire process, start to finish. An overview of the project will help you decide which steps if any, you might be qualified to handle.

  1. Lay out the walls: Bathroom walls are typically made from 2 x 4 or 2 x 6 horizontal wall and floor plates and vertical wall studs. While 2 x 4 lumber is more typical in most construction, "wet walls" that contain major plumbing lines are often built with 2 x 6 lumber, which provides more space for running the plumbing pipes. Normally, the outer walls are rough-framed before plumbing and wiring work begins, but in situations where concrete floors will need to be demolished, the wall locations may be simply marked, with wall framing completed later, after the main sewer line work is done. This framing work is normally done by a carpentry crew, but it's also possible for a skilled DIYer to do it.
  2. Position the shower and toilet drains: Using the manufacturer's specifications, the location for the shower drain and toilet floor flange are now established on the floor. Shower drains are usually dead center within the shower stall, but shower pans are also available with drain openings positioned off-center. Toilets are usually configured to sit 1 foot from back walls. When measuring for your toilet, be sure to include the extra 1/2 inch for the drywall. Also, make sure to allow proper spacing between the toilet and side walls.
  3. Dig trenches: The concrete floor is now demolished, and trenches are dug to connect the toilet and shower locations to the main sewer line. Additional trenching may also be needed for the vanity sink drain. Normally this is a job for a plumbing contractor, but some DIYers will take on this demolition work.
  4. Install underfloor drain pipes: The plumber will now connect the fixture drains into the main sewer line. This is usually a job for pros, not a DIYer.
  5. Install above-floor drains and vent pipes: The plumber now installs the above-floor branch drains and vent pipes, usually routing them through the new stud walls and connecting them to existing soil stacks and roof vent lines. In some situations, the plumber may run an entirely new soil stack all the way to the roof, creating a union with the new underground drain lines.
  6. Install water supply pipes: The plumber now installs water supply pipes or tubing to run from existing water pipes to the stub-out locations near the shower, toilet, and sink vanity locations. In most modern plumbing, this is now usually done with flexible PEX tubing, but traditional copper piping may also be used.
  7. Have rough-in plumbing inspected: With plumbing roughed in, but before the walls and floors are closed up, a city inspector will visit to review the plumbing work and certify that it has been done according to code and is a safe installation.
  8. Fill in trenches and pour concrete: With plumbing inspection done, the concrete floor can now be closed up by backfilling trenches and pouring new concrete. This is often done by the general contractor managing the job, but DIYers can also do it.
  9. Install electrical cables and boxes: An electrician now arrives to run electrical cables and install boxes for outlets and light fixtures.
  10. Have rough-in wiring inspected: With cables and electrical boxes installed, the rough-in electrical work is reviewed by a city inspector, who, if satisfied, will certify it as meeting code.
  11. HVAC work is roughed in and inspected: If the bathroom requires extensions or additions to the heating/cooling system, new ductwork is installed by a contractor and is inspected.
  12. Hang and finish wallboard: With plumbing, wiring, and HVAC work completed, the walls and ceilings can be covered with drywall, taped, and finished. If the work is being managed by a general contractor, his carpentry crew will do this work. DIYers can also perform his task.
  13. Lay flooring and shower tile: Flooring and shower surfaces are now installed. Subcontractors may do this work or the general contractor's crew. A very skilled DIYer can also tackle this work.
  14. Install cabinets: With the major surfaces of the bathroom now in place, the vanity and any other cabinetry are now installed. Usually, this is done by the carpenters employed by a general contractor, although some DIYers can tackle it.
  15. Install plumbing and wiring fixtures: The electrician and plumber now return to the job site to install the sink, toilet, faucets, light fixtures, outlet receptacles, and any other fixtures.
  16. Have final inspections done: Where required by law, a city inspector may be required to return to the job site to review and pass the final work.
  17. Finish paint and trim: The last step is usually painting the walls, and finishing and installing wood trim and moldings. Towel bars and any other hardware accessories are installed. This work is usually done by the contractor's carpentry crew, but many DIYers also take on this finish work.