How to Install a Basement Bathroom

Wood and Tile Floor in Contemporary Bathroom
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Basement bathrooms improve the utility and value of your home, but installing a lower-level lavatory can present a few challenges. Here’s a look at the important considerations of a basement bathroom and a quick construction how-to.  

Important Considerations

Planning ahead will help you communicate with your pros and ensure you stay on target and within budget. Use these details to help you organize your installation plans.

  • Design: Designing your new bathroom is a critical step of the construction process. In addition to determining the scope of your project, your bathroom design will also affect your licensing, permits and zoning. Building 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 lavatory. This makes extending utilities easier.
  • Drainage: 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. Some basement drains don’t provide adequate fall, making natural drainage a problem. Have a professional examine the slope of your basement drain if you don’t have experience installing plumbing. Installing shallow plumbing will result in major repairs. It’s important to also ensure your septic tank lines are deep enough.
  • Flow Rate: Have a pro examine your flow rate. Low flow rates won’t evacuate waste and will result in clogs. In many cases, city lines require backwater valves. Installing a backwater valve may require a permit. Ask a pro if a valve is necessary with your system.

Toilets

Toilets come in a wide range of options.

Here’s a look at the most popular models:

  • Pressure-Assisted Toilets: Sometimes even deep basement lines aren’t enough to clear sewage. Pressure-assisted toilets use air pressure to force waste water through the lines and prevent clogs.
  • Composting Toilets: Composting toilets require little water and turn your sewage into compost. These designs require excellent outside ventilation.
  • Sewage-Ejector Toilets: Ejecting toilets temporarily house 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 weary of breaking their basement floor. Some up-flushing models also grind waste to prevent clogs.

Bathtubs, Showers and Sinks

Adding additional plumbing fixtures to your basement bathroom will require the same prep and excavation as adding a toilet. Plumbing stubs are available in some basements, which makes breaking up your flooring 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.

Lighting

The right lighting can make your basement bathroom as luxurious as your upstairs lavatories. But providing your space with power is a job that’s best left to professional electricians. Mistakes with electrical systems can cause personal injury, ruined fixtures and fires.

Installing the Bathroom

Installing a basement bathroom isn’t a simple DIY job. Unless you have extensive experience with carpentry and plumbing installations, it’s best to hire a pro. Here’s a quick guide to get your basement bathroom started.

  1. Install Wall Plates: Use two-by-fours to determine the perimeter of your bathroom and create your wall plates. Mark the location of fixtures on the wall plates. Your wall plates will be the basis for the rest of your measurements. Be sure your dimensions are correct before beginning the next step.
  1. Find the Shower Drain: Mark your shower location and divide the total size of your shower by two to locate your drain. For example, if you have a 48-square-inch shower, measure 24 inches from both sides of the wall. This will be the location of your shower drain.  
  2. Locate Your Toilet Flange: Most toilets need to be one foot from your finished wall. When measuring for your toilet, be sure to include the extra one-half inch for the drywall. This is the location of your toilet flange.

  3. Dig a TrenchUncover your existing drain pipe and dig a trench connecting it with your shower drain and toilet flange. In many cases this will require breaking concrete. Be sure not to disturb your drain pipe during this process. Pro Tip: Use a diamond-plated grinder wheel to cut through older cast-iron drain pipes.

  4. Attach Your PVC: If your drain and PVC are different sizes or materials, use a mechanical coupling to join the two.
  5. Connect Your Drains: Use piping and fittings to connect your drains. In many cases, two-inch pipe is best to connect your pipes and drain. Only do a dry fitting (no glue) until your measurements are perfect.
  6. Add Your Traps: Install traps at the end of each pipe. Make sure your pipes slope one-eighth inch per foot to ensure proper draining.
  7. Reinforce Your Traps: Drive rebar on either side of your pipe and duct tape it to your PVC. This will hold your pipes and traps steady during the concrete pouring.
  8. Schedule an Inspection: Have a local inspector double check your plumbing to ensure your job is up to code.
  9. Pour Your Concrete: Hire a concrete contractor to pour your concrete. Be sure to cover the toilet pipes with a foam cap and wrap the shower drain in plastic.