Adding a Basement Bathroom

Planning & Design

As with any renovation project, one of the most important things to start out with is a realistic budget. Things will add up quick, and a typical basement renovation (with excavation to add new drain lines) will run you at least $10,000 on average. Get plenty of quotes for each aspect of the work you'll be contracting out, and do your research on materials and fixtures. If you look hard enough, there's a good chance you'll find great deals on (or even quality alternatives to) high‐ticket items.

Part of figuring out that budget is determining the kind of layout you want, and what the basement and rest of the house will accommodate.

• The easiest (and usually least expensive) basement bathroom location is directly below an existing bathroom upstairs, where connecting to the home's plumbing system won't be as much of a challenge.
• Half bathrooms (just a toilet and sink) are common in basements, given the (usually) limited space and the additional demands of a shower (another drain, waterproofing, better ventilation…)
• When a shower is desired, most go with a corner shower to save space. If the shower is going to be next to a toilet, you'll need to check your local plumbing code to find out the minimum distance between the two fixtures. If you have the space, consider putting the toilet in its own room.

Drainage

• If your basement has a floor drain and/or hookups for a washing machine or sink, it's a good start: if the drain is in a suitable location for the bathroom, very little excavation should need to be done!
• While it is possible to locate your home's main drain line yourself, your best bet is to call a plumber: they can use fancy tools to easily determine the depth and location. They might also be able to tell you the depth of the city sewer line for your property, which will determine whether your basement bathroom can drain by gravity or if it'll need assistance from a pump. You can also contact your public works department for sewer information.
• The drain lines for your basement fixtures will need to maintain the standard 1/4" slope to ensure adequate drainage by gravity. The city sewer will usually be deep enough below ground to allow for this, but the often flat (and concrete) floor of the basement may not provide enough of a fall for the drain line. The standard solution is to break up the concrete and dig a trench that allows the pipe to slope, and filling it back in. This is costly, but ultimately the best solution. When feasible, a properly designed and installed drain system will always be superior to pump‐driven alternatives.
• If you're going to be able to drain by gravity from the basement, your city will probably require a backflow preventer so that wastewater can't find its way back into the home in the event of a major sewage backup or a flood. This will likely require a permit, so be sure to find out ahead of time. You could also be required to have it installed or tested by a certified backflow technician. Though all this may seem like an inconvenience, it's absolutely worth it!

Ventilation

• Each fixture will need to be vented, which can become complicated in a basement. Newer homes may have some basement plumbing already roughed‐in, including a vent opening through the roof that can be connected to. Otherwise, there are numerous possibilities and solutions — yours will depend on what's allowed locally. Unless you're experienced with bathroom ventilation (and familiar with local code), this is best left to a licensed plumber.
• You may be able to tie into an existing vent system for basement fixtures (like for a floor drain or utility/laundry sink) or a first‐floor bathroom (if you can connect to the vent stack 6" above the flood level of the highest fixture, as dictated by code). Again, to avoid problems and pass inspection, we highly recommend letting a licensed plumber design the basement DWV system.
• It's not just the fixtures that need ventilation: the room itself must be well‐ventilated to remove moisture that can lead to big problems down the road. This is especially important when a shower is present, but is a good idea regardless. Code will often accept a mere window to meet room ventilation requirements, but an exhaust fan is always the better option. These fans can usually be vented horizontally out a side wall like a dryer vent.

Excavation Alternatives

If digging for a new drain line isn't an option, hope is not lost: there are several alternatives to excavation that can make your basement bathroom a reality! Keep in mind, however, that each of these options will still need to be vented according to code (almost always through the roof).

• Sewage Ejector Systems utilize a holding tank/basin and pump to send wastewater from all basement fixtures to the home's main drain, where it then joins the rest of the home's wastewater in travelling to the city sewer (via gravity). Traditional belowground versions require digging a pit for the basin as well as a trench for the pipe that carries waste to it. Freestanding versions that sit above ground require fixtures to be raised above ground level so they can drain into the basin.
• Upflush or Macerating Toilets connect directly to special pump that grinds up (or macerates) the waste moving through it. This makes it easier for the pump to move that waste all the way to the home's main sewer line. The big selling point for these units is that they don't require any digging: the toilet and pump are installed above ground (for a cleaner look, the pump can often be installed behind a wall). So while the toilets are somewhat expensive, you'll save a ton by not having to excavate. You can even connect sink and shower drains to these systems! Grinder pumps are available á la carte as well, which can be used with most any rear‐outlet toilet. View our page for tips on macerating toilets.
• Composting Toilets are a more environmentally‐friendly solution to the challenge of putting a toilet in the basement. Foregoing the use of plumbing and water, they instead rely on heat (generated by electricity) and a fan system to evaporate the water content of waste (in most designs liquid waste is stored separately for disposal). Waste goes into a tank (along with "bulking materials" like peat moss or coconut coir), which is rotated after each use by cranking a handle. At capacity, the tank must be manually emptied; the contents can be further composted in a bin for eventual garden use, or thrown out in the garbage.