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Adding a Bathroom to Your Basement: Design & Drainage Considerations

Posted on: July 17, 2013

Adding a bathroom to basement areas not only makes your life a little easier, it also boosts your property value. If you’ve turned your finished basement into a spare bedroom, game room, or exercise room, a basement bathroom lets you enjoy that space without having to trudge upstairs when nature calls.

As smart as this home improvement project may seem, though, building a bathroom in the basement isn’t something to rush into. Several issues make belowground plumbing projects more complicated than those on upper floors. Address those issues before you start, and you should go off without a hitch.

Even if you’ve built a bathroom in your home before, the added complexity of belowground plumbing means adding a bathroom to basement areas is a job best left to a plumbing professional. Still, getting familiar with the requirements of the project will make it easier to work with your contractor to create exactly the bathroom design you want. Knowing what adding a bathroom to basement areas entails also helps you plan your budget.

Design considerations

Your first step should be to contact your local building authority. With any building project, particularly in a basement, there are likely to be zoning ordinances and deed restrictions you’ll need to consider.

Ideally, aim to locate the new bathroom as close to existing plumbing and electrical wiring as possible. Situating your basement bathroom directly below the one on the floor above often works best. This makes utility hookups easier and less expensive.

The type of bathroom you want is your next consideration. Do you want a full bathroom complete with a bathtub or stand-up shower, or would you be content with a half-bath with just a toilet and sink?

Because basements tend to be damp and chilly, you may want to skip the tub or shower unless it’s truly necessary.

If you do want a place to get clean, consider an economical corner shower rather than a bathtub. Give heating and waterproofing some extra consideration, too. A high-power ventilation fan to draw out moisture is absolutely essential.

Including a laundry area when adding a bathroom to basement areas is another option, but it brings added complexities. You’ll need a floor drain to manage overflows and access to an exterior wall for the dryer vent.

Drainage considerations

Drainage is the most critical consideration when adding a bathroom to basement spaces. Standard aboveground bathroom plumbing relies on gravity to drain away sewage and wastewater. Gravity provides a push, known as a “fall” or “slope,” that moves waste down the pipes. In a basement bathroom, there must be enough of a fall to drain the toilet, sink, tub, or shower.

When inspecting your basement for a new bathroom installation, your contractor will consider two main issues first.

  1. Plumbing depth — If your existing plumbing drain is deep enough to create enough fall for drainage, bathroom construction will be relatively easy. If not, you’ll need to consider some alternative options to standard gravity-fed toilets.
  2. Pipe size — If your existing pipes are too small, your plumber will need to put in larger pipes to allow space for the basement drains.

Your sewer line may be deep enough to allow your basement bathroom plumbing to work on gravity just as your aboveground plumbing does. Your local public works department can provide you with information on the depth of your sewer line. If you have a septic tank, you’ll need to find out if your home’s septic lines are deep enough with the information you probably have on hand.

In fact, if your home was built with the intention of installing a basement bathroom, there may be plumbing stubs available already. This makes installation considerably easier.

Even if your drain lines are deep enough, there are still some special considerations. Your plumber will need to determine the flow rate to ensure it’s sufficient to remove waste. If you’re on a city sewer line, you’ll need a backwater valve to keep sewage from backing up into your toilet. Installing this valve may require a permit, so your plumber will need to know before starting the project.

If your drainage lines aren’t deep enough to create enough fall, you’ve got some extra work ahead of you. You may need to remove part of your basement floor and excavate the ground below it. For some homes, though, that still won’t be enough to create sufficient fall, but that doesn’t mean you have to give up on your project. Adding a bathroom to basement areas like this requires specially designed equipment, but it’s still doable.

Basement toilet options

Depending on your existing plumbing, you have a number of choices of commodes for your new bathroom.

Pressure-assisted toilets — Although your drainage lines may technically be deep for gravity-fed plumbing, the fall still isn’t as strong in the basement as it is on upper floors. Instead of risking clogs with standard plumbing, choose a pressure-assisted toilet that uses air pressure to force waste through the pipes.

Upflushing toilets — An upflushing toilet is a self-contained unit that sits on the floor, so you don’t have to remove any concrete or excavate to install one. The plumbing lines run upward through the wall to the basement ceiling and connect to the sewer or septic tank line there. This is one of the simplest options for adding a bathroom to basement areas.

Some of these models include a macerating function that grinds waste down to prevent clogging. Older upflushing macerating models relied on water pressure for this grinding, which caused odor and overflow issues. New models work on electricity, which eliminates these problems.

Sewage-ejector systems
— Sewage-ejector tank-and-pump systems are designed to pump sewage upward to the sewer or septic tank line. They’re like small septic tanks in that they hold waste temporarily. These come in both aboveground (free-standing) and belowground versions. Aboveground models sit on the floor, so installing one requires no excavation. The toilet is positioned on top of an enclosed tank and pump unit. Your sink and bathtub or shower can also drain into this tank.

Belowground sewage-ejector systems are also available. These units involve a tank and pump that sit in a hole below your basement floor. This allows your fixtures to drain into the unit using gravity. Because they require excavation, though, they’re more work to install than aboveground models.

Composting toilets — One of the most eco-friendly solutions, composting toilets use little to no water and turn your waste into compost you can use for decorative plants. On the downside, they’re designed only for toilet waste (but not sink or shower wastewater) and require good outside ventilation.

Installing bathtubs or showers

Installing a tub or shower in your basement carries many of the same concerns as installing a toilet. You may need to break up the floor and excavate to install the plumbing. Again, if plumbing stubs are available, you can install a shower as you would in any other room. Alternatively, you can connect your shower to your upflush toilet or sewage-ejector system.

Lighting considerations
Good lighting in the bathroom is a must for comfort, but underground bathrooms face certain challenges in this area. If you’re locating your basement bathroom against an aboveground exterior wall, use the opportunity to bring natural light into the room. Glass-block windows are one easy way to let in daylight without compromising privacy. In addition, choose bright ceiling lights and lights for the vanity area.

Adding a bathroom to basement areas gives finished basements an extra touch that makes them feel just like any other level of your home. With the right layout, fixtures, and decor, your basement bathroom can be as luxurious as your main bathroom.

Building a basement bathroom is no simple task, though, even for a relatively experienced home-improvement enthusiast. Overlooking any of the aspects that make belowground bathrooms different from aboveground ones can leave you with an expensive mess.

In addition to finding a plumber for your basement construction project, you may also want to contact a building contractor to frame the bathroom walls. If you’re experienced in construction, though, this is something you can get done yourself. The plumbing, on the other hand, isn’t something to take chances with.

To get your basement bathroom in place as quickly, conveniently, and affordably as possible, hire a professional plumber to do the job. If you’re ready to add a bathroom to your finished basement, contact us at Black Diamond Plumbing & Mechanical.

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