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Plumbing a Basement Bathroom

Plumbing a bathroom in the basement is more complex than adding one elsewhere in the home — you have to cut through the concrete floor, and you have gravity working against you. Consider these tips from master plumbers to help ensure your next basement bathroom installation goes smoothly.

With more homeowners looking for ways to add value to their homes, many plan to remodel their unfinished basements — and adding an extra bathroom is usually central to those plans. A new basement bathroom is a lot easier for the homeowner to visualize, however, than for a plumber to install. 

Plumbing a basement bathroom can be time consuming and expensive, but for an experienced plumber, it’s also straightforward. Here are a few of the potential problem areas, along with tips from experts on how to do the job well. 

Find the Sewer Line

Gravity usually isn’t on your side when building a basement bathroom. In many cases, you’ll need an ejector to transport waste away from the bathroom. However, sometimes the sewage lines will be far enough below the floor to allow you to plumb the bathroom without an ejector. (This is also dependent on local building codes, of course.) You can gauge the position of a sewage line by using a locator. Also, make sure the drainage lines are at least four inches in diameter for toilet and shower lines. 

Excavation and Sewage Ejector Pump Installation 

If the underground sewage line won’t work, you’ll need to excavate in order to dig the pit for the sewage ejector pump. The good news here is that concrete basement floors aren’t very thick. You can cut through them with an electric jackhammer or saw. Before you make any cuts, though, make sure you are equipped to handle the concrete dust.

“That dust goes through the house something fierce,” says Mick Gage, owner of Mick Gage Plumbing and Heating in New Hampton, Iowa. “We build a plastic wall around the area, get a fan going, and blow the dust right out the side of the house through a basement window.” 

Choose the Right Plumbing Pipe

When it comes to installing pipe, different municipalities have different preferences for material. But for Gage, there’s no question: PVC is best.

“Cast-iron pipe has pores, and over time acid will eat the bottom right out of the pipe,” Gage says. “But the plastic will stand up.” 

Backfill and Sump Pump

Next comes backfilling the area you have excavated. It may seem intuitive to fill the gaps with the same dirt you pulled out in the first place, but that’s the wrong move. 

“You’re never going to compact [the original soil] the way Mother Nature had it before you went in,” says Bill Flader, owner of Flader Plumbing and Heating Co. in Evanston, Ill. “Even if you stomp on it and beat it down with a tamper, in six months or a year, after a few rainfalls and after the groundwater table rises and falls, that ground is going to settle and you’re going to have a void under the basement floor, which then can be a source for cracks.”

Instead, Flader recommends using gravel, which allows groundwater room to seep without putting pressure on the floor. He suggests adding a sump pump (if there’s not already one in the basement) for the same reason: A sump pump can protect the home from flooding and also can prevent cracks from developing in the concrete patching.

“The sump pump takes in groundwater and helps keep the water table lower,” Flader says.

Plumbing a basement bathroom can be a big job, but it’s not complicated once you understand its unique challenges. And that means more business for you, as more of your customers see their dream of a finished basement become a reality.


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