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While floor drains are usually thought of as a commercial plumbing drain, they also have some uses in residential homes (such as outside showers). In fact normal, stand-alone shower drains are technically floor drains, so the chances are you have one in your home.
Whether in commercial or residential application, floor drains have the same basic rules. We will talk about those in a minute. First let’s address a fairly common confusion.
One important note here – this article pertains to floor drains used to collect waste water, not groundwater. Groundwater drains have some different rules that are not covered in this article.
Floor Drain vs Floor Sink
A floor drain should not be confused with a floor sink. A floor drain is meant as a “direct” waste drain. It is used to drain whatever water winds up on the floor. In the shower, it drains the water that is on the shower floor while showering. In a commercial restroom is it used to drain water spilled on the floor, or water used to clean the bathroom. They function similarly in other applications.
A floor sink is part of an “indirect” waste system. An example of this is a commercial sink. The waste water from the sink goes down the sink drain, via the waste pipes, where it is dumped into a floor sink. Simply put, a floor drain is a drain sitting in the floor. A floor sink kind of looks like a square, porcelain sink, set in the floor.
Rules about Floor Drains
Now that that is out of the way, there are a few things regarding floor drains that you may want to know.
The first is that they are usually 2” in diameter in residential and light commercial applications, although there much bigger ones used for other commercial applications.
The second thing to know is that they are one of the few plumbing drains where the proper access point to clean them is directly through the drain, although having an accessible cleanout is often better, if available.
Like other fixture drains, floor drains must have a p-trap, and must be properly vented. As is can be sometimes difficult to vent some commercial floor drains, there are more creative ways to vent them, but they still must be vented to code.
Something else that comes up quite often is the potential for the trap to dry out. Floor drains need to get enough water in them to keep the water in the trap from going stagnant, or drying out. Stagnant water smells bad and breeds bacteria. If the trap dries out, the sewer gasses will escape into the room. That smells even worse and is very unhealthy, not to mention dangerous (sewer gas contains methane).
In order to prevent these from happening, the plumbing code requires a “p-trap primer” to be installed. This is basically a fitting that activates regularly to add water into the p-trap. It is most commonly done via a valve near a toilet or other fixture that uses a sudden drop of pressure to activate, sending a small amount of water into the trap.
While that works really well in a commercial setting, most homes do not have a p-trap primer for the shower drain. That being the case, if you have a standalone shower that you do not use regularly, you should still regularly turn the shower on to make sure your shower trap does not run dry or go stagnant. Even if it is once a week for a few minutes, that is better than nothing.
Do you have more questions about floor drains, or need one serviced or installed? Give Gogo Rooter Plumbing a call. We can help.