How To Rough In a Double Sink Vanity

You’ve seen them, no doubt.  Maybe, you even have one or grew up in a household that had one.  A double sink vanity, a vanity with two sinks instead of the customary one,  is a true luxury no matter the house’s population.

In a family of seven children, for instance, all in school at the same time, it was an essential luxury.  Otherwise, busses were missed.

Two sinks, but not necessarily two full sets of plumbing needs, define a double sink vanity.  Supply and drain pipes can serve double duty using tee fittings, special valves, extension pipes, 90 degree elbows, and hoses.

As with all plumbing projects, though, you need to consult the local regulations and discuss your plans with the local plumbing inspector.  You can avoid having to rip something out and start all over again by a quick chat with the inspector.

Let’s examine the process.

What is Rough In Plumbing?

A plumbing rough in refers to boring the holes in framing studs and flooring through which all water supply and drain pipes will run, both up and down.  Then, all pipe connections are made either to feed into or take from the plumbing fixture.

The “rough” in “rough in” refers to the fact that the pipes dead end in the lower part of the wall, the part that will be behind the vanity cabinet doors.  No sink, faucet, or other fixture has been connected to them yet.  They are unfinished.

All of the plumbing will be enclosed in that vanity cabinet, just as the plumbing for a single sink vanity is beneath the sink and enclosed.  The vanity is obviously large enough to accommodate two sinks, so it is also large enough to accommodate all of their plumbing –  –  the fittings, valves, elbows, and hoses.

Some  Considerations for Double Sink Vanities and Plumbing

Sinks in a double sink configuration should be spaced at least 30 inches apart, but probably closer to 36 inches, measured center of sink to center of sink.  You want to have enough elbow room while you’re sharing with another person.

This allows plenty of room beneath the sink for the plumbing needed to feed water to and drain it from each sink, too.

Bathroom Sink Materials

Bathroom Sinks

Materials for bathrooms are plentiful to choose from and varied in styles.  A double sink configuration will often come in a single vanity top, eliminating the need to measure spacing between the sinks.

Among your choices for materials:

  • Ceramics, strong surfaces that are scratch and chip resistant
  • Porcelain, durable, soft in appearance, easy to clean
  • Stone – granite, marble, sandstone, onyx – porous and needing special care, but making a stunning appearance as a work of art
  • Stainless steel, a bit boring by comparison, but easy to clean and germ-resistant
  • Wood, usually teak, sometimes bamboo
  • Resin, durable, and easy to clean

Each makes its own statement in a double sink vanity, adding color, class, and distinction to your bathroom.

Plumbing Needs

Every sink has a drain line that carries out the waste-water, and the pipe must have a trap to seal the drain.  This will be common to all sink plumbing needs.

The seal is required to prevent sewer gasses from rising up into the bathroom.  In fact, every fixture that drains connects to a pipe that has such a trap..

Additionally, every sink requires a sink vent in order to function correctly. A vent helps equalize the pressure on a drain pipe as the water flows down to ensure that the flow is smooth and steady.

These needs, however, are common for all bathroom sinks, single or double.  When local plumbing regulations permit a shared drain, though, there is no double expense.

Helpful Plumbing Instructions

As always, YouTube can provide a variety of videos to watch on just about any subject, including double vanity sinks.

We mentioned above a shared drainage pipe for a double sink vanity.  Here’s a video to show what this looks like:

You’ll also see a second rough plumbing drain configuration in this video, as the plumber discusses different local plumbing regulations.  It’s worth a watch.

For a much more comprehensive video of roughing in a double sink vanity, you might want to watch these two videos:

It’s a two-parter, and it’s a few years old now, but it shows the process of the roughing in.


You need the extra space, yes.  Whether for yourself or other household members, that extra space of a double sink sure is convenient. 

But they also will add value to your home.  The typical bathroom will have a single sink vanity, so yours, with a double sink, will stand out and become more attractive to potential buyers when you decide to sell.  “His” and “Hers” sinks can go a long way to making a sale happen.

They also can go a long way to making your bathroom life much easier.

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