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How To Install a Bathroom Vanity and Sink

by Micheal Chotiner

When I was a cabinetmaker and general contractor 30 years ago, I learned how to fabricate a bathroom vanity and countertop from scratch, and also how to install them and hook up the plumbing. In those days, I even had to solder the copper water-supply fittings. Being a carpenter at heart, I have to admit there was a learning curve on the first few I did. If you're unsure about how to shut off the water supply to your bathroom or nervous about working with faucets and drains, you should work with a plumbing professional to remove an existing sink vanity and/or hook up a new sink.

Today, however, you can get a quality vanity cabinet with an integral sink for a couple hundred bucks. Most can even be assembled in less than an hour. With modern push-on and compression fittings, PVC pipe and simple trap parts, let's just say I don't miss those old days of soldering and tinkering around with complicated plumbing!

Get All the Right Parts

Bathroom vanity with sinkFirst, pick out a ready-to-assemble vanity cabinet, countertop and faucet. The countertop should be pre-drilled for the faucet and spout. If they don't come packaged with the faucet, you should also get water supply connectors with compression fittings at each end, matched in diameter to your faucet and the water supply lines serving the lavatory sink. You may also need a P-trap to connect the sink drain to the bathroom's branch drain line. There are various designs in plastic and metal with push-on or compression fittings, so pick the type that you're most comfortable working with.

Prepare the Space

You need to have hot and cold water supply lines and a connection to a drain line—three stubs protruding from the wall or floor—in a position where they can be enclosed by the vanity cabinet.

If you're replacing an existing sink vanity with a new one in more or less the same position, the plumbing you need is probably already in place. The water supply should have shutoff valves under the sink or nearby so you can turn off water to the lavatory faucet without cutting the supply to the whole house. Before you start working to remove the old vanity and sink, close these shutoff valves and open the faucet to make sure that the shutoffs still work. If you find that there's flow to the faucet after 20 seconds—even just a trickle—plan on replacing them with new quarter-turn shutoff valves.

If the existing shutoffs aren't working or absent, shut off the entire house's supply at the water main. Then, open the hot and cold faucet valves at a sink on the lowest point in the house. This will minimize dripping when you disconnect the water supply tubes at the sink you need to remove.

Disconnect the Existing Sink

Begin removal of the old sink and vanity by disconnecting the water supply tubes to the faucet and the P-trap from the drain. Place a large bowl or small bucket under the disconnection points to catch any water that may drip out in the process.

First, disconnect the P-trap from the sink-drain tailpiece to get it out of the way. You should be able to unscrew the compression nuts connecting it to the drainpipe stub and tailpiece with large Channellock pliers.

Disconnect p-trap from drain

In most baths installed after 1980, disconnecting the water supply should be a simple matter of unscrewing the tube fittings from the shutoff valves. Using a pipe wrench to hold the shutoff valve immobile, turn the compression nut at the end of the supply tube counter-clockwise. Repeat for both the hot and cold supply tubes.

Disconnect water supply from faucet

If you don't find shutoff valves and tubes with screw-type fittings, you're going to have to cut the copper tubes. It's best to use a mini-tubing cutter in a tight space like the inside of a vanity cabinet. Make sure that you leave enough of a stub so that you can install new shutoff valves later.

Using tubing cutter on copper pipe

Once the P-trap and water supply tubes have been disconnected, start looking at the underside of the vanity countertop to see how it's attached to the cabinet. This is usually done with either screws driven through mounting rails around the top of the cabinet or screw-type clamps. Loosen all of these screws and lift off the countertop, sink and all. If you don't find any hardware, the top may have been affixed to the cabinet with an adhesive. Run a sharp utility knife in the joint between the cabinet and countertop to break the bond, then lift off the top.

The old vanity cabinet is most likely fastened to the wall with screws through mounting rails at the top and bottom of the back. Remove all of the screws and pull the old vanity away from the wall. Maneuver it out of the bathroom so you've got plenty of room to work.

Spruce Up the Walls and Floor

Check the bathroom walls and floor for problems that would mar the debut of your newly installed vanity. Scrape off paint and caulk ridges left over from the old unit and determine whether the new vanity will cover the footprint of the old one. If new flooring is in the plan, finish the entire floor, even in the area that the vanity will rest on. If you're repainting the bathroom, do so before you install the sink unit. After all, would you bring a newborn baby home to an unfinished nursery?

Test-Fit the New Vanity

Before installing the permanent fixture, you need to see how the cabinet fits into place and to check whether there are any imperfections in the existing walls or floor that need to be addressed. Assemble the new vanity cabinet according to the manufacturer's instructions. Install the drawer glides and hinge mounts, but don't install the drawers or hang the doors yet. This will keep the cabinet light and easier to manage as you dry-fit it in place.

Place the cabinet as close as possible into its final position. Mark the back and/or bottom for holes that need to be cut for the pipes to enable the cabinet to be pushed flush to the wall. Make those cuts with a hole saw that's at least a quarter of an inch larger than the pipe diameters to allow some wiggle room for the final installation.

After making the cuts for the pipes, set the cabinet into position. Determine the location of wall studs behind the cabinet (and also to the side of the vanity if you're installing it in a corner). When fastening the vanity to the wall through mounting rails at the back, it's important to drive the screws into studs. If you don't have a stud finder, look closely at the drywall to detect an imperfectly finished seam—a sure sign that there's a stud behind it.

Once you've located at least one stud, measure to the left and right and try to determine whether the studs are spaced at 16 or 24 inches on center. Once you've got the stud layout and the vanity in position, make marks on the mounting rails aligned with the studs. You may wish to bore pilot holes for the screws at this point. Plan on using GRK structural screws no smaller than No. 10 x 2-1/2 in.—drywall screws would be inadequate. Depending on the width of the vanity, a total of four to six screws driven through the top and bottom mounting rails should be sufficient.

If you need to fasten the vanity to the wall through ceramic tile, drill pilot holes through the tile using a hammer drill and carbide-tipped masonry bit. It may be difficult to locate wall studs behind tile. In such a case, fasten the vanity with toggle bolts.

Level and Fasten the Vanity to the Wall

With the vanity dry-fitted in position, lay the countertop on it. Using a level, check the surface side-to-side and front to back. Insert shims under the base of the vanity if necessary to bring the cabinet and top into level position.. If your vanity has legs without adjustable feet, you may have to add them to level the cabinet.

With the cabinet and top shimmed level, check the countertop to see if it meets the wall evenly. Gaps of a quarter inch or less can be concealed later with a paintable siliconized latex caulk. If the gap is bigger than that, you may have to devise a better solution. Consider adding a tile backsplash or covering the gap with a molding.

Remove the countertop and set it aside. Again, check along the back of the cabinet to spot any gaps between it and the wall. If the wall is bowed or concave, insert shims in gaps that coincide with the studs into which you're planning to drive the fasteners. When you're sure that the cabinet is level and the gaps are shimmed, drive fasteners through the top and bottom rails to set it permanently.

Install the Doors and Drawers

With the cabinet fastened in place, assemble the drawers and slide them in next. Make sure they open and close easily without obstruction. Close all of the drawers and make sure their faces are flush in closed position. If you spot issues, it may be that you wracked or twisted the cabinet out of square when you fastened it to the wall. You may need to loosen some of the screws, re-shim and try again. If the reveals between the cabinet faces aren't even, you may be able to adjust the positions of the drawer glides to fix the appearance.

Once the drawers are in good working order, mount the doors. It's generally a simple matter to push the hinge arms onto the pre-installed mounts and fasten them with screws. Once the doors are fastened, close them and check the appearance. Do they close flush? Are the reveals even? If not, work with the adjustment screws on the hinge arms to move the doors in and out or left to right until you're satisfied.

Mount the faucet on the countertop... before installing the countertop!

It's easier to set up the faucet, pop-drain and water-supply connectors on the countertop before it's fastened to the vanity cabinet. Start by installing the faucet according to the manufacturer's instructions. It's usually just a matter of pressing some plumber's putty around the holes drilled in the counter, setting the faucet into the holes and securing it with a mounting plate and nuts on the underside of the counter. Once the faucet is set, install the pop-up drain. Again, prepare the hole in the basin with plumber's putty, insert the tailpiece in the hole and secure the assembly with a nut that tightens underneath the sink. Hook up the drain linkage according the manufacturer's instructions.

Wrap the threads of the hot and cold faucet feeds with plumber's tape, then thread on the water supply connector tubes. You're almost finished!

Place the Countertop on the Vanity

Since you test-fitted the countertop beforehand, you know how it will look when it's set in final position. Run a bead of silicone caulk around the top edge of the vanity cabinet, then pick up the countertop—sink fittings and all—and carefully set it in place on the cabinet. Double check the top for even overhangs at the cabinet sides. Adjust as necessary and let the adhesive set for about a day before using the sink or vanity for the first time.

That's it! Enjoy your brand new bathroom vanity and sink—you've earned it!

About the author:  Michael Chotiner, previously a carpenter and general contractor, writes for Home Decorators about installing bathroom and kitchen cabinets. To see a selection of bathroom vanities that you can use in your bathroom renovation, visit