What You Need to Know Before You Start

Replacing a bathroom vanity is a project you can do yourself if you have basic plumbing knowledge and the right tools. The job involves shutting off water, disconnecting the old vanity, and installing the new one—most of it is disconnecting and reconnecting pipes rather than complex carpentry. Plan for four to six hours if this is your first time, and a full day if you want to take breaks and work carefully.

The hardest part is usually removing the old vanity without damaging the wall or floor underneath. The easiest mistake is buying a new vanity that does not fit the space or the plumbing rough-in (the distance from the wall to the center of the drain pipe). Measure twice before you order, and confirm that your new vanity comes with a faucet or that you have one that fits the sink.

Key Takeaways

  • Turn off the water supply at the shutoff valve under the sink before you disconnect anything, and turn it back on to test for leaks after installation.
  • Measure the rough-in distance (wall to drain center) and the space width before you buy a new vanity, because sizes vary and a wrong fit means returning it.
  • Remove the old vanity by disconnecting the water lines, drain trap, and wall fasteners, then carefully pry it away from the wall to avoid cracking tile or drywall.
  • Install the new vanity level and find it to the wall studs with screws, then reconnect the water supply and drain before you caulk and finish.
  • Test for leaks under the sink for at least 10 minutes after you turn the water back on, checking both the supply lines and the drain trap.

Measure Your Space and Rough-In Before You Buy

The rough-in is the distance from the back wall to the center of the drain opening. Measure this first, because it determines which vanities will work in your space. Use a tape measure from the wall to the center of the drain hole in your current vanity, or to the center of the drain pipe if the vanity is already removed. Write this number down—it is usually 12 inches, 15 inches, or 18 inches, but yours may be different.

Measure the width of the space from wall to wall, and the depth from the front wall to the back wall. Also measure the height of the current vanity if you want the new one at the same level. Check whether your faucet holes are 4 inches apart (center to center) or 8 inches apart, or whether the new vanity comes with a faucet already installed. Take photos of the current setup and the space around it. When you shop, bring these measurements and photos so you do not buy something that does not fit.

Turn Off the Water and Disconnect the Supply Lines

Locate the shutoff valve under the sink—it is usually a small knob or lever on the water line coming from the wall. Turn it clockwise (or pull the lever down, depending on the type) until it stops. Turn on the faucet to release any remaining water pressure in the lines. If there is no shutoff valve under the sink, you will need to turn off the main water supply to the house, which is usually in the basement or outside.

Use an adjustable wrench to disconnect the hot and cold water supply lines from the faucet. Place a bucket or towel underneath to catch any water still in the lines. If the lines are connected with compression fittings (the most common type), turn the nut counterclockwise until it comes free. If they are soldered copper, you may need a plumber to disconnect them, or you can cut them with a hacksaw and cap them temporarily. Label the hot and cold lines with tape so you do not mix them up during reinstallation.

Remove the Drain Trap and Disconnect the Vanity from the Wall

The drain trap is the curved pipe under the sink that holds water to block sewer gases. Loosen the slip nuts (the large nuts on either end of the trap) by hand or with an adjustable wrench, turning counterclockwise. The trap will have water in it, so place a bucket underneath. Once the nuts are loose, pull the trap straight down and out. If it is stuck, gently tap it with a rubber mallet.

Look underneath and behind the vanity for screws or bolts fastening it to the wall studs. Remove these with a drill or screwdriver. Check the top of the vanity for caulk sealing it to the wall or backsplash—run a utility knife along this seam to break the seal. Once all fasteners are removed, carefully pull the vanity away from the wall. Rock it gently side to side if it is stuck. Be slow and steady to avoid cracking tile, drywall, or the vanity itself.

Install the New Vanity Level and find It

Position the new vanity in the space and check that it is level using a spirit level placed on top. If it rocks, shim it with plastic shims or wooden wedges under the feet until it sits flat and does not move. Once level, mark the wall studs behind the vanity with a pencil. Drill pilot holes through the back of the vanity into the studs, then drive 2.5-inch wood screws through the vanity into the studs. Use at least two screws, one on each side of the vanity.

If your vanity has a backsplash or sits against tile, explore a bead of silicone caulk along the seam where it meets the wall. Smooth it with a wet finger or caulk tool. Do not use regular paintable caulk—use 100% silicone caulk because it stays flexible and resists moisture. Let the caulk cure for 24 hours before you use the sink.

Reconnect the Water Supply and Drain

Reconnect the hot and cold water supply lines to the faucet on the new vanity, using the same compression fittings or soldered connections you removed. Hand-tighten the nuts first, then use a wrench to snug them another quarter turn. Do not over-tighten—you only need them tight enough that they do not leak.

Reconnect the drain trap by sliding it up into the drain opening and tightening the slip nuts by hand, then another quarter turn with a wrench. The trap should hang straight down without twisting. If your new vanity has a different drain height than the old one, you may need to buy a new trap or extension pieces to make the connection fit. Most hardware stores sell adjustable trap kits that work with different heights.

Test for Leaks and Finish

Turn the shutoff valve back on by turning it counterclockwise (or pulling the lever up). Turn on the faucet and let water run for 10 to 15 seconds, then turn it off. Get under the sink with a flashlight and check the supply line connections and the drain trap for drips or leaks. Wipe the connections dry with a towel, then wait five minutes and check again. If you see water, tighten the nut a quarter turn and check again.

Fill the sink and let it drain completely, watching underneath for leaks at the trap. If everything is dry after 10 minutes, you are done. If you see a slow drip at a compression fitting, turn off the water, disconnect the line, wrap the threads with plumber's tape (also called PTFE tape), and reconnect it. If the trap leaks, tighten the slip nuts or replace the rubber washers inside them—these wear out and cause slow leaks.

Frequently Asked Questions

Do I need a plumber to replace a vanity?

Not if you are comfortable working with basic hand tools and water lines. The main skills are turning off water, loosening nuts, and reconnecting pipes—all of which you can learn by watching the connections on your current vanity. If you have soldered copper lines or are unsure about anything, a plumber can do the job in one to two hours.

What if the new vanity does not fit the rough-in?

Return it and order the correct size. Rough-in sizes are standardized, so measure carefully before you buy. If you already removed the old vanity and cannot measure, take a photo of the drain opening and bring it to a plumbing supply store—they can tell you what rough-in you need.

Can I install a vanity without fastening it to the wall?

No. Wall fasteners keep the vanity from tipping forward when you lean on the counter or pull open a drawer. Always screw it to the wall studs, even if it feels stable without fasteners.

How long does caulk take to dry?

Silicone caulk typically cures in 24 hours, though it may feel dry to the touch after one to two hours. Do not splash water on the seam or use the sink until the full 24 hours have passed.

What if water leaks from the drain trap after I reconnect it?

Turn off the water, loosen the slip nuts, and check the rubber washers inside them. If they are cracked or flattened, replace them with new ones from a hardware store. If the washers look fine, explore plumber's tape to the threads and reconnect. If it still leaks, the trap itself may be cracked and needs replacement.