How to Install a Bathroom Vanity from Scratch

Installing a new bathroom vanity is one of those projects that looks intimidating until you realize it's mostly about removing the old one and bolting down the new one. The plumbing side—connecting supply lines and the drain—isn't complicated if you understand how water gets in and waste gets out. The carpentry side is even simpler: get it level, get it tight to the wall, and make sure it's anchored so it won't shift when someone leans on it. The real satisfaction comes from seeing a tired, stained old sink cabinet disappear and a clean new one take its place. Done right, a vanity will sit solid and function flawlessly for fifteen years or more.

1. Shut Off Water First. Locate the shutoff valves under the sink and turn them clockwise until they stop. Turn on the faucet and let any remaining water drain out. If you can't find shutoff valves or they don't work, go to the main water shutoff for the house. This prevents a leak or spray when you disconnect the supply lines.
2. Disconnect Lines Methodically. Place a bucket under the supply line connections at the base of the faucet. Use an adjustable wrench to loosen the nuts where the hot and cold supply lines connect to the faucet tailpieces, turning counterclockwise. Once loose enough, finish unscrewing by hand. Then locate the P-trap under the sink—the curved section of pipe that holds water to block sewer gas. Loosen the slip nuts on both ends of the P-trap and remove it. Have towels ready; there will be water in there.
3. Free The Old Faucet. Go under the sink. You'll see the faucet is held down by a nut or clip on each side of the tailpiece, or sometimes by a mounting bracket. Use a basin wrench or adjustable wrench to unscrew these fasteners. The basin wrench is designed specifically for this tight space—if you don't have one, work slowly with an adjustable wrench, turning just a few degrees at a time. Once the fasteners are loose, the faucet will lift out from the top.
4. Muscle Out The Cabinet. Check if the vanity is screwed to the wall studs or just caulked in place. Look underneath the cabinet at the back—you'll usually see screws going through the hanging rail into the wall. Remove any screws you find. Loosen and break the caulk seal around the top edge with a caulk knife or putty knife. Then grasp the vanity on both sides, and pull it firmly away from the wall. It's heavy; if you're alone, get a second person. Check the floor for any remaining fasteners before you move it out of the room.
5. Reinforce Weak Walls. Look at the wall where the vanity hung. If you see studs or solid blocking behind where the vanity mounting rail was, you're good. If you see only drywall between studs in the area where the vanity will sit, you need to install a horizontal wood backer (blocking) behind the drywall. Cut a 2x10 or 2x12 to length, hold it level at the height where the vanity will mount (typically 30 to 34 inches up from the floor), and secure it to the studs with 3-inch screws. This gives you something solid to screw the vanity to.
6. Level It Perfectly. Slide the new vanity into place against the wall. Don't fasten it yet. Check that it's level from side to side using a level on top of the vanity. Check that it's level front to back as well. Adjust shims (thin wedges) under the feet if needed to get it level. Once level, check that the vanity sits flat against the wall with no gaps. If everything looks good, mark through the hanging rail or mounting holes where you'll screw it to the wall. You may need to drill through the drywall and into the blocking or studs.
7. Bolt It Down Solid. Drill pilot holes at the marks you made, then drive 2.5-inch wood screws (or the fasteners recommended by the vanity manufacturer) through the hanging rail into the studs or blocking. Use at least two screws, spaced as far apart as the vanity allows. Tighten firmly but don't overtighten—you want it snug to the wall, not crushed. Check once more that the vanity is level and flush.
8. Add Shutoff Control. Modern bathrooms should have shutoff valves close to the vanity so you don't have to access the main valve for future repairs. If yours are missing or if your lines come straight from the wall without valves, install them now. Shut off the water at the main. Unscrew the supply line where it enters the wall or the vanity cabinet. Wrap the male threads with plumber's tape and screw on an angle-stop valve. Turn it so the outlet points toward where your new faucet will be. Hand-tighten, then use a wrench for an extra quarter turn.
9. Connect Water Supply Lines. Position the new faucet so its tailpieces (the two copper stubs coming down from under the handle assembly) align with your supply lines. From underneath the vanity, push the supply line nuts onto the faucet tailpieces and tighten them with a wrench—hand-tight plus a quarter turn. Check above and below for drips. Turn the main shutoff back on slowly and check again. There should be no leaks at these connections.
10. Secure The Drain. The drain opening on the new vanity should be at a similar height to the old one, but confirm the new P-trap will fit without kinks. Dry-fit the P-trap first to make sure the pipes align. Once you're sure, hand-tighten the slip nuts at both ends of the P-trap. The nuts should be snug but not so tight that you can't unscrew them with a wrench later. Test by running water into the sink and watching for drips at the connections.
11. Test For Hidden Leaks. Fill the sink slowly and let the water drain out. Watch both supply line connections and the drain connections for any weeping or dripping. Let it run for a minute. Check again. Open the shut-off valves under the sink fully so water can flow freely. Run hot and cold water for thirty seconds and inspect the connections a final time. Place a bucket or tray under the P-trap and let the sink sit full for two minutes, then drain it. If there are no leaks, you're done with the water side.
12. Seal All Seams. Once you're confident there are no leaks, caulk around the perimeter where the vanity top meets the wall. Use 100% silicone or acrylic latex caulk, depending on your preference (silicone is more waterproof, latex is easier to paint). Cut the caulk tube at a 45-degree angle with a cutter or knife. Apply a thin, continuous bead along the seam. Smooth it with a wet finger or caulk tool. This seals out water from getting behind the vanity, which prevents rot.