How to Install a Bathroom Vanity Unit: Choice, Levelling and Connections Explained

The vanity unit is both a storage piece and the pedestal for the basin or sink. Its installation requires method: levelling, fixing to the wall, cutting out for the plumbing connections and connecting the trap. It is an operation within the reach of a careful DIYer, which brings a real gain in comfort and aesthetics to the bathroom. Allow half a day for the installation and a budget of 80 to 400 euros depending on the model.

Choosing the right unit

• The wall-mounted unit: fixed to the wall, it frees up the floor and makes cleaning easier, ideal in small bathrooms
• The unit on legs: simple to install, stable, with or without a niche for the trap
• The finishes: wood veneer, lacquered, moisture-resistant melamine panels, or resin
• The size: from 40 to 80 cm wide, to be chosen according to the basin and the available space
• The column or integrated storage unit, which offers shelves or a drawer

Before buying, measure the width available between the walls and the depth of the space under the basin. Also check the position of the water supplies and the drain outlet on the wall: some units require back cutouts to let the fittings through, while others have a removable base panel for easy access. For a wall-mounted unit, make sure the wall is strong enough (concrete, block or timber frame) and locate the studs if you are on plasterboard, because fixing into the cavity of the partition is fragile.

The tools and materials you need

• Spirit level, tape measure, pencil and straightedge
• Drill with bits suited to the support and wall plugs
• Screwdriver, screwdriver/drill driver and adjustable wrench
• Jigsaw if you need to cut the base of the unit for the connections
• Neutral silicone and plumber's mastic for sealing the joints
• PTFE tape for the threads and sealing gaskets

Installing the unit step by step

1. Turn off the hot and cold water supplies, then open the tap to drain the pipes.
2. Remove the old unit or clear the space, disconnecting the trap and the flexible hoses.
3. Position the new unit against the wall and check its level in both directions.
4. Mark the fixing points in pencil through the pre-drilled holes or the mounting bracket.
5. Drill, insert the wall plugs, then screw the unit starting at the top without tightening fully.
6. Adjust the legs or packers, then tighten the fixings definitively.
7. Cut the base if necessary for the passage of the supplies and the drain, keeping access to the trap.
8. Connect the trap and the water hoses, open the valves and check for leaks.

Connecting the drain and the water supplies

The connection follows the principle of all sanitary plumbing: cold water, hot water and a drain. Connect the supply hoses onto the shut-off valves positioning the gaskets correctly, then connect the trap to the drain outlet respecting the slope and avoiding kinks. If the unit has a connection column, follow the manufacturer's instructions for the orientation of the pipes. Then open the valves slowly and check every joint: a badly positioned gasket or excessive tightening is the most common cause of leaks.

The mistakes to avoid

• Drilling the tiles at the location of a chip or a corner, which cracks the tile
• Tightening the wall plugs to the point of splitting the unit panel
• Forgetting to drain the pipes before removal, which leaves residual water in the unit
• Cutting a passage that is too small for the connections, making the trap inaccessible
• Installing a unit out of level, which makes the doors hang crooked

Installing a vanity unit turns a functional bathroom into an organised, pleasant room. The main difficulty is not installing the unit itself, but connecting the tapware and trap cleanly: if you have never touched plumbing, entrust that part to a professional while installing the unit yourself. With a well-marked wall, careful levelling and correctly tightened connections, your unit will last for years without a problem.