Plumbing for a Vanity Sink Unit


Arranging the plumbing for a vanity unit can involve considerable disruption, so it’s as well to get it out of the way and make good before the unit is installed.

It’s usually easier to lay on suitable hot and cold supplies before you do anything else. Run them as far as the proposed site of the unit, then fit stop-valves so that you can restore the household supply.

Running the waste pipe may be better left until the unit is installed so that you can ensure the correct fall. But as the proximity of the drains is likely to have a major influence on where you position the unit, it’s as well to think about it at the earliest possible stage.

Technically, you need permission from the local Building Control Office to install a new drain run. In practice you can probably get away with describing what you plan to do over the phone, or submitting a sketch plan — but be sure to check.

Plumbing in a vanity unit in a bathroom should be no more difficult than any other type of basin.

Hot and cold supplies can be run in 15mm pipe as far as the unit from the nearest suitable pipes, leaving the final connections to be made using flexible tap connectors.

Drainage can be via a bottle trap and 32mm (1-1/4″) plastic waste pipe so long as the run is no longer than 1.7m (6′ 6″); if it is, switch to the 40mm (1-1/2″) size. The pipe must have a slight fall, and you should avoid bends if possible. Fit access tees at bends which can’t be unblocked.

The waste can run into a hopper head, or to a single plastic stack via a connection boss.

Installing a vanity unit in a bedroom or other room can be trickier because of the absence of suitable pipes to connect to.

The cold supply should ideally be drinkable, which means on a tank fed system you need to take a branch directly from the rising main. Often the easiest connection point is in the loft, where the main enters the cold storage tank.

The hot supply can be branched off any suitable hot supply pipe, or from the main supply pipe at the hot water cylinder. An alternative is to fit an individual under-unit electric water heater.

It’s usually wise to select polybutylene plastic for both supply pipes, since this material is flexible enough to be threaded unobtrusively under floors, through hollow walls or along skirtings.

Drainage is likely to be the main problem unless the unit backs on to an outside wall near a stack; See Problem Solver below.

in the bathroomIn the bathroom, run the supplies from suitable pipes and connect the waste to a hopper or internal plastic stack; fit stopvalves and temporarily plug the waste.

in the bedroomIn a bedroom, run the cold from the rising main and the hot from the nearest suitable pipe. Connecting the waste may involve running the pipe under the floor.


Problem Solver

Non-bathroom drainage

Where there’s no connection point within close range, consider running the waste:

Under the floor

If the joists run in the right direction (the opposite way to the boards), you may be able to run the waste straight out to a stack or hopper head.

Check by lifting a board and looking through with a torch and mirror; if there are bracing pieces nailed between the joists, the job’s not on. Otherwise, simply make sure you use 40mm (1-1/2″) pipe if the run is over 1.7m (6′ 6″) long.

Through the wall

This is often overlooked, but if there’s a bathroom on the other side the Building Control Officer may allow you to run a 32mm (1-1/4″) waste into a larger pipe via a swept tee fitting.

26. May 2011 by admin
Categories: Plumbing, Sinks, Vanity Units | Tags: | Comments Off on Plumbing for a Vanity Sink Unit


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