Replacing a kitchen sink: inset, Belfast and what has to match

Changing a kitchen sink can be a quick swap or a small building job. The difference is almost always down to the worktop and the pipes underneath. This guide explains the main types of sink, the parts that come with them, and what has to match for a straight swap to work.

Types of kitchen sink

Inset (top-mounted) sinks. The most common type in UK kitchens. The sink drops into a hole cut in the worktop, and its rim sits on top, held by clips underneath and sealed to the worktop. Stainless steel, composite and ceramic inset sinks are all common.

Undermount sinks. Fixed underneath a solid worktop, such as stone or solid surface, so the worktop edge is exposed. The worktop has to be made for it, so this is usually decided when the worktop is ordered.

Belfast and butler sinks. Large, deep, fireclay sinks that sit on a base unit, with the front exposed. They are very heavy, need a unit designed to carry them, and the worktop is cut around them. They usually have no tap holes, so the tap goes in the worktop or on the wall. Some have an overflow slot, which needs a waste made for it.

Bowl choices. Single bowl, one and a half bowl (a main bowl and a small one for rinsing or a waste disposer) and double bowl, with or without a drainer, left- or right-handed. Larger bowls take bigger pans; a drainer takes worktop space. There is no right answer, but the bowl layout changes where the wastes and the trap sit.

Parts of a sink installation

• The waste. The outlet in each bowl, often a basket strainer waste with a removable basket.
• The overflow. A slot or hole near the top of the bowl, connected to the waste by a tube.
• The trap and waste kit. Under the sink, joining the bowls to one trap and the waste pipe. Many sink kits include a spigot for a washing machine or dishwasher drain hose.
• The tap. A monobloc mixer through a single hole, or older pillar taps through two. See mixer and bath taps for tap types, and boiling water taps if you want one.
• Tap connectors. Flexible connectors or copper tails joining the tap to the hot and cold supplies.
• Isolating valves on the hot and cold supplies, so the tap can be changed without turning off the whole house. See isolation valves.

What has to match for a straight swap

The worktop cut-out. A new inset sink needs a hole the right size. If the new sink is smaller than the old cut-out, its rim may not cover the hole. If it is larger, the hole has to be cut bigger, which is fine in laminate with the right tools but not something to attempt on stone. Measure the old sink and check the new sink's cut-out template before buying.

The base unit. The bowls have to fit inside the unit below, clear of its sides and any rails, and a Belfast sink needs a unit made for it.

The bowl and waste positions. If the new sink has its bowls the other way round, or its wastes in different places, the trap and waste pipe will need changing, and possibly the appliance connections.

The tap holes. A sink with no tap hole needs a hole drilled in the worktop. A sink with the wrong number of holes needs a different tap or a blanking cap.

The pipe positions. Hot and cold supplies that came up for old pillar taps may need re-routing for a new mixer.

If any of these do not match, it stops being a swap. That does not make it a big job, but it is the point where many people bring in a plumber or kitchen fitter.

Doing it carefully

• Turn the water off at the isolating valves or the stopcock, and open the tap to drain it.
• Have a bucket ready for the trap and towels for the cupboard.
• Check appliance connections under the sink. Dishwashers and washing machines often drain into the sink waste and take their water from valves nearby. See dishwasher plumbing and washing machine plumbing.
• Seal the rim as the sink maker says, usually with a supplied seal or a bead of silicone.
• Test everything by filling the bowls and letting them drain, running the tap, and watching under the sink with dry tissue for a few minutes.

Call a plumber or fitter if the supply pipes need moving, the worktop is stone or solid surface, the sink is a heavy fireclay one that needs a new unit, the waste pipe needs re-routing, or there is a food waste disposer involved (see waste disposal units).

A sink waste kit at Wickes

We haven't tested this. Figures are as the maker states them (checked 13 November 2026).

Can I put a Belfast sink in an ordinary kitchen unit?

Usually not without changes. Belfast and butler sinks are heavy and sit lower than an inset sink, so they need a base unit or frame designed for them and a worktop cut around them. Check the sink maker's requirements.

Do I need a new waste when I change the sink?

Usually, yes. Most new sinks come with their own wastes and overflow, and the old trap may not line up with the new bowl positions. A new trap kit is often the simplest route.

Why does my new sink leak at the waste?

Common causes are a waste washer that is missing, doubled or out of place, a joint that is not square, or an overflow tube that has not been pushed fully home. Dry it, run water into each bowl in turn, and watch to find the exact joint.