A bathroom installation is the process of fitting and connecting the fixtures in a bathroom — the bath, basin, WC and shower — along with the pipework that supplies water and carries waste away. From the plumbing point of view, the job is really about two things: getting clean water to each fitting at a usable pressure, and getting wastewater away with a reliable fall. Almost every layout decision comes back to those two constraints, so it pays to understand them before you commit to a design.
Where to begin with a bathroom layout
Start with what cannot move easily. The single biggest fixed point is usually the soil pipe — the large pipe (typically 110mm) that takes waste from the WC. Moving it is possible but disruptive and often expensive, so most sensible layouts keep the WC close to where the soil stack already runs.
Once the WC position is roughly settled, the rest tends to follow. The basin and bath generate "grey" waste, which uses smaller pipes (32mm or 40mm) and is more forgiving about where it can run. A shower needs both a water supply and a waste outlet, plus a route for that waste to reach a stack or drain with enough downward slope.
It helps to think in terms of zones rather than precise positions at this stage. A few practical points worth weighing up:
- Group fittings together where you can. Clustering the WC, basin and bath shortens pipe runs and reduces the chance of waste flowing too slowly.
- Leave enough working space around each fitting. There are recommended clearances in front of a WC and basin; cramming them in looks fine on paper but feels tight in use.
- Check the floor build-up. A shower tray or wet room often needs the waste pipe to sit below floor level, which may mean lifting or building up the floor.
- Think about access for the future. A concealed cistern or a buried valve looks neat, but someone will eventually need to reach it.
This is also the right moment to settle the order of trades. A typical sequence is: first fix (running pipes and cables before walls are closed up), then tiling or boarding, then second fix (connecting the visible fittings). If a wet room is involved, tanking — the waterproofing layer — sits between the structural work and the tiling. Getting this sequence wrong is one of the more common causes of delay, because a trade that arrives early often has to leave and return.
Soil, waste and where fittings can realistically go
From the plumbing point of view, the job is really about two things: getting clean water to each fitting at a usable pressure, and getting wastewater away with a reliable fall.
The honest limit on where things can go is set by the waste pipes, not the supply. Water can be pushed almost anywhere through small pipes under modest pressure. Waste, by contrast, relies mostly on gravity, so the fall — the gentle downward slope of the pipe — is what decides whether a fitting will drain properly.
As a rough guide, waste pipes need a fall of around 1 in 40 (roughly 18mm to 22mm of drop per metre of run for the common pipe sizes). Too little fall and water sits in the pipe; too much and the water can race away, leaving solids behind. A WC waste, being larger, can run further than a basin waste before this becomes a problem, but every fitting has a practical maximum distance from the stack.
The soil pipe deserves particular attention because it carries the heaviest load. It connects to the soil stack, which is vented to the outside air — usually up through the roof — so that draining one fitting does not suck the water seals out of the others. Those water seals sit in the U-bend (the trap) beneath each fitting and stop drain smells coming back into the room. If you move a WC a long way from the stack, an extra vent or an air admittance valve may be needed to keep the seals intact.
When you are positioning a basin and WC, it is worth asking a few questions early:
- How far is each fitting from the existing stack, and can a proper fall be maintained over that distance?
- Does the waste route cross any joists, and if so, can they be drilled or notched safely without weakening the floor?
- Is there room for the trap beneath the basin, especially if it is wall-hung over a vanity unit?
- For a back-to-wall or wall-hung WC, is the supporting frame compatible with the wall and the soil connection behind it?
None of this rules out an ambitious layout. It simply means that the more a fitting moves away from the existing drainage, the more pipework, boxing-in and sometimes structural work the move quietly brings with it.
Getting enough pressure to the shower
A shower disappoints far more often through poor pressure and flow than through anything else, so it is worth pinning down the supply before choosing the shower itself. Pressure (how hard the water pushes) and flow rate (how much arrives per minute) are related but not the same; a shower needs both.
The right shower depends on the type of system supplying the house:
- A combi boiler takes water straight from the mains and heats it on demand. Mains pressure is usually decent, but flow can drop if several taps run at once, so a high-demand "rainfall" head may underperform.
- A gravity-fed system uses a cold tank in the loft and a hot cylinder. Pressure here depends on the height of the tank above the shower — the greater the height, the stronger the push. Low pressure is common on upper floors where there is little height to work with.
- An unvented cylinder stores hot water at mains pressure and tends to give strong, even flow to multiple outlets at once.
Where a gravity system gives weak pressure, a pump can be fitted to boost it, though pumps need a suitable supply and add noise and cost. An alternative is an electric shower, which heats cold mains water as it passes through, sidestepping the hot supply entirely — useful where hot-water pressure is the weak link.
Before settling on a shower, it is sensible to measure the actual flow at the relevant point rather than guess. A simple test — timing how long a container takes to fill from the supply — tells you more than the system type alone. Matching the shower to the measured supply avoids the common outcome of a handsome fitting that trickles.