A bathroom installation is the sequence of trades and plumbing decisions that turn an empty or stripped-out room into a working bathroom. In a typical fit-out a plumber, electrician, tiler and sometimes a plasterer each take a turn, working in a set order so that pipework and cabling are buried before surfaces go on. Understanding that order, and the choices made early on, is the difference between a job that runs smoothly and one that stalls.
Planning a new bathroom layout
Layout is decided first, because almost everything else follows from where the soil pipe and water supplies can reasonably go. The soil pipe — the large pipe that carries waste from the WC — is the hardest fixture to move, so most layouts are built around keeping the toilet close to it.
When planning positions, it helps to think about clearances and door swings. There should be space to stand in front of the basin, room to sit and stand at the WC, and a clear path into the shower or bath. A surveyor or fitter will usually measure the room and mark where each fixture lands before any pipework is committed.
Practical points worth settling at this stage include:
- Whether the bath stays or is replaced with a shower enclosure.
- Where the basin and WC sit relative to the existing waste runs.
- How much storage is wanted, and whether it is wall-hung or floor-standing.
- Whether walls need moving, which brings in building regulations and possibly structural advice.
The order the work happens in
A bathroom installation is the sequence of trades and plumbing decisions that turn an empty or stripped-out room into a working bathroom.
The work runs in two main phases: first fix and second fix. First fix is everything hidden in walls and floors; second fix is everything visible that connects to it.
A common sequence looks like this. The old bathroom is stripped out. Any wall changes or floor repairs are done. The plumber then carries out first-fix pipework, running hot and cold supplies and waste pipes to each fixture position. The electrician runs cables for lighting, an extractor fan, a shower if it is electric, and any heated towel rail or underfloor heating.
Once the hidden services are in, walls are made good and any backing boards go up. Waterproofing is applied where needed, then tiling follows. After tiling, second fix begins: the plumber connects the basin, WC, shower and taps, the electrician fits the lights, fan and switches, and the room is finished with sealant, trims and final adjustments. Each trade depends on the one before, so a slip in one stage tends to push the rest back.
Showers, pressure and pumps
The right shower depends on the water system in the property, so that is the first thing to check. A shower that performs well on one system can be weak or unusable on another.
There are three broad situations. A combination boiler heats water on demand and usually delivers a steady mains-pressure flow, which suits a mixer shower fed directly from the boiler. A gravity-fed system, with a cold tank in the loft and a hot cylinder, often gives lower pressure, and a pump may be added to lift the flow. An unvented cylinder stores hot water at mains pressure and generally supports a strong shower without a pump.
An electric shower is a separate case: it takes cold water only and heats it as it passes through, so it works regardless of the hot water system, though it needs its own electrical supply. Where pressure is genuinely low, a shower pump can boost it, but a pump must be fed correctly and cannot simply be added to a mains-pressure supply. A plumber will normally confirm the system type and flow rate before recommending a shower, rather than fitting one and hoping.
Waste, soil pipes and falls
Waste pipes only work if they fall the right way, so getting the gradient correct matters as much as the connections. A "fall" is the gentle downward slope that lets water and waste flow away under gravity.
Basin and bath wastes are smaller bore pipes, and they connect to a waste stack or run out to a soil pipe. Each fixture has a trap — the U-shaped bend that holds a plug of water to stop drain smells coming back into the room. Traps must stay full, which is why a run that is too long, too flat or too steep can cause gurgling or a dry trap.
The WC connects to the soil pipe, normally 110mm, usually with a flexible pan connector. Because the soil pipe is bulky and governed by the fall it needs, moving a toilet more than a short distance can mean boxing in new pipework or building up the floor, which is why the WC tends to anchor the layout. Where a fixture sits below the drain level or far from the stack, a small pump called a macerator can be used, though it has its own limitations and maintenance needs.
Waterproofing before tiling
Tiles and grout are not waterproof on their own, so the surfaces behind them have to be protected first. This is the step most often skimped, and it is the one that causes the worst problems later if it is missed.
In a shower or wet area, a tanking system is applied to the walls and any floor that will get wet. Tanking means sealing the surface with a waterproof membrane or liquid coating, paying particular attention to joints, corners and the points where pipes pass through. Standard plasterboard is a poor base for wet areas; water-resistant boards or dedicated tile backer boards are commonly used instead.
Once the waterproof layer is in place and any sealing tape at corners and floor junctions has cured, tiling can begin. The tile adhesive and grout add a further barrier, and the final defence is the flexible sealant run along the joints between tiles and fixtures, such as where the bath meets the wall. Done in this order, the bathroom resists the everyday soaking it will get; done out of order, water finds the gaps and works its way into the structure over time.