Bathroom Installation Guide
A bathroom install is really a sequence of trades in the right order. Plan the layout and first-fix before anything is boarded, keep it Water-Regulations compliant, and the second-fix and finish fall into place.
A full bathroom installation is one of the larger jobs a plumber takes on, and the difference between a smooth fit and a fraught one is almost entirely down to sequence and planning. Pipework, waste positions and any structural or electrical work all have to be right before walls and floors are closed up, because putting them right afterwards means ripping tiling out.
This guide walks through the job in order: planning and setting out, first-fix pipework and waste, the compliance points under the Water Supply (Water Fittings) Regulations 1999, second-fix and connecting the sanitaryware, then testing, making good and pricing. It is written for the plumber coordinating the whole job, not just the plumbing lines.
Key takeaways
- Plan the layout, waste runs and first-fix before anything is boarded or tiled — mistakes are cheap now and expensive later.
- Set waste and soil connections with the correct falls first; supply pipework and isolation follow the fixed positions.
- Keep the installation Water-Regulations compliant — backflow protection, correct materials, and no cross-connection or contamination risk.
- Coordinate the electrics (zones, RCD, extract) with a competent electrician; bathroom electrical work is notifiable and zone-sensitive.
- Test and commission before final decoration — pressure-test supplies and check every waste before the room is finished.
Planning and setting out
Start with the layout, because everything downstream is fixed by it. Confirm the positions of the WC, basin, bath and shower against the available soil and waste connections and the falls those wastes need — moving a soil connection is far harder than moving a supply, so let the drainage lead the layout. Check floor and wall build-ups, access for pipe runs, and whether any joists need notching within permitted limits.
Agree the specification and layout with the customer in writing before you start, including the sanitaryware, so the first-fix positions are set once. Changes after first-fix are where bathroom jobs lose time and money.
First-fix: waste, supply and isolation
First-fix is the hidden pipework that gets buried or boarded. Run the soil and waste pipework to the fitting positions with correct, consistent falls and properly vented traps, then run the hot and cold supplies to each appliance, fitting isolation valves so every fitting can be shut off individually for second-fix and future maintenance.
Pressure-test the supply pipework at first-fix, before anything is closed in, so a weeping joint is found while it is still accessible. Clip and support everything properly — pipework that moves ticks, knocks and, at worst, works a joint loose behind a finished wall.
Test before you close it in
Pressure-test the supplies and check the wastes at first-fix. Finding a leak now is a quick fix; finding it after tiling means taking the wall back apart.
Doing this on a job? Job pricing calculator — part of TradePlanr. Free to start, no card needed.
Water-regulations compliance
A bathroom brings several Water Supply (Water Fittings) Regulations 1999 points together. Provide backflow protection appropriate to the risk — for example on a shower hose that can reach the pan or a bidet, and on any outside or utility connection off the same runs. Use WRAS-recognised fittings and materials, avoid any cross-connection between mains and stored water, and make sure overflows and warning pipes on any cisterns are correct.
Where the bathroom includes a scald-risk outlet such as a bath, Part G limits the hot water temperature at the bath to a maximum of around 44°C, typically achieved with a thermostatic mixing valve. Building compliance in as you first-fix is far easier than retro-fitting it.
Compliance is a first-fix decision
Backflow protection, a bath TMV for Part G, and WRAS fittings are much easier to build in at first-fix than to add after the room is tiled. Design them in from the start.
Second-fix and connecting the sanitaryware
With walls and floors finished, set and connect the sanitaryware: mount the WC and connect the pan and cistern, fit the basin and its trap, install the bath or shower and connect the mixer and waste, and set any TMV to the required blend temperature. Make each connection accessible where possible, seal around baths, trays and basins against the wall, and check every trap holds a water seal.
Fit and connect only after the tiling and sealing allow a clean, watertight junction — connecting sanitaryware to unfinished walls forces awkward re-work. Take care with silicone and sealing details; a neat, continuous seal is what stops water tracking behind the fittings.
Testing, making good and pricing
Commission the finished room: run every outlet, check for leaks at all connections, confirm the WC flushes and refills correctly, and verify each waste discharges and holds its seal with no smell of drains. Set and record any TMV commissioning, and demonstrate the controls to the customer.
For pricing, a bathroom is a multi-day, multi-stage job and should be priced as such — separate lines for strip-out, first-fix, any building or electrical work coordinated in, second-fix, and commissioning, rather than a single lump. That makes variations easy to price and shows the customer where the labour actually goes.
Build the quote in stages
Price a bathroom in TradePlanr as separate lines — strip-out, first-fix, second-fix, commissioning — so variations are simple to add and the accepted quote converts straight to an invoice.
From guidance to action
Frequently asked questions
What order do you install a bathroom in?
Plan and set out, then first-fix the waste and supply pipework and pressure-test it, then coordinate any building and electrical work, then finish the walls and floor, then second-fix and connect the sanitaryware, and finally test and commission. Sequence is everything — the hidden work must be right before the room is closed in.
What are the water-regulations points in a bathroom?
Provide backflow protection appropriate to the risk (for example on shower hoses and bidets), use WRAS-recognised fittings and materials, avoid cross-connection between mains and stored water, and get overflows correct. Where there is a bath, Part G limits the hot water there to around 44°C, usually via a TMV.
Who does the electrics in a bathroom installation?
A competent electrician. Bathroom electrical work is notifiable and zone-sensitive under BS 7671 and Part P, covering shaver points, extract fans, lighting, electric showers and heated rails. Coordinate the electrical first-fix with the plumbing first-fix so both are right before the room is boarded.
Related guides
How to Price a Bathroom Installation
A line-by-line way to price a full bathroom install — labour, materials, trades and margin.
Wet Room Installation Guide
Tanking, floor falls, drainage and waterproofing — how to build a wet room that never leaks.
TMV Installation & Commissioning Guide
Where TMVs are required, TMV2 vs TMV3, correct installation, and commissioning to the right blend temperature.
