Fitting a new bathroom runs in a set order: strip out the old room, do the first-fix plumbing and electrics inside the walls and floor, board and tile, then second-fix the visible fittings before a final seal. The plumbing decisions that matter most are made early, while pipes are still exposed — once tiles go on, moving a waste or a valve means starting again. A straightforward swap might take a week to ten days; a full reconfiguration takes longer.
The order a bathroom comes together in
A bathroom is built in stages, and each one depends on the last being right. Rushing or reordering them is where problems and extra cost creep in.
- Strip-out: the old suite, tiles and sometimes flooring come out, exposing the pipework and wall surfaces.
- First fix: the hidden work — running hot and cold supply pipes, waste pipes, and any electrical cabling for lights, fans and shavers. This happens before walls are closed up.
- Boarding and preparation: walls are made good, often with moisture-resistant or waterproof backer board in wet areas, and floors are levelled.
- Tiling: walls and floors are tiled and grouted once everything behind them is fixed in place.
- Second fix: the visible fittings — taps, the shower, the toilet, the basin and any heated towel rail — are connected to the pipes left waiting at first fix.
- Final seal and finish: silicone sealant around the bath, tray, basin and tiled junctions, plus any last decorating.
The sequence matters because tiling locks the layout in. A fitter normally wants the suite chosen and on site before first fix, so pipes land exactly where the new fittings need them.
First-fix decisions you can't easily undo later
The plumbing decisions that matter most are made early, while pipes are still exposed — once tiles go on, moving a waste or a valve means starting again.
First-fix plumbing is the stage that sets the bathroom's bones. It is the rough-in work — the supply and waste pipes buried in walls, floors and ceilings — and it is far cheaper to get right now than to revisit once tiles are down.
The choices that lock in here include where the basin, toilet, bath and shower sit, and therefore where every pipe must run. Moving a toilet, for instance, means relocating the soil pipe, which is rarely simple. The position of a shower valve, the height of a basin and the type of flushing system all need confirming before pipes are chased into the walls.
It is also worth thinking about future maintenance at this stage. A reader planning the room should ask whether isolation valves are being fitted on each supply, so individual fittings can be turned off later without draining the whole system. Once everything is tiled and sealed, access is limited, so anything that might need servicing benefits from being reachable.
Showers, baths and getting the waste falls right
The shower valve is the heart of a shower, and the type chosen shapes the first-fix work. A concealed (built-in) valve sits inside the wall and needs its pipework set to a precise depth before tiling; an exposed valve sits on the wall surface and is more forgiving. Mixer valves blend hot and cold, while thermostatic ones hold a steady temperature even if water is drawn elsewhere in the house — a common choice for safety and comfort.
Water pressure decides what a shower can deliver. A gravity-fed system from a cold tank in the loft gives lower pressure than a combi boiler or an unvented cylinder, so the valve and showerhead need matching to the supply. A pump may be added where pressure is weak, but it has to suit the system.
Waste falls are the quiet detail that makes or breaks a bathroom. Every waste — from the basin, bath, shower and toilet — relies on a slight downward slope so water and waste flow away by gravity. Too shallow a fall and water sits and drains slowly; too steep and water can race ahead of solids, leaving blockages.
Waste traps sit beneath each fitting. A trap is the curved or bottle-shaped section that holds a small plug of water, blocking drain smells from rising into the room. Shower trays in particular need enough height beneath them to fit a trap with a proper fall, which is why tray and floor build-up are planned early. A trap that is too shallow or wrongly installed is a frequent cause of slow draining and odour.
Sealing, tiling and a watertight finish
Tiling and sealing are what keep water where it belongs. Behind the tiles, wet areas — especially inside a shower enclosure — are often tanked, meaning a waterproof membrane or coating is applied so that any water passing through grout cannot reach the wall structure. This is invisible once finished but does much of the protective work.
Tiles are bedded on adhesive and the gaps filled with grout. Grout resists water but is not fully waterproof, which is why the membrane behind it matters and why corners and edges are handled differently. Where two surfaces meet — the bath against the wall, the tray against the tiles, the basin against its splashback — a flexible silicone sealant is used rather than grout, because these joints move slightly and rigid grout would crack.
The final seal is the last job for good reason. Silicone needs clean, dry surfaces and time to cure before the bath or shower is used. A neat, continuous bead with no gaps is what stops slow leaks that might otherwise go unnoticed until they reach the room below.
What shapes the cost and the timeline
Two bathrooms of the same size can cost very differently. The biggest variables are how much the layout changes and what lies behind the walls.
- Moving fittings: keeping the toilet, basin and bath in their existing spots is far cheaper than relocating them, because the waste and supply runs stay put.
- System condition: old or corroded pipework found during strip-out may need replacing, adding time and cost.
- Tiling extent: fully tiled walls take longer than part-tiling, and large-format or patterned tiles are slower to lay.
- Fittings chosen: the suite, shower valve and finishes vary widely in price and in how much fitting work they need.
- Trades involved: a job needing a plumber, tiler and electrician must coordinate around each other's stages, which affects the schedule.
A timeline also depends on drying and curing time — adhesive, grout and silicone each need to set, and these waits are built into the plan rather than skipped. Anyone comparing quotes should check what is included, whether the existing pipework has been assessed, and how the stages are sequenced, since that detail explains most of the difference between one estimate and another.
Last reviewed: June 2026