Fitting a bathroom suite is one of the more ambitious DIY projects, but for a competent homeowner it is entirely achievable — particularly a like-for-like replacement where the pipe positions and waste connections are already established. Where it gets complicated is when you are moving sanitary ware, adding a new shower, or installing in a new space, all of which bring in more complex drainage and electrical considerations.
This guide covers the full process, from planning and regulatory compliance to the step-by-step installation of a bath, basin, and toilet.
Planning and Preparation
What You Need to Decide First
Before purchasing any sanitary ware, confirm:
- Existing waste positions — the soil stack connection point determines where your toilet can go (close-coupled toilets need to be within 6 m of the stack, with a fall of 1:80 minimum). Moving a toilet away from the existing soil connection adds significant cost.
- Water supply type — do you have mains-pressure hot and cold (combi boiler), or a stored hot water system (cylinder)? This determines which taps and shower fittings are compatible.
- Room size and Part M compliance — Building Regs Part M (accessibility) requires certain clearances around sanitary ware in new or substantially altered bathrooms. In particular, 700 mm clear in front of a WC pan and 600 mm to the side.
- Ventilation — Part F requires mechanical ventilation (minimum 15 l/s extract rate) in any bathroom without an openable window to outside. If you are adding a windowless en suite, a fan wired to the light circuit is required and is notifiable work under Part P.
Tools and Materials
| Item | Typical cost |
|---|---|
| Adjustable spanners × 2 | £18–£30 |
| Basin wrench | £15–£25 |
| Pipe cutter (15 mm, 22 mm) | £12–£20 |
| PTFE tape (3–4 rolls) | £3–£6 |
| Silicone sealant (sanitary grade) | £5–£10 per tube |
| Flexible tap connectors (× 4) | £8–£16 |
| Push-fit fittings, waste trap kits | £40–£80 |
| Water isolation valves (× 4 min.) | £12–£20 |
Step-by-Step: Fitting the Bath
1. Fit the Bath Legs and Frame
Assemble the bath frame (if a steel/acrylic bath with a pressed steel frame) on the floor, then invert the bath to attach the leg cradle with the supplied brackets. Adjust legs to the correct height — the bath rim should end up at approximately 520 mm above finished floor level.
2. Fit the Taps and Waste Before Installing the Bath
This is the most important advice for any bath installation: fit all taps, overflow, and waste trap assembly before the bath goes in. Lying on your back under a fitted bath to tighten tap backnuts is miserable. Fitting them on the floor with the bath accessible is straightforward.
- Fit tap tails into the holes with rubber gaskets and backnuts. Tighten firmly with a basin wrench — do not overtighten on acrylic or fibreglass; hand-tight plus a half turn is usually sufficient.
- Attach the overflow pipe and bath waste. Use plumber’s putty or the supplied rubber seal under the waste flange.
- Fit the trap (75 mm seal trap, 40 mm diameter waste outlet).
3. Position the Bath and Connect Waste
Slide the bath into position. The waste outlet must align with the existing 40 mm waste pipe in the floor or wall. Use flexible waste pipe if the alignment is not perfect — rigid ABS pipe requires exact positioning.
Connect the trap to the waste run with a slip-joint or push-fit fitting. Ensure there is a fall towards the drain (minimum 18 mm per metre for 40 mm horizontal waste runs under Part H of the Building Regs).
4. Connect the Water Supply
Turn off the water at the mains (or at the isolation valves if already fitted). Solder or push-fit new isolation valves into the existing hot and cold supplies. Connect flexible tap connectors from the isolation valves to the tap tails — these allow the tap to be independently isolated for future maintenance.
Turn the water on slowly and check for leaks at every connection.
5. Seal the Bath
Once the bath is in its final position and tiled (or panels fitted), apply a continuous bead of white sanitary silicone along the joint between the bath rim and the wall. Smooth with a wet finger or proprietary tool. Allow 24 hours before use.
Step-by-Step: Fitting the Toilet
WC Pan
- Position the pan over the soil pipe connection. For a close-coupled or back-to-wall toilet with a horizontal or bottom outlet, use a pan connector to mate the pan outlet to the 110 mm soil pipe.
- Mark the fixing holes. Drill into the floor (use appropriate fixings for concrete screed or timber floor). Do not overtighten — cracked WC pan bases are a common and expensive mistake.
- Push the pan connector onto the soil pipe outlet.
Cistern
For a close-coupled cistern:
- Drop the internal siphon/dual-flush mechanism into the cistern.
- Secure the cistern to the pan using the long bolts and rubber washers provided — rubber washers must seat correctly to prevent the cistern rocking (which will cause leaks).
- Connect the 15 mm cold water supply with an isolation valve and flexible connector to the bottom-entry or side-entry inlet valve.
Test flush several times and check all connections.
Step-by-Step: Fitting the Basin
- Fit taps and waste pop-up mechanism (if applicable) before mounting the basin.
- Fix the pedestal to the floor (1 screw through the back foot is usually sufficient for stability).
- Lower the basin onto the pedestal and check it sits level.
- Mark and fix the basin to the wall using the supplied screws and appropriate wall plugs.
- Connect waste trap (32 mm for basin) to existing waste pipe with push-fit fittings.
- Connect water supply with isolation valves and flexible connectors.
- Seal the joint between basin and wall with sanitary silicone.
Cost Summary
| Scenario | Typical cost (2026, inc. VAT) |
|---|---|
| DIY like-for-like suite replacement (materials only) | £350–£900 |
| Plumber labour, like-for-like replacement (2 days) | £600–£1,400 |
| Full bathroom renovation (suite + tiling + floor, plumber + tiler) | £4,500–£9,000 |
| Full bathroom renovation with new layout (moving soil stack) | £7,000–£14,000 |
What Requires a Professional
| Work | Qualification required |
|---|---|
| Mains water connections, pipework | Technically DIY-legal; Water Regs competency required; Water Regulations Advisory Scheme (WRAS) approval |
| New or relocated electrical circuits | Part P — qualified electrician only |
| Extractor fan wiring to light switch | Part P — qualified electrician only |
| Electric shower installation | Part P — qualified electrician only; also needs WRAS approval for water connections |
| Moving the soil stack connection | Best done by a qualified plumber; notifiable under Part H if creating a new drain connection |
Water supply work (fitting taps, connecting waste) is not notifiable under Part P or Part H for a like-for-like replacement in England. However, any new drainage connection to the public sewer system or on-site drainage system must be notified to Building Control under Part H.
