A bathroom refit is one of those jobs where the finished room looks simple, but the hidden work behind the tiles can decide the final bill. In London properties, especially Victorian and Edwardian conversions, we often find the real costs only appear once the old suite, tiles and boxing are removed.
For a sensible contingency, most homeowners should allow an extra £750-£3,500 on top of the quoted bathroom refit price. A small, modern flat with sound pipework may only need the lower end. A period house or rental flat with rotten flooring, outdated electrics or awkward soil pipework can quickly sit at the higher end.
The expensive mistake is spending the whole budget on tiles, brassware and sanitaryware, then having nothing left when the floor comes up wet or the electrics need bringing up to standard. That is when people cut corners, and bathrooms are not a good place to cut corners.
Why Bathroom Refit Costs Change Once the Room Is Stripped Out
Bathrooms hide faults well. Tiles can cover blown plaster, small leaks can run under vinyl for months, and boxed-in pipework may have been altered several times over the years. We have opened up bathrooms in Kensington and Chelsea where a neat-looking room had soft chipboard under the bath, corroded copper pipes in the floor void and old junction boxes too close to the shower area.
London housing stock adds its own complications. Many flats share communal soil stacks, older houses have uneven timber floors, and converted buildings often have pipe runs squeezed through old joists and tight risers. You cannot always see these issues during a first visit, even with a careful survey, because the faults are physically covered.
That is why a proper bathroom budget should include a contingency. Not because tradespeople cannot price a job, but because nobody should pretend they can see through walls, tiles and floors. A realistic allowance protects the quality of the job and avoids rushed decisions halfway through.
Set a Contingency Before Choosing Finishes
Before spending heavily on tiles and fittings, put aside 10-20% of the expected refit cost for hidden work. For a typical London bathroom refit costing £7,500-£17,000, that means keeping roughly £750-£3,500 available for surprises.
If the property is a newer flat with accessible services and a like-for-like layout, 10% may be enough. If it is a period conversion, a basement bathroom, a top-floor flat with shared drainage, or a rental property that has had several patch repairs, we would lean closer to 15-20%.
This money is not automatically spent. It is a safety margin for real faults such as leaking waste pipes, rotten subfloors, failed plaster, poor ventilation or electrical upgrades required for a compliant installation.
Strip Out Carefully and Check the Floor Structure
The first proper checkpoint is strip-out. Once the bath, shower tray, WC, basin, old tiles and flooring are removed, the floor and walls should be inspected before anything new goes in.
Common discoveries include water-damaged chipboard, loose floorboards around the WC, notched joists, and old leaks under the bath. Replacing a small section of subfloor might cost around £250-£600, while more involved timber repairs can run from £700-£1,800 if joists need attention or the room has to be strengthened for stone tiles or a large bath.
If the floor feels springy, smells damp, or shows dark staining around pipe penetrations, do not tile over it. Tiles and grout will not fix movement or rot. They will crack, loosen, and leave you paying twice.
Inspect Pipework Before Reusing It
Bathroom pipework often looks acceptable until it is disturbed. Old compression fittings, corroded copper, unsupported plastic waste pipes and poor falls on shower wastes are all common problems we see during refits.
A simple like-for-like pipe alteration may add £180-£450. Reworking multiple hot, cold and waste runs can add £600-£1,500, especially if pipes are buried in walls or floors. Moving a WC is usually more expensive because the soil pipe fall, route and connection into the stack have to be correct.
In many London flats, the soil stack is shared and cannot simply be cut or moved without care. If access is through another flat, a riser cupboard, or a communal area, the job may need coordination with the freeholder or managing agent.
For anything beyond a basic visible connection, use a qualified plumber. Kensington Maintenance Services Ltd handles this sort of work through our plumbing services, including fault finding, bathroom pipe alterations and leak repairs.
Check the Electrics Against Bathroom Safety Rules
Bathrooms are high-risk areas electrically because water and electrical fittings sit close together. Lighting, extractor fans, shaver points, electric underfloor heating and mirror cabinets all need to be suitable for their location in the room.
Electrical work in bathrooms must follow BS 7671 wiring requirements, and certain work is notifiable under Part P of the Building Regulations. RCD protection is normally expected, and fittings must be appropriate for the bathroom zones they are installed in.
Budget around £150-£350 for a small electrical alteration, £300-£750 for adding or relocating lighting and fan circuits, and £600-£1,500 if the bathroom wiring needs more extensive upgrading. If the consumer unit is old and lacks suitable RCD protection, costs can increase further after proper testing.
Do not DIY bathroom electrics. If old wiring, loose accessories, scorch marks, failed fans or unprotected circuits are found, stop and have the installation checked by a competent electrician. Our electrical services team can test, advise and carry out compliant bathroom work.
Allow for Wall Repairs, Tanking and Proper Preparation
Tiles are only as good as the surface behind them. We often remove tiles and find hollow plaster, old adhesive over paint, crumbly lath and plaster, or plasterboard that has softened around the shower.
Reboarding a shower area with suitable tile backer board can add £300-£900 depending on size. Tanking a wet area with a waterproof membrane system may add £250-£700, but it is money well spent around showers and baths. Retiling over weak or damp walls is false economy.
If you are fitting large-format tiles, the walls need to be flatter and stronger than they would for small ceramics. Uneven period walls may need extra preparation, which is not always obvious until the old finish comes off.
Test Ventilation Before Closing the Room Up
Poor ventilation is a common cause of peeling paint, mould, swollen timber and black spotting on silicone. In older London flats, bathrooms sometimes vent into an old duct, a ceiling void, or nowhere useful at all.
A basic replacement extractor fan may cost £120-£250 fitted if the wiring and ducting are suitable. A new fan with ducting, core drilling or roofline routing can add £350-£900. In flats, routes through external walls or communal parts may need permission before work starts.
Bathrooms without openable windows need reliable mechanical ventilation. Even with a window, a good timed or humidistat fan is often worthwhile, especially in rental properties where tenants may not ventilate the room consistently.
Price the Hidden Extras Before Ordering the Suite
Once the room has been assessed, firm up any extra work before expensive fixtures are ordered. This is the point to decide whether the WC is staying put, whether the shower valve can be recessed, whether the floor needs strengthening, and whether the lighting layout is safe and practical.
Typical hidden extras we advise budgeting for include:
-
Subfloor repairs: £250-£1,800 depending on damage and access.
-
Pipework changes: £180-£1,500 depending on how much is being moved.
-
Electrical upgrades: £150-£1,500 depending on testing and circuit condition.
-
Wall reboarding and tanking: £300-£1,200 for common bath or shower areas.
-
Improved extraction: £120-£900 depending on ducting route.
-
Making good and decorating outside the bathroom door: £150-£600 if plaster or paintwork is disturbed.
On landlord jobs, we also allow for tougher finishes and future access. A slightly larger access panel behind a concealed cistern can save a call-out later. A cheap concealed system with no access might look tidy on day one, but it is a nuisance when a flush valve fails.
Keep Records, Photos and Decisions in Writing
When unexpected work appears, ask for a clear explanation, photos where possible, and a written cost before it proceeds. A good tradesperson will not object to showing you the rotten board, leaking pipe or unsafe electrical fitting.
This is especially useful for landlords, leaseholders and property managers. Photos help justify service charge discussions, deposit decisions, insurance enquiries or freeholder permissions. They also give a record of pipe and cable routes before the walls are closed.
Keep invoices for plumbing and electrical work. For notifiable electrical work, make sure certification is provided where required. If gas pipework, a boiler flue route, or any gas appliance is affected by the bathroom layout, that must be dealt with by a Gas Safe registered engineer.
Plan Timing Around Access, Neighbours and Drying Times
A straightforward bathroom refit might take 7-12 working days, but hidden repairs can add several days. Timber repairs, plaster drying, tanking cure times and delayed freeholder approvals can all push the programme out.
In mansion blocks and converted flats, working hours may be restricted by the building rules. Parking suspensions, lift bookings, waste removal and neighbour access for shared pipework should be planned early. These are not glamorous parts of the job, but they keep the project moving.
Winter can also expose ventilation and damp problems more clearly. A bathroom that just about copes in July may show condensation, mould and slow drying in January when windows stay shut and heating cycles on and off.
Know When to Stop DIY and Call a Professional
Small cosmetic jobs, such as replacing a toilet seat, resealing sound edges or painting with bathroom-grade paint, may be suitable for a careful DIYer. But once you are into electrics, concealed plumbing, structural floor repairs, tanking or waste pipe alterations, it is time to bring in the right trade.
Call a professional if you find persistent damp, soft flooring, a leak below the bathroom, old or damaged wiring, cracked waste pipes, asbestos-suspect floor tiles, or anything connected to gas work. Asbestos-containing materials can be present in older floor tiles, adhesive, boxing boards and textured coatings, so do not sand, break or remove suspect materials without proper advice.
If you want one team to look at the whole room rather than juggling separate trades, Kensington Maintenance Services Ltd can coordinate plumbers, electricians, carpenters and decorators. For a clearer figure before you commit, you can get a quote and talk through the likely risks in your specific property.
Practical Tips for Keeping Bathroom Refit Surprises Under Control
Do not base your budget on showroom prices alone. Sanitaryware and tiles are only part of the job. Labour, preparation, waste disposal, waterproofing, pipework, electrics and making good often matter more to the final result.
Choose fittings that suit the property. Wall-hung WCs, concealed valves and flush-to-floor shower trays can look excellent, but they need proper structure, access and waterproofing. In older flats with shallow floors and awkward wastes, a simpler layout can be more reliable and cheaper to maintain.
Ask for allowances to be separated in the quote. For example, it helps to know what has been allowed for tiling, plumbing alterations, electrical work and wall preparation. If something hidden is found, you can see where the extra cost sits rather than feeling the whole price has become unclear.
Finally, keep some spare tiles. We usually suggest at least one unopened box if storage allows. If a concealed leak or future repair means a tile has to come off, matching a discontinued batch three years later can be surprisingly difficult.
Frequently Asked Questions
Q1: How much extra should I budget for unexpected costs in a bathroom refit?
For most London bathrooms, allow 10-20% extra, usually around £750-£3,500. Older properties, awkward flats and bathrooms with past leaks should sit toward the higher end.
Q2: What is the most common hidden cost during a bathroom refit?
Water damage around the bath, shower or WC is one of the most common. It often means replacing sections of subfloor, repairing walls or changing leaking pipework before the new suite can be fitted.
Q3: Can I keep costs down by leaving old pipework in place?
Sometimes, if it is sound, accessible and correctly installed. But reusing poor pipework behind new tiles is risky because a small leak later can mean removing finished surfaces.
Q4: Do bathroom electrics need a qualified electrician?
Yes, bathroom electrical work should be carried out by a competent electrician and must meet current safety requirements. Some work is notifiable under Part P of the Building Regulations.
Q5: Should a landlord spend more on a rental bathroom refit?
Not necessarily on luxury finishes, but it is worth spending on durable fittings, good extraction and proper access panels. Those choices usually reduce call-outs and water damage risk later.
The safest way to budget for a bathroom refit is to assume the visible room is not telling the whole story, then keep a sensible contingency for what may be behind the tiles, under the floor and inside the boxing. If you are planning a refit in Kensington, Chelsea or nearby London areas, our team at Kensington Maintenance Services Ltd can inspect the room, explain the likely risks plainly and carry out the plumbing, electrical, carpentry and finishing work properly from the start.