Bathroom renovation: cost of a bathroom and wet-room core renovation 2026

Many bathroom renovations take place in flats in older blocks, often built of concrete or prefabricated panels. In some of these buildings the original bathroom is a prefabricated pod made of laminate boards or thin panels with tiles. It has lasted for decades, but it is low, hard to clean, and the shared risers for water, drainage and sometimes gas run right behind it. Once the pod or the old partitions come out, new walls go up and you can partly change the layout. People often combine the bathroom and WC or move the door.

Be careful with the walls around it, though. In a block of flats, the external walls and the walls between flats are usually load-bearing. Do not chase into them or widen openings without a structural engineer's assessment. The pod or light partitions are not load-bearing, but the work happens right next to services that belong to the whole building. Some older buildings also have risers, vent pipes or boxing made of asbestos cement. If you suspect asbestos, leave it alone. Only a licensed asbestos contractor should remove it.

Before you start, tell the building management or owners' association and agree a date for shutting off the water in the riser. Whether your work needs a notification, a permit or nothing at all depends on local building regulations. Check this directly with your local building authority rather than assuming that a quick notice is enough. If you smell gas during demolition, stop work at once, open the windows, do not touch any electrical switches and call the gas emergency line or 112. Only a qualified, registered gas engineer may work on gas pipes.

In brick flats and houses, the bathroom usually has masonry walls, and the renovation starts with stripping the wall and floor tiles. Common surprises include old galvanised steel pipes furred up with limescale, cast-iron drainage and walls that are out of true and need levelling before tiling. In very old houses you may even find lead water pipes, which should be replaced. A house does give you more freedom in routing the waste pipes, so a level-access shower is usually easier to build there.

In a bathroom of around 4 to 5 m², the first decision is simple: bath or shower? A bath suits families with small children. A shower saves space and water, and it is safer for older people because there is no high edge to step over. A common compromise is a bath with a glass screen, which lets you shower comfortably without a curtain.

Where everything goes depends mainly on the soil stack. The WC needs a large waste pipe with a proper fall, so in a block of flats it usually stays close to where it was. The basin and shower are easier to move, but every extra metre of pipe has to run somewhere: in the floor or in a stud wall.

Planning a washing machine in the bathroom? Then allow for an extra water supply, a waste with a trap and a dedicated socket placed outside the protective zones around the bath and shower, as your local wiring regulations require. Put the machine where its door can open fully and it will not get in your way. In practice, the machine is often forgotten at the design stage, and the new connection then ends up running over the finished tiles.

Wall-hung WC and stud wall

A wall-hung WC on a concealed frame is easier to clean, and the cistern disappears into the wall. A stud wall built around the frame from plasterboard or aerated concrete blocks also hides the pipework and gives you a handy shelf. The frame is set to the height of the finished floor, not the bare concrete. Before tiling, test the flush and the waste for leaks.

A shower without a tray, flush with the floor tiles, looks modern and you can walk in without a step. It has one condition, though: it needs height. Under the tiles there has to be room for the trap of the drain or channel and for the fall that carries water to the outlet. In a block of flats the floor build-up is thin and you must not chase into the concrete floor slab. Height is therefore gained by raising the floor of the whole bathroom or by using low-profile floor drains.

Before you buy a channel or drain, measure how many centimetres there are from the floor slab to the planned finished floor, and check that the waste can reach the stack with enough fall. If the height is not there, a flat, low-profile shower tray is the more sensible choice. It looks similar and does not touch the building structure.

Why does the type of drain matter? With large tiles, a linear channel along the wall with a fall in one direction works better. A point drain in the middle of the shower needs a fall from four sides, so large tiles would have to be cut diagonally, otherwise their corners lift.

Many people think the tiles keep the water out. In fact neither tiles nor grout are waterproof. The water is stopped by the liquid waterproofing membrane underneath. On the floor it covers the whole bathroom and turns up the walls to skirting height. In the shower, the walls are waterproofed at least up to the shower head, and around a bath usually a few tens of centimetres above the rim.

• Corners and joints: sealing tape goes into the wall corners and along the wall-to-floor junction. It copes with small movements in the structure without cracking.
• Penetrations: sealing collars are fitted around water and waste outlets.
• Bath edge: a special bath sealing tape is bonded between the bath and the wall. If the silicone cracks later, water still cannot get behind the tiles.
• Drain and channel: the membrane is bonded to the outlet's sealing collar. Simply running it up to the edge is not enough.

The membrane goes on in two coats, the second at right angles to the first, so there are no thin spots. Before tiling, it must dry for as long as the manufacturer's data sheet says. In a block of flats, good waterproofing also protects the neighbour below you. A leak into the flat underneath is one of the most expensive mistakes a renovation can produce.

A new bathroom is more airtight than the old one. Without extraction, the steam from a shower condenses on the walls and in the joints. An extractor fan with a backdraught shutter and an overrun timer or humidity sensor helps, because it keeps running after you switch off the light. A fan can only remove air if fresh air can come in, though. Leave a gap under the door or fit a vent grille in it.

Mould in a bathroom corner is rarely the tiler's fault. Usually the cause is poor ventilation or a cold external wall. If your bathroom has an external wall, look at it before tiling. Where needed, insulate it or at least make sure that wall gets some heat.

A bathroom floor needs slip-resistant tiles, and in a shower without a tray this matters twice as much. Glossy tiles are slippery when wet and do not belong in a shower. Large tiles make a small room look bigger and have fewer joints. They do need very flat walls and floors, though, and take more effort to lay.

Before tiling starts, ask for a tile layout plan. It shows where the cuts will fall, so they are even on both sides rather than thin slivers by the door or the bath. It also shows how the tiling lines up with the door, the mirror and the taps. The tap outlets then sit in the centre of a tile or in a joint, not just anywhere.

In the shower, epoxy grout is often used instead of ordinary cement-based grout. It does not soak up water, soap does not stain it and it resists mould better. It is harder to work with and costs more, however. Corners and joints with the bath or tray are never filled with grout but with flexible sanitary silicone.

The usual heater in a bathroom is a ladder-style towel radiator, which also dries your towels. In a block of flats with central heating it is connected to the building's system, so agree any replacement or move with the building management first. After fitting, the system has to be bled and balanced. If you want the radiator to work outside the heating season too, an electric heating element can be added. It needs its own socket outside the protective zones.

Electric underfloor heating is used in bathrooms mainly to take the chill off the floor. The heating mat is laid in the tile adhesive and controlled by a thermostat with a floor sensor. Test the mat before it is covered, because once the tiles are down it cannot be repaired without breaking them out. Electrical work in a bathroom must be done by a qualified electrician, who should give you a test certificate at the end.

A few square metres see demolition workers, a bricklayer, a plumber, an electrician and a tiler, one after another. If you book each trade separately, you are the one keeping track of the order of work. Every wait for the next tradesperson pushes back the whole finish date. A company that delivers the complete bathroom takes over that coordination and the responsibility for how each trade's work fits with the next.

Choose and order the sanitaryware, taps and concealed valve bodies before work begins. The plumber needs exact dimensions and data sheets to place the outlets correctly. In practice, outlets are often set by guesswork, and when the tap arrives the spacing or the depth of the concealed body does not fit. Some taps, baths and shower screens also take several weeks to arrive.

It pays to photograph all water, waste and electrical runs before they are covered, and to keep the photos with measurements from the floor and the corners. When you later put up a shelf, you will know exactly where not to drill.

Darkened or peeling silicone is not just unsightly. Water gets through the loose joint and runs behind the tiles and under the bath. You can replace it yourself; all it takes is patience and time for it to cure.

1. Cut through the old silicone with a sharp knife or scraper along both the tiles and the bath, and pull it out along its full length.
2. Remove the residue with silicone remover, then clean the surface and degrease it with spirit.
3. If there is mould in the joint, treat it with a mould remover and let it dry completely, ideally until the next day.
4. Fill the bath with water so it settles under the weight and the new silicone does not tear when the bath is in use.
5. Apply masking tape along the joint on both the tiles and the bath to get a straight edge.
6. Apply sanitary silicone with an anti-mould additive in one smooth, continuous run.
7. Smooth the silicone with a damp smoothing tool or a finger dipped in soapy water, and peel off the tape straight away.
8. Drain the bath only once the silicone has cured, and do not use the shower for the time given on the packaging, usually around 24 hours.

Do not rush the handover. Go through the bathroom point by point:

• You have a pressure test record for the water pipework and a test certificate for the electrical installation
• Water from the shower runs to the drain or channel and does not pool anywhere, which you can check by pouring out a bucket of water
• Tapping the wall and floor tiles gives no hollow sound, which would reveal a poorly bonded tile
• Joints are even in width and fully filled, and cuts are clean and symmetrical
• All corners and joints with the bath and tray are sealed with silicone, not grout
• Taps, flush and traps do not leak even after the water has run for several minutes
• The fan extracts air and the door has a gap or grille for air to come in
• You have photos of the pipework before it was covered and the warranty documents for the sanitaryware

If something is not right, note it in the handover report together with a date for the repair. A hollow tile or a leaking silicone joint is easy to fix right after completion. Years later, the same fault can mean repairing a water-damaged ceiling in the flat below.