Bathroom and toilet core renovation: cost of a bathroom and toilet core in a panel block flat 2026

In a large panel apartment block, the bathroom and toilet core is the group of rooms that need water and drainage. It is usually the bathroom and a separate WC, built around the vertical stacks. In older blocks the core was a ready-made laminate pod. It was lifted into the flat as a finished unit. The walls are thin laminate boards on a timber or metal frame, with the pipes running loose behind them. In later building systems the cores were made from thin panels or blocks, or built in masonry. Each system has slightly different dimensions, a different stack position and a different way of fixing the walls. So two flats with the same floor area can behave very differently once work starts.

The core includes its walls, its floor, the pipework from the stack to the fittings, and the ventilation into the shaft. It does not include the floor slab above, the external or load-bearing walls, or the stacks themselves, which serve the whole block. The kitchen often backs onto a core wall and takes its water and waste from the same service duct. The ventilation shaft is usually shared by every floor above and below. If you understand this split before you start, it is much easier to agree the work with tradespeople and with the building management.

The water risers, the soil stack and sometimes the gas supply are shared parts of the building. Decisions about replacing them or shutting them off sit with the building management or owners association, not with the individual flat owner. In practice, a plumber cannot simply turn off the water in the riser. The date is announced, neighbours are warned with a notice in the entrance, and the valve is often opened and closed by someone the management appoints.

In practice it often happens that the building plans to replace the stacks, block by block, within a year or two. In that case it pays to find out the schedule. You can then time the core so that a new stack does not have to be connected through finished tiling later on. If no replacement is planned and the stack in your flat is in poor condition, you may be able to agree with the management to replace the section inside your flat. Get the agreement in writing. It should say who is responsible for the connection to the rest of the stack and who pays for any damage to neighbouring flats.

Whether your work needs approval or notification depends on its scope, so nobody can promise a blanket answer. If the work affects load-bearing structure, shared services or the layout of the flat, it is sensible to check the procedure directly with your local building authority. Permission from the building management or owners association is a separate matter. Approval from the local building authority does not replace it. If you own a leasehold flat, it is also worth checking what your lease says about alterations.

When the core is opened up, materials that are no longer used sometimes come to light. In some blocks, ventilation ducts or parts of the waste pipes are made of asbestos cement. They look like grey concrete with a fibrous texture. As long as they are whole and undamaged, they are not dangerous. The problem starts with cutting, breaking and sanding, which release fibres.

Asbestos cement should only be removed by a licensed asbestos contractor who follows the rules for that specific job. Neither a homeowner nor an ordinary demolition crew should touch it. If asbestos is suspected, stop the strip-out in that area and have the material assessed. Because these ducts are often part of the shared ventilation, the decision also goes through the building management. Apart from asbestos, you may find old bitumen adhesives under the floor tiles, lead seals or rusty steel sleeves. None of this is a disaster. It just needs to be included in the plan for strip-out and waste removal.

Instead of laminate, most cores today are closed in with aerated concrete blocks. They are strong and simple to work with. You can fix a cabinet, a mirror or even a heavier water heater without much thought, as long as you use fixings made for aerated concrete. The wall copes better with moisture and will not fall apart if there is a leak. The downsides are weight, wet trades and drying time for the plaster.

Plasterboard is lighter and quicker, and the cavity between the boards lets you run services without chasing the wall. In wet areas, though, you need moisture-resistant or cement boards and a denser stud frame, usually as the system manufacturer recommends. Heavy items need noggins or pattresses fitted in advance, otherwise fixing them gets complicated. For sound, what matters is filling the cavity with mineral wool and isolating the frame from the ceiling and floor. You hear a toilet flush far more clearly through a poorly designed plasterboard wall than through masonry.

A common compromise is to build the outer walls of the bathroom and WC in blockwork and run the services in a plasterboard boxing or service wall. The walls are solid, and the services stay accessible through access panels.

The core partitions are usually not load-bearing, so the layout can change. Combining the bathroom and WC frees up space, but you lose a second room for the morning rush. For families with children, it is often better to keep a separate WC and move the door instead, so that a washing machine fits in the bathroom. Doors are often moved for another reason too: the original ones opened into the hallway and blocked the way into a bedroom.

The limit is the waste. Drainage needs a fall towards the stack, and in a panel block you cannot sink pipes any deeper into the floor. The further the toilet or shower is from the stack, the higher the connection has to be, and the sooner you end up with a step or a raised plinth. Never cut, chase or drill through the floor slab without a structural engineer's assessment. The same applies to load-bearing walls next to the core. A washing machine needs its own supply, a trapped waste and a socket, ideally placed so the machine can be pulled out for servicing. Bathroom details such as waterproofing, level-access showers, tiling or toilet seat height are covered in separate guides.

Water and waste

Older cores have galvanised steel pipes that fur up inside and corrode at the joints. You may also find aluminium or copper sections from later repairs. When the core is renovated, the old pipes are usually replaced completely, right up to the isolating valve at the stack. New pipework normally runs inside a service wall, which also hides a concealed cistern frame and gives a flat surface for tiling. Isolating valves, water meters and drain rodding points must stay accessible. Nobody enjoys reading a meter through a narrow gap behind a mirror.

Electrics

Many older panel blocks have aluminium wiring. It becomes brittle, connections work loose, and under today's loads from washing machines, tumble dryers and heaters it can overheat. When the core is renovated, new circuits are run in copper. The connection to the rest of the flat is made with terminals designed for joining aluminium to copper, ideally at the consumer unit. Bathrooms have defined zones that limit where sockets and lights can go, and these are covered in separate bathroom guides. Electrical work should only be carried out by a qualified electrician, and you should ask for the electrical certificate when the job is finished. Without it, an insurance claim or the sale of the flat becomes much harder.

The bathroom and WC in a panel block have no window and are ventilated into a shared shaft. In some blocks the ventilation is natural. In others, a central fan on the roof keeps the shaft under negative pressure. A powerful fan of your own does not belong in a system like that without careful thought. It can push air into neighbouring flats or upset the airflow in the whole riser.

If a motorised fan is fitted in the core, it should have a backdraught shutter so that smells and steam from neighbours do not come back into your flat. In blocks with central extraction, the building management usually has to agree, and sometimes only a grille or an adjustable vent is allowed. The opening into the shaft must not be reduced or blocked up. In practice it often happens that the original ventilation duct gets damaged during the strip-out. Repairing a shared duct then has to go through the management, so the area around the shaft is best broken out carefully and by hand.

In a panel block, the kitchen units often stand against the core wall and connect to the same stack. While the core is stripped out, it is the best moment to prepare new water and waste points for the kitchen, including a supply for a dishwasher. Otherwise you would have to open up the finished bathroom wall later. If you plan to replace the kitchen in a year or so, it is worth running the valves and waste out now and capping them off.

With a plasterboard service wall, remember that kitchen wall units will hang on the other side. Fit noggins or pattresses in advance, or build that wall in blockwork. Moving the sink along the worktop runs into the same fall limits as in the bathroom. A long horizontal waste under the units tends to block and can be noisy.

Renovating the core means the flat will have no bathroom and no toilet for a while. If you stay in the flat, you will need an arrangement with family, neighbours or a short-term rental. Some firms install a temporary toilet for a few days, but that does not solve showering. The hardest days are usually the first days of strip-out and the days when one trade follows another with no water available.

Stripping out a core is noisy and dusty. The house rules usually set the hours when noisy work is allowed, and they are often stricter at weekends. It is polite to let neighbours know in advance with a notice in the entrance. Protect the lift and stairs from damage and clean them regularly. Dust gets through closed doors, so it is sensible to cover furniture in every room, not just near the core.

The timeline can only be squeezed so far. Plaster and skim coats need to dry, and made-to-order sanitaryware can arrive late. A realistic plan builds in some slack. Order sanitaryware as soon as you have made your final choice, not when the tiling starts.

Strip-out and services are a job for professionals. Preparing the flat, however, is something you can do yourself, saving the firm time and yourself some stress.

1. Clear the bathroom, WC, hallway and any kitchen cupboards against the core wall so there is free access to the stack.
2. Photograph the existing core, isolating valves, water meters, valves and consumer unit, including the circuit labels.
3. Note the readings on the water meters and any heat cost allocators, and send a dated photo to the building management.
4. Mark the main water valves in the flat and the circuit breaker that supplies the core with coloured tape.
5. Cover the hallway and bedroom floors with protective sheeting and tape, and seal around bedroom doors so dust cannot get through the gaps.
6. Put up a notice in the entrance with the strip-out dates and a contact for the person in charge.
7. Arrange alternative washing and toilet facilities for the whole job, and agree a place for the skip in advance, following the instructions of the building management or the council.

• isolating valves, water meters and rodding points are accessible through access panels,
• you have received a record of the pressure test for the pipework,
• you have received the electrical certificate for the wiring,
• there are photos of the services before they were covered, with the routes marked,
• the connection to the stack is dry and the stack is undamaged,
• the ventilation grille or fan draws air and the backdraught shutter works,
• doors open freely and do not hit the sanitaryware or the washing machine,
• the kitchen water and waste points are in place and capped as agreed,
• the partitions are solid and there is reinforcement where cabinets will hang,
• the area around the ventilation shaft and the shared parts of the building are undamaged,
• the building management has been told the work is finished and has received the meter readings.