Refitting or adding bathrooms


As with re-fitting kitchens, there’s normally no need for planning permission unless the building is listed. Building Regulations are only likely to apply where you decide to add a new bathroom, for example in a former bedroom or storage area. This may include some or all of the following:

  • New drainage
  • New ventilation
  • Structural alterations, e.g. taking out walls and chimney breasts
  • Gas fitting and new boiler/hot water cylinder installation
  • Electrical work

The last two items can usually be self-certified by approved installers, but Building Control will need to carry out inspections for new work such as drainage and structural alterations. Ventilation should also be provided with ducted extractor fans and trickle vents to windows.

Refitting a bathroom

When it comes to replacing an existing bathroom suite, the job is made considerably easier if you select new fittings that match the old ones in size as closely as possible, especially baths and shower trays. With a bit of luck they should simply ‘slot in’ with minimum upheaval – although connecting up a new suite to decrepit old imperial-sized pipes can require a certain amount of ingenuity.

Beyond the choice of sanitary fittings and taps, there are other design issues to ponder, such as whether to re-tile the walls, fit new towel rails, and install storage cupboards. While you’re at it, it’s worth upgrading the bathroom to comply with current Building Regulations in terms of ventilation – fitting a ducted extractor fan will help reduce condensation and mould. Also lining the main walls with insulation, upgrading the lighting and fitting secondary or double glazing can be worthwhile energy efficiency improvements.

Also, pay careful attention to the detailing at the edges of baths and shower trays as the joints where fittings abut the walls are a common cause of leaks. Use purpose-made sealing trim strips or a suitable silicone mastic sealant.

Adding a new bathroom

Where you want to install a totally new bathroom, the existing hot and cold water supplies will need extending. The waste pipes will also need to be carefully planned so they connect into the existing system, plus you may need some new central heating pipework for any additional radiators or towel rails. Don’t forget to allow for the boxing-in of surface-run pipework so that it’s neatly concealed. The only restriction on DIY plumbing is competency, so this is an area you may want to tackle yourself. The electrics may also need extending, although sockets are not permitted in bathrooms.

If space permits, it’s normally a good idea to have a separate shower cubicle within a bathroom, rather than just a mixer over the bath. Or you may like the idea of a walk-in wet room, with fully tiled waterproof floors and walls.


Most pipework is run in copper, although plastic pipes are increasingly used for new work.

When it comes to running pipes in timber floors the critical points structurally in joists are the centre and the ends. In traditional joists, notches should be cut from the top (no deeper than 1/8th depth) and it’s a good idea to fit small steel shields over the top of cut notches to protect pipes from subsequent puncturing should anyone carelessly hammer nails into floorboards.

But modern ‘I-joists’ must not be cut – they have pre-formed slots to accommodate pipes and cables. The Building Regulations require new water supply pipes to be fitted with non-return valves to prevent ‘back siphonage’, and these can also provide a handy on/off control to allow maintenance works. To prevent any risk of scalding, temperature controlled thermostats should be fitted to hot water supplies to showers and baths.

Waste pipes

Waste pipes need to be laid to suitable falls with sufficient support-clips so they don’t sag. Internal white plastic waste pipes and fittings are push-fit and should be surface run rather than buried in floors. When designing a new bathroom you need to take account of the fact that there is a maximum distance that you can locate your new basin, WC and bath from the soil and vent pipe waste stack (SVP) before there is a risk of ‘siphonage’ occurring. This constraint can influence the layout of new bathrooms. However it may be possible to fit special ‘anti-siphonage’ traps or bigger bore pipes.

Installing a new bathroom or WC ‘Durgo Valves’ (air admittance valves) usually need to be installed. Unlike conventional SVPs these vent automatically and relieve excess pressure without emitting odours. They don’t need to terminate way up at roof level, and instead can be neatly boxed in, and are sometimes placed unobtrusively in loft spaces.

Foul and surface water

There are two types of waste water: rainwater from gutters and foul waste from bathrooms, cloakrooms, kitchens and utility rooms. These must not be mixed up, as it can lead to problems with flooding and pollution, even causing disease. Waste plumbing for new bathrooms must be connected to the underground foul drains, not into a handy nearby rainwater downpipe for example. This is something that Building Control will want to check before issuing a completion certificate.


One of the first questions you need to ask when designing a new bathroom is ‘where are the drain runs?’ This tells you where it would be realistic to fit new bathrooms without running into plumbing problems. Where a new WC is installed some distance from the foul drains, one possible solution is to install a macerator. These work by mashing up the waste so it can be pumped out through conventional narrow-bore 38mm pipes rather than requiring the normal larger 100mm WC pipes. But because they rely on electrical power, the home must have at least one conventional WC, in case of power cuts.


Most modern baths are either lightweight steel or acrylic, but they still need to support a substantial weight of water and occupant(s) when in use. So it’s important that the feet are firmly supported. Some traditional cast iron baths are extremely heavy with miniscule feet which transfer incredibly high loadings to the floor surface. So it may be necessary to first strengthen the floor.


To operate effectively, showers often require the water pressure to be beefed up with a powerful pump together with a separate new cold supply. Shower trays can also be prone to developing leaks, the worst offenders being thin acrylic ones which can be prone to distortion. Ceramic or stonecast trays are generally preferable. Or you could opt for a simple mixer over the bath with a shower screen (although these can be difficult to make fully watertight).