Why bath and shower rooms are split into zones, the IP rating each needs, and when work there becomes notifiable.
Why bathrooms are split into zones
A bath or shower fills a small room with water, wet skin and earthed metal pipework and taps all at once, which is exactly the combination that turns a small electrical fault into a fatal shock. BS 7671 responds by splitting the space around a bath or shower into zones, each with its own rules for what can be installed and how well it must be protected against water.
Zone 0, 1 and 2
Zone 0 is the inside of the bath or shower tray itself: anywhere water can sit. Any electrical equipment here needs an IPX7 rating, which covers temporary immersion, and in practice almost nothing mains-powered is fitted this close.
Zone 1 is the space above the bath or shower, up to the height of a fixed shower head or 2.25 m above the floor, whichever is higher. A shower without a basin, fitted to a wall rather than over a bath, instead gives Zone 1 a 1.2 m radius around the fixed shower outlet. Equipment here needs at least IPX4, which covers splashing from any direction, and more if water jets are likely.
Zone 2 runs a further 0.6 m out beyond Zone 1, to the same height; a shower without a basin has no Zone 2. It also needs at least IPX4. Only equipment built for the location, such as a shaver socket to the relevant British Standard, belongs this close to a bath or shower; general-purpose sockets do not.
A boiler or other appliance fitted in a bathroom cupboard is not exempt from any of this: if the cupboard sits inside these zones, the equipment inside it still needs the right IP rating, and it still needs to be reachable for safe isolation and servicing.
RCD protection and notification
Every low-voltage circuit serving a room containing a bath or shower needs additional protection by a 30 mA RCD. This is on top of, not instead of, the IP ratings above.
Because this area carries extra rules, altering or adding to a circuit inside it can make the work notifiable under Part P, even when the same alteration elsewhere in the house would not be. Confirm the current notification route before starting.