Bathroom Zones 18th Edition

This article will comprehensively take you through the required installation practices for bathrooms containing bathtubs, showers and wet rooms respectively. Given the elevated risk involved, electricians must undertake a range of safety precautions to protect domestic and commercial users. Candidates are advised to focus on the specifications attached to each ‘zone’, and understand corresponding measurements which are essential to safe installs.

Zones & Environments

Our guide will walk you through each context (i.e., bath, shower, wet room) and the zonal considerations for these environments. Again, candidates and electricians must flag if any information is ambiguous as specialist locations can be volatile. Installations must be carried out with confidence and assurance.

As mentioned, a bathroom can have three main function variations: bathtubs, shower wells, or a wet room facility. There are three associated zones for bath tubs and shower wells, but only two accredited to wet rooms (reasons discussed later in text). Each zone has multiple component parts to consider, due to likelihood of wetness exposure. In a very broad sense, the zones become less risky in ascending order i.e., Zone 0 is high risk, ‘Outside Zone’ relatively low risk.

Best Practice

Before starting, electricians should refer to Section 7 of the bs7671 18th edition. This part details appropriate regulations and advisory notes on specialist locations such as bathrooms. Remember, the guide breaks down how to approach a task from start to completion, so it is well worth reviewing prior to installation.

The ‘box’

An element which is consistent throughout said implementation is the ‘box’. This refers to an imagined parameter that follows a standard measurement guideline regardless of context, the height of which should always be 2.25m (or the highest fixed head or outlet, whichever is higher). The width is dependent on bathtub, shower basin or wet room fixed water outlet position. For reference, most modern bathrooms measure roughly between 2.5-3m, so there should be ample room between the upper box level and ceiling.

Furthermore, any 230V transformers deployed must be 30mA (milliamperes) protected, and guidelines must be followed on whether these units can be facilitated inside or outside bathroom spaces (depending on room size).

The below information advises on each fitting situation, highlighting regulations and nuances depending on room size, layout and water vessel. It is important to remember that all rooms differ slightly, and therefore candidates should account for appropriate adaptation of the below guidelines in relation to their workspaces.

Opening Questions

The most pertinent questions always serve to provide an understanding of three key areas. Firstly, what the ‘zones’ are, secondly how they are calibrated, and, thirdly, what wiring needs to be RCD protected. This guide should ultimately answer all those questions for you, but, as referenced above, it’s important to ascertain this information in the context of the installation, given the potential for variance.


For bathtubs, our ‘box’ size should correspond to the following criteria:

Height: As standard, electricians should mark this at 2.25m (or the highest fixed head outlet, whichever is higher).

Width: This should be the width of the bathtub, plus 0.6m (60cm). Therefore, if the bathtub measured 0.7m (70cm), your box width would be 1.3m (130 cm)

The surrounding perimeter of these dimensions pertains to your box area. As mentioned, bathtubs have three fixed zones.

Zone O

This area is the most dangerous region of installation, and, unsurprisingly, therefore, extra precautions must be taken. Zone 0 relates to the physical space within the tub, or, simply put, the area in which one would sit in if taking a bath.

When installing in this zone, electrical equipment should be IPX7 rated, which dually accommodates submersion. It is critical that voltage does not exceed 12VAC or 30VDC in this area. Furthermore, it must be a SELV (separated extra-low voltage) circuit only, and a 230V transformer supporting this end must be located outside of the bathroom (zones). ELV (extra low voltage) cables are permitted to travel in this zone and others.

Zone 1

This space refers to the standing area above the bathtub, from the floor, up to the upper limit of the box. In terms of width, this zone includes the full expanse of the bath, not just the seating area. Therefore, candidates should consider external bathtub handles when calculating this space.

If the area underneath the tub is easily accessible, then this should be integrated into Zone 1. However, if it is blocked by a barrier or panel (requiring a key/tool to gain entry), this is classified as the ‘outside zone’. This should be prepared accordingly to the provisions set out under this space (information on this area later).

Any lighting installed should be either coordinated on SELV or PELV (protective extra-low voltage) circuits, and limited to 25VAC or 60VDC. If an electric shower is required, then this must comply with an IPX4 rating.

Zone 2

Zone 2 is the area immediately adjacent to the bathtub, i.e., the additional 0.6m added for safety purposes. Again, any equipment should be subjected to an IPX4 grading.

However, in relation to shaver sockets, electricians should integrate sockets at BSEN 61558-2 standard. They should also look to position where potential water spray is unlikely. Self-switches and sockets are permitted in this area.

The ceiling pull switch for any associated shower facility should be mounted above the 2.25m threshold. Only the operating chord is allowed to be present in Zone 2.

The ‘Outside Zone’

Clearly, this space refers to the rest of the room, inclusive of the area above the ‘box’. This should be broken down into two fixed parts:

Part 1: This pertains to the space from where Zone 2 ends, up to a point three metres away from the outside edge of the bathtub. If this run is intercepted by a wall (which, in most domestic cases it will) then the zone accordingly ends when it meets this barrier.

Towel rails or heaters (supplied by 230V) can be installed in this space, but must be permanently wired into a flex outlet or comparable function. The outlet can be switched on either outside or inside, dependent on client preference, but all circuits must 30mA, RCD protected.

Sockets at 230V are not permitted, however if present in spaces beyond three metres above the bathtub, they become agreeable. Again, these sockets must be 30mA, RCD protected.

Part 2 alludes to the space more than three metres past the bathtub, immediate area above the box and the surrounding expanse at this height.

Candidates should envisage an imaginary line from the top right-hand corner of the box, all the way through to the opposite wall. Any space above this is included in Part 2. Ceiling lights will fall into this bracket, and there is no requirement therefore for these to be IP rated. All of these parts fall outside the measured ‘box’.


Associated shower proceedings essentially follow the same guidelines as bathtub installs, however it’s important to note that there are nuances due to the shape of the unit.

For showers, Zone 0 alludes to the foot basin space. Zone 1 is the immediate area above this up to 2.25m in length, and mimics the measurements of the foot basin in width. And Zone 2 is again 0.6m, but this time registered from the outside edge of the foot basin. Outside Zones follow the same guideline patterns as a bathtub context.

Wet Rooms

Wet rooms vary substantially to the environments discussed earlier.

Given that a ‘wet room’ is ultimately a free-standing space with no attached unit, Zone 0 is given a projected line, rather than being attached to any physical entity. This measurement is 100mm (10cm) up from ground level. Zone 1 is the length up to the 2.25m upper level.

Each shares the same width, which is defined as a circle 1.2m in radius, with its centre point relating to its fixed water outlet or plughole. These dimensions construct the overall safety ‘box’. In examples where partitions disturb the circle’s flow, it will wrap itself around, still aligned to the aforementioned measurements.

There is no Zone 2 in a wet room capacity. Therefore candidates should assume any space external to Zones 0 & 1, is the ‘Outside Zone’.

Underfloor Heating

Where underfloor heating is installed, electricians must ensure that any cables that pass-through Zones 1 & 2 are 30mA, RCD protected.

In Summary

To summarise, it’s perhaps best to highlight the commonalities between all instalment environments:

  • All 230V Transformers must harbour 30mA RCD protection.
  • Any cables that pass-through bathrooms, but are not used in this space, must also be 30mA RCD protected.
  • The upper box threshold should always be 2.25m (or the highest fixed head or outlet, whichever is higher). This applies to all ‘bathroom’ contexts, whether navigating bathtub, shower, or wet room functions.
  • Where SELV or PELV circuits are in operation, then the 230V transformer supply agent must be outside the bathroom. Only extra low voltage cables are permitted.

Consult the guide, ask for help if unclear

Candidates who are unclear on IPX grading, BSEN 61588-2 sockets, transformers, RCD protection, or voltage considerations, should consult their bs7671 18th edition guide. This will provide a full and thorough analysis on the definition of this terminology, and also their suitable application.

Given the potential hazards involved, electricians should treat the aforementioned spaces with increased caution. The regulations set-out detailed guidance on how to safely install electrics in bathroom spaces. Therefore, make sure you always refer to your bs7671 guide when preparing works.

Guidance for locations containing a bath, shower or wet room is located in Part 7 (Special Installations & Locations), Section 701, and includes a full set of instructions along with supplementary diagrams. As per its installation support process, candidates will be walked through each stage of the task. Judging workspace conditions, considering the provision of equipment, subsequently selecting the right equipment, and the commissioning through appropriate testing and inspection. Therefore, any information you require should be present in this all-encompassing workbook.

If any of this information is unclear, then please consult your course convenor, or appropriate electrical professional in the trade.