What Are the Key Regulations and Planning Considerations for a Bathroom Refit?

Summary

Most bathroom refits in the UK are straightforward from a regulatory standpoint. Replacing a bath with another bath, changing tiles, or upgrading sanitaryware in an existing bathroom room does not require approval if the drainage and ventilation are unchanged. Where the work tips into notifiable territory — new en-suite, relocated drainage, new electrical circuit, or structural alterations — the regulatory picture becomes more complex and Building Regulations approval becomes mandatory.

The regulations that apply to bathroom work span multiple Approved Documents: Part P (electrical safety), Part G (water efficiency), Part F (ventilation), Part H (drainage), and potentially Part B (fire safety, for loft conversions with new bathrooms) and Part M (accessibility). Understanding which Parts apply to a specific project avoids both the cost of non-compliant work and the risk of not getting sign-off when the property is sold.

This article covers the main regulatory considerations and the practical space planning requirements for both standard refits and new bathroom installations.

Key Facts

• Part P (Electrical Safety) — notifiable work includes installing a new circuit to a bathroom, or adding a socket (which is not permitted in a bathroom in any case within Zone 1 or 2); like-for-like replacement of a shaver socket or fan is not notifiable; a Part P-registered electrician can self-certify; non-registered contractors must notify building control
• Part F (Ventilation) — new bathrooms must have mechanical ventilation if they have no openable external window; minimum extract rates: 15 L/s intermittent (fan that runs while in use and for a run-on period) or 8 L/s continuous (whole house ventilation system); BS EN 13141 covers fan performance
• Part G (Water Efficiency) — applies to new dwellings and material changes of use; maximum 125 L/person/day whole dwelling water consumption; basin taps maximum 6 L/min, shower maximum 8 L/min, WC maximum 4 L/flush (or dual-flush 2.6/4 L); does not apply to a standard refit of an existing bathroom
• Part H (Drainage) — all waste connections must maintain trap seal depth (min 75mm for WC, min 38mm for basin and bath); all connections to soil stack must be via an approved boss or proprietary connector; no unsupported pipe runs longer than BS EN 12056 allows [verify]
• Zone 1 — directly above the bath or shower tray, up to 2.25m above the floor; only IPX7 (fully waterproof) fittings permitted; no switches
• Zone 2 — 0.6m horizontally from the edge of Zone 1; IPX4 (splash proof) fittings minimum; shaver sockets with transformer to BS EN 61558-2-5 are permitted
• Outside zones — normal electrical fittings permitted but switches outside Zones 1 and 2 should be cord pull or outside the room
• BS 6465-1:2006 — Sanitary installations; code of practice for the design of sanitary facilities; sets minimum space standards around fittings
• HMO standards — Houses in Multiple Occupation have additional requirements for bathroom provision; local authority licensing conditions typically specify minimum bathroom-to-person ratios
• Planning permission — not normally required for a bathroom refit; required if the building is listed (any internal alteration needs Listed Building Consent) or if the work affects the building's external appearance

Quick Reference Table

Detailed Guidance

Electrical Zones and IPX Ratings

The bathroom electrical zone system under BS 7671 (IET Wiring Regulations, 18th Edition) divides the bathroom into three areas based on proximity to water:

Zone 1 — the volume directly above the bath or shower tray, within the basin of the bath/tray footprint and up to 2.25m above the floor. The specific minimum IP rating for Zone 1 is IPX5 where a water jet is used (e.g. shower) or IPX4 for a bath where no water jet is expected. In practice, IPX7 or IPX5 rated fittings are used in Zone 1. No switches, socket outlets, or luminaires that are not rated for zone 1 are permitted. Shower pumps, fans with approved connections, and shower units are the only devices that may be installed here.

Zone 2 — 0.6m horizontally outside Zone 1 (and also the ceiling above Zone 1 at greater than 2.25m or 3m depending on configuration). Minimum IPX4. Shaver supply units to BS EN 61558-2-5 are permitted here. Pull-cord switches can be sited at the perimeter of Zone 2 or outside it.

Outside zones — all areas of the bathroom outside Zone 2. Normal electrical accessories are permitted here, but in practice most bathrooms are small enough that there is no usable wall space outside the zones. Light switches should be outside the bathroom entirely (if possible) or be a pull cord within the bathroom. Socket outlets must not be installed within the bathroom except for shaver sockets in Zone 2.

Ceiling lights — the ceiling is technically Zone 2 if within 0.6m of the edge of the bath/shower, outside Zone 2 beyond that. Most bathroom ceiling lights should be rated IP44 minimum for general protection; IP65 or better is good practice in shower rooms.

Part F Ventilation Requirements

Building Regulations Part F requires that bathrooms without openable external windows (internal bathrooms, en-suites in inner rooms) must have mechanical extract ventilation. The required extract rates are:

• 15 L/s (54 m³/hr) — for intermittent extract (fan operates during use and for a run-on period after leaving the room; typical overrun timer 15–30 minutes)
• 8 L/s (28.8 m³/hr) — for continuous operation (whole house ventilation systems, MVHR, or continuously running low-volume fan)

Bathrooms with openable external windows are not legally required to have mechanical extract, but a fan is strongly recommended to control humidity and condensation, particularly for a shower room.

Fan performance must be to BS EN 13141. Most standard bathroom fans are rated for 15–30 m³/hr free air delivery — this is usually adequate for the regulations but is based on the fan running at design conditions; actual installed performance may be lower if duct runs are long or tortuous. Duct lengths should be minimised; bends add resistance; use 100mm duct in preference to 75mm for longer runs.

For MVHR (Mechanical Ventilation with Heat Recovery) systems, the bathroom extract point forms part of the extract branch. The extract rate at the bathroom terminal unit must achieve at least 8 L/s continuous. Design by a qualified installer is required to meet Part F and achieve balanced flows throughout the system.

Part G Water Efficiency

Part G applies to new dwellings and to material changes of use (e.g. converting offices to flats). It does not apply to a standard bathroom refit in an existing home. However, when planning a new bathroom in a new extension that creates a new dwelling, Part G compliance is required.

The 125 L/person/day limit is calculated for the whole dwelling using a water calculator. Key limits per fitting:

• WC: maximum 6 L/flush (single flush) or 3/4.5 L (dual flush — not exceeding 6 L average)
• Basin tap: maximum 6 L/min
• Bath: no direct limit on bath volume, but the total dwelling calculation must work out
• Shower: maximum 8 L/min

Most modern WRAS-approved fittings comfortably meet these limits. WRAS (Water Regulations Advisory Scheme) approval is also required for all fittings and valves in contact with the supply system — a product that is not WRAS-approved is not compliant with the Water Regulations (Water Fittings Regulations 1999).

Space Standards (BS 6465-1)

BS 6465-1:2006 defines minimum space standards for sanitary fittings in domestic and commercial buildings. The key minimum clearances for domestic bathrooms are:

• WC pan — minimum 600mm frontage clear space in front of the pan
• Washbasin — minimum 600mm frontage clear space; 100mm each side to wall
• Bath — minimum 1100mm clear access along the long side for transfer from a wheelchair (accessible bathrooms); 700mm clear access for standard ambulant bathrooms
• Shower tray — minimum 700mm × 700mm internal shower tray; 900mm × 900mm recommended

For en-suites in domestic settings, these standards are guidance rather than strict legal requirements — the Building Regulations do not specify minimum bathroom sizes in private dwellings (except in social housing and for accessible bathrooms under Part M). However, they reflect good practice and should not be significantly undercut.

For HMO (House in Multiple Occupation) properties, local authority licensing conditions typically specify minimum bathroom provision (e.g. one bathroom per 5 persons) and may specify minimum dimensions. Always check the specific HMO licence conditions.

Wet Room Gradients and Drainage

A true wet room (no shower tray; shower waste set into the floor) requires a floor gradient of 1:80 or better falling toward the waste to prevent ponding. In practice, 1:60 is easier to achieve without noticeable slope. The gradient must be consistent — a bowl-shaped floor with the waste at the low point rather than a flat floor with a sudden step.

Pre-formed wet room formers (Marmox, Wedi, Schluter Kerdi-Shower) provide a pre-sloped deck with a central or offset waste position. These are far easier to achieve an acceptable gradient with than site-formed screeded floors.

Where the structural floor is timber (common in upstairs en-suites), the floor must be stiffened to prevent deflection under load, which would cause the drainage gradient to change and potentially crack the tiled surface. A secondary subfloor of 18mm WBP ply on noggins between joists, with the wet room former on top, is the standard approach.

Frequently Asked Questions

Does a bathroom refit need Building Regs if I'm using a local plumber?

A standard bathroom refit (replacing like-for-like sanitaryware, tiling, and accessories without altering the room structure, drainage layout, or electrical circuits) does not require Building Regulations approval regardless of who does the work. However, any new drainage connections, new electrical circuits, or significant ventilation changes do require either notification to building control or use of a competent person scheme registrant.

Can I put a socket outlet in a bathroom?

No standard socket outlets are permitted in UK bathrooms. The only permitted socket-type outlet is a shaver supply unit to BS EN 61558-2-5, which provides isolated 230V and 115V outputs for electric shavers through a safety transformer. This can be installed in Zone 2 (0.6m from the bath/shower edge) or outside the zones. Standard socket outlets (for hairdryers, etc.) are not permitted anywhere within the bathroom.

Do I need planning permission for an en-suite in a bedroom?

Not in most cases. An en-suite bathroom created from within an existing bedroom — without altering the external appearance of the house — is Permitted Development. Exceptions include listed buildings (Listed Building Consent always required) and properties where Permitted Development rights have been removed by a planning condition.

What ventilation is required for a bathroom with a window?

A bathroom with an openable external window of sufficient area is not legally required to have mechanical ventilation under Part F. However, Building Regulations guidance recommends mechanical extract even where a window is provided, particularly for showers. For a standard bathroom, a 15 L/s fan is strongly recommended to control moisture and prevent condensation and mould growth.

Regulations & Standards

• Building Regulations Part P (2013) — electrical safety in dwellings; notifiable work in bathrooms

• Building Regulations Part F (2021) — ventilation; minimum extract rates for bathrooms

• Building Regulations Part G (2016) — sanitation, hot water safety, and water efficiency; 125 L/person/day

• BS 7671 (IET Wiring Regulations, 18th Edition) — electrical installation requirements; bathroom zones and IP ratings

• BS 6465-1:2006 — Sanitary installations; code of practice for design of sanitary facilities

• IET Wiring Regulations (BS 7671:2018) — 18th Edition; bathroom zone definitions and IP rating requirements

• Building Regulations Approved Document F (2021) — ventilation requirements and extract rates

• Building Regulations Approved Document G (2016) — water efficiency and WRAS requirements

• WRAS — Water Regulations Advisory Scheme — product approval for water fittings

• BS 6465-1:2006 — sanitary installation design standards

• bathroom waterproofing tanking — waterproofing before tiling in wet areas

• freestanding bath installation — structural and plumbing considerations

• bathroom heating options — electric towel rails, UFH, and IP zone requirements

• wetroom construction — gradient, drainage, and waterproofing for fully wet floors