Adding a WC or bathroom within an existing home usually needs no planning permission, but the new drainage, ventilation, electrical work and any structural changes must satisfy building regulations. Replacing existing fittings is different from creating a new bathroom in a previously dry room. [1] [2]
Check that the layout can work
Confirm the position of the WC, basin, bath or shower together with the doors, ventilation and drainage route. A small room is not suitable merely because the fittings fit on a plan. The design needs to provide the sanitary and washing facilities required for its use. [3]
A toilet needs associated handwashing facilities. Approved Document G allows these in the same room or in a suitable immediately adjacent space forming the sole access to it. In a dwelling, a room containing both the WC and handbasin does not need an additional separation lobby before a kitchen: a separating door is the relevant arrangement. [3]
If an existing ground-floor toilet provides required accessible facilities, refurbishment should not remove that provision or make it less accessible. Consider the effect of a new door swing or reduced circulation space before finalising the layout. [4]
Establish the drainage route before ordering fittings
Waste from toilets, basins, baths and showers belongs in the foul drainage system, not a rainwater-only drain. Ask for the proposed connection and pipe route to be checked as part of the design, including any work needed to the existing drainage. [5]
A pumped or macerating arrangement is not a universal way around an unsuitable layout. Approved Document G's guidance on small-bore pumped systems includes the availability of a suitable gravity-drained sanitary convenience elsewhere in the dwelling. Establish that the proposed system and the home's facilities satisfy the relevant guidance before relying on it. [3]
Provide the right ventilation
A new bathroom or shower room needs appropriate extraction. For a room containing only a WC, an appropriately sized openable window may provide an alternative in the circumstances described by the guidance; an enclosed shower room is not the same situation. [6]
The ventilation arrangements should be planned with any new partitions. A new room must not remove the ventilation route serving another space. Show the fan and duct route where extraction is needed, rather than leaving only an electrical point for a fan with nowhere suitable to discharge. [6]
Coordinate electrical and structural work
Bathrooms have particular electrical safety requirements. Under Approved Document P, a new circuit, replacement consumer unit and additions or alterations to an existing circuit within the defined bath or shower special location are notifiable work. The electrician should confirm the appropriate compliance and notification route. [7]
Where the layout needs structural alterations, obtain a suitable design. New openings or changes to supporting walls are separate from fitting sanitaryware and can require building control involvement even if the plumbing installation is straightforward. [8]
What changes for work in 2027?
The 2026 Approved Document F includes guidance for work to existing dwellings. It takes effect for non-higher-risk building work on 24 March 2027, subject to transitional arrangements. Check the edition applying to the actual work, particularly when a new wet room forms part of a wider airtightness or window-upgrade project. [9]