Change of use

Planning Supporting Statement for a Flat Conversion: What to Include

6 June 2025 · 6 min read

Converting a house into two or more self-contained flats is a change of use that requires planning permission in virtually all circumstances. It is a commonly made application, but one that many LPAs scrutinise carefully — particularly where local plan policies seek to protect the existing housing stock of larger family homes. A strong supporting statement is essential to making the case effectively.

Why does a flat conversion need planning permission?

The change of use from a single dwellinghouse (Use Class C3) to two or more self-contained flats constitutes a material change of use under the Town and Country Planning Act 1990. Unlike some other changes of use, this conversion is not permitted development — it always requires a planning application.

The application is made as a full planning application and must be assessed against the development plan for the area and other material considerations, including the NPPF.

The policy framework for flat conversions

At national level, the NPPF 2023 supports the delivery of a wide mix of housing types and sizes. Paragraph 62 requires local planning policies to be informed by and be consistent with the needs of different groups in the community, and paragraph 63 requires policies not to seek to prevent people from living in a way that meets their individual needs.

However, many LPAs have local plan policies that restrict or control flat conversions, particularly in suburban areas characterised by family housing. These policies commonly:

Seek to protect larger family homes from subdivision where there is a demonstrable need for such homes in the area.
Set minimum floor area standards for the resulting flats — often with reference to the nationally described space standard.
Require adequate amenity space for each flat — private or communal garden space, particularly for ground floor units.
Set standards for car parking and cycle storage.
Require that the external appearance of the building is not materially harmed.

Your statement must engage directly with your LPA's specific policies on flat conversions. These vary significantly between authorities.

What your supporting statement should cover

The principle of conversion — housing mix and need

This is often the primary policy test. Where the LPA has a policy protecting larger family homes, your statement should:

Establish the current size and use of the property — number of bedrooms, floor area, layout — and explain whether it genuinely functions as a family home or has already been subdivided informally.
Address any local housing needs evidence that supports the delivery of smaller units — for example, evidence of high demand for one and two-bedroom flats in the area, high housing costs making family homes inaccessible to younger people, or an identified surplus of large dwellings.
Explain the housing mix proposed — number of flats, bedroom numbers, and floor areas — and how this addresses identified local need.

Design and external appearance

Flat conversions frequently involve external alterations — additional entrance doors, new windows, extraction vents, bin stores, and cycle storage. Your statement should confirm that:

External alterations are minimal and sympathetic to the character of the host building and the street.
New openings, if any, respect the established fenestration pattern of the building.
Materials match or complement the existing building.
Bin and cycle storage is provided in a manner that does not harm the appearance of the frontage.

Internal layout and space standards

The internal layout must provide each flat with adequate floor area, natural light, ventilation, and storage. Your statement should confirm:

The floor area of each flat and how this compares with the nationally described space standard or any local minimum standard.
That each flat has adequate natural light and outlook from habitable rooms.
That sound insulation between flats will be provided to the relevant Building Regulations standard (Part E).
The layout of shared areas — entrance, stairs, and corridors — and how these will be managed.

Amenity space

LPAs commonly require each flat to have access to a reasonable area of private or communal amenity space. For ground floor flats, a private garden area is often expected. Your statement should confirm what amenity space is provided for each flat and how this meets any applicable standards.

Parking and highways

The change from a single dwelling to multiple flats will increase the potential demand for parking. Your statement should confirm how many parking spaces are provided, how this meets the LPA's parking standards for the number of flats proposed, and — where parking is constrained — explain the sustainable transport context and proximity to public transport.

Neighbour amenity

An increase in the number of occupants on a site can raise amenity concerns for neighbours. Address noise, comings and goings, and the management of shared areas. Where an extraction system, air source heat pump, or other mechanical plant is proposed, confirm that noise levels will be acceptable.

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