Do I need planning permission to convert a house into flats?

Splitting a house into separate flats is a material change of use in planning law: section 55(3)(a) of the Town and Country Planning Act 1990 treats the use of a single house as two or more separate homes as development. There is no permitted development route for it, so a full planning application is needed.

What the council checks

• Flat sizes. London councils apply the nationally described space standard. A one-bedroom flat for two people needs at least 50 sq m, a two-bedroom flat for four people 70 sq m, and a three-bedroom flat for five people 86 sq m. A double bedroom must be at least 11.5 sq m.
• The original house. Many boroughs protect family houses. Some set a minimum original floor area before a conversion is allowed (Hillingdon, for example, asks for 120 sq m), or require at least one family-sized flat with a garden.
• Outdoor space, refuse and cycle storage, and the effect on neighbours: noise, overlooking and parking pressure.
• Local limits. Some councils cap the share of converted houses in a street.

Building regulations

The conversion also needs building regulations approval. The main points are fire separation between flats and a protected escape route, sound insulation between floors and walls, and separate services. We draw these with the structural calculations, so the package is ready for building control and for builders to price.

How we approach it

We check the borough's policies and the planning history of the street before designing, then test the layout against the space standards. Our flat conversions page explains the drawings we prepare.

Sources

• Town and Country Planning Act 1990, section 55 (legislation.gov.uk)
• Technical housing standards: nationally described space standard (gov.uk)
• Hillingdon Local Plan Part 2, policy DMH 4 (Hillingdon Council)

Related services

• Planning permission: We prepare and submit your application, deal with the planning officer, and keep you informed until there's a decision.
• Building regulations drawings: Clear construction drawings and a specification your builder can price from, submitted to building control for you.
• Structural calculations: Structural drawings and calculations for building control, designed by engineers within the Green Code group and coordinated with your drawings.
• Flat conversions: Drawings and applications for converting a house into flats, or reconfiguring existing flats, for owners and landlords.