Do I Need Planning Permission to Convert a House into Flats in London? (2026)

Why converting to flats needs planning permission

Turning one house (Use Class C3) into two or more self-contained flats (still C3, but a different planning unit) is a material change of use, because you are creating additional separate dwellings. There is no permitted-development right that allows it, so a full planning application is required almost every time. The council assesses the principle of intensifying residential use on the site, the mix of unit sizes, and the effect on the character of the street and on neighbours. Whether the borough even supports conversions in that location is the first question the application has to answer. Many London boroughs apply a specific policy on the loss of family housing, resisting the subdivision of larger houses — often those with three or more bedrooms — because the borough is trying to protect its stock of family-sized homes. Others take the opposite view in the right location, welcoming additional smaller units near transport and town centres. The point is that the acceptability of a conversion is a policy judgement made borough by borough, and sometimes street by street, rather than a national right you can assume, so reading the local plan before committing to a scheme is not optional. A conversion that would sail through in one borough can be refused on principle a mile away.

The space and amenity standards flats must meet

Flat conversions are judged against minimum standards, and failing them is the most common reason for refusal. The nationally described space standard and the London Plan set minimum internal floor areas by number of bedrooms and occupants — for example a one-bed, two-person flat has a minimum floor area that a cramped conversion often cannot meet. Councils also look for adequate natural light and outlook to habitable rooms, private or shared amenity space, proper refuse and recycling storage, cycle parking, and sound separation. Many boroughs resist very small studios and poor-quality basement or single-aspect units. The nationally described space standard is specific: a one-bed, one-person flat must be at least 37 square metres, a one-bed, two-person flat at least 50 square metres, a two-bed, three-person flat at least 61 square metres, and a two-bed, four-person flat at least 70 square metres, with minimums rising further for larger households. It also sets a minimum floor-to-ceiling height of 2.3 metres for at least three-quarters of each flat, and requires built-in storage. On top of the floor areas, London boroughs typically want a reasonable proportion of dual-aspect homes, private outdoor space such as a balcony or garden share, and step-free access where the building allows. A conversion that meets the headline floor areas but produces dark, single-aspect rooms or has nowhere for bins and bikes will still struggle, because the standards are about the quality of the resulting homes, not just their square metres.

• Minimum internal floor areas (national space standard / London Plan)
• Natural light and outlook to habitable rooms
• Private or shared amenity space
• Refuse, recycling and cycle storage for each flat

The building regulations that make or break a conversion

Even with planning permission, a flat conversion lives or dies on building regulations, because you are creating separate dwellings that must be independently safe. Sound insulation between flats has to meet the Part E standard, usually needing upgraded floors and separating walls. Fire safety is critical: each flat needs proper fire separation and a protected means of escape, often a fire-rated common staircase and fire doors, with detection throughout. Each flat generally needs its own services and metering. These requirements shape the whole design, so the building-regs strategy has to be set at the concept stage, not bolted on later.

• Part E sound insulation between separate dwellings
• Fire separation and a protected means of escape
• Fire doors and linked detection throughout
• Separate services and metering per flat

What else affects a flat conversion?

Several other approvals and constraints commonly apply. If the building is a converted or leasehold property already, freeholder consent and lease terms may restrict the works. A conservation area or listed building adds design and consent requirements. Parking and highways policy can weigh against conversions in controlled parking zones. And once flats are created and occupied, council tax banding changes and, if let, the flats may fall within licensing. A realistic conversion scheme accounts for all of these rather than treating it as a purely internal job.

How do I confirm my house can be converted?

Four questions shape it: does the borough's policy support conversions in that location, can the layout meet the minimum flat sizes and amenity standards, can the building achieve Part E sound and fire separation, and are there lease, conservation or parking constraints. If the policy is supportive and the standards are achievable, a full planning application plus a full-plans building-regulations submission is the route. We test the layout against the borough standards early, so effort is not spent on a scheme that cannot meet the floor areas or the fire strategy.

How many flats can you get out of a London house?

The instinct is to squeeze in as many units as possible, but the number a house can sensibly be split into is set by the standards, not by ambition. Once you overlay the minimum internal floor areas, the requirement for adequate light, outlook and amenity space, and the fire-escape geometry a common staircase imposes, a typical London terraced or semi-detached house usually yields far fewer good flats than the raw floor area suggests. Boroughs actively resist over-intensified conversions that produce cramped, single-aspect or windowless units, so the realistic yield is whatever the standards allow at a quality the council will approve — not the maximum the walls could contain.