Why Permitted Development Doesn't Apply to Flats

The short answer

Most of the permitted development (PD) rights that homeowners rely on — rear extensions, loft conversions, outbuildings, porches — apply only to a dwellinghouse. In planning law, a flat or maisonette is deliberately excluded from this definition.

That means if you own a flat, you generally cannot use permitted development to carry out alterations. You'll need to apply for planning permission instead, even for work that a neighbouring house could do without any application at all.

Why the law treats flats differently

The rules that grant householder PD rights are written specifically for houses. The legislation defines the works allowed to a "dwellinghouse" and then states clearly that this does not include a building containing one or more flats, or a flat contained within such a building.

There are practical reasons for this:

• Shared structure. Work to one flat can affect the walls, floors, roof and drainage of others. PD is designed for buildings under single ownership and control.
• Cumulative impact. Allowing every flat in a block to extend freely would be difficult to manage and could quickly change the whole building.
• Amenity for neighbours. Flats often sit close to other homes, so councils want the chance to assess each change.

What leaseholders and flat owners need instead

If permitted development is off the table, your route is usually a full planning application (or a householder application where the council accepts one for the works). Key points:

• Planning permission is the main consent you'll need for extensions, changes of use, or external alterations.
• Building regulations approval is separate and still applies to the structural and safety side of the work.
• Freeholder consent and your lease matter too. Even with planning permission, most leases require the freeholder's written permission before you alter the flat. Planning approval does not override your lease.
• Change of use — such as splitting a house into flats, or merging flats — needs planning permission in its own right.

Statutory determination targets for planning applications are set nationally (commonly discussed as an 8-week target for minor applications), but actual timescales vary. Fees also vary and are reviewed periodically. Check your borough page at /boroughs or compare performance at /league-tables.

Common misconceptions

• "I own the freehold, so PD applies to my flat." No — the exclusion is about the type of dwelling, not who owns it.
• "A maisonette isn't a flat." For PD purposes, maisonettes are treated like flats and are excluded.
• "My neighbour did it under PD, so I can too." They may live in a house. The same rights do not transfer to flats.
• "Small internal changes are always fine." Internal works may not need planning permission, but external changes and changes of use usually do, and your lease may still require consent.
• "Prior approval is the same as PD for flats." Prior approval routes are limited and specific; they don't restore general householder PD rights to flats.

This is general information and not legal advice. Rules, fees and timescales differ between areas, so always confirm the position with your borough before starting work.