Do flats have permitted development rights?

Flats and maisonettes don't have householder permitted development rights, so extensions, loft conversions, porches and garden buildings all need planning permission. But some smaller projects, such as fences, gates and solar panels, are covered by other rights that apply to flats too.

Why flats are different

The householder rights in the General Permitted Development Order (Schedule 2, Part 1) apply to a "dwellinghouse", and the Order defines a dwellinghouse as excluding a building containing flats, or a flat within one. So a ground floor flat with its own garden has no right to build a rear extension or garden room without planning permission, even if an identical house next door does.

Maisonettes count as flats for this purpose. A house converted into flats loses its householder rights too.

What needs planning permission

Rear and side extensions, including conservatories.
Loft dormers and other roof extensions.
Porches.
Sheds, garden rooms and other outbuildings.

What flats can still do

Walls, fences and gates (Part 2, Class A) apply to any building, so the same 1m and 2m height limits apply to flats. See the limits.
Solar panels (Part 14, Class A) expressly cover blocks of flats as well as houses, with similar limits. See the limits.

In both cases, a leasehold flat usually needs the freeholder's or management company's consent under the lease as well, which is a separate matter from planning.

Building regulations

Building regulations apply to flats in the same way as houses. Work affecting fire separation between flats, such as new doors onto a shared hallway, is closely controlled.