What can you legally build without planning permission?

The headline allowances for houses: rear extensions of 4 metres (detached) or 3 metres (other houses), extendable to 8 and 6 metres through prior approval; side extensions up to half the width of the original house; loft conversions adding up to 50 cubic metres (40 for terraces) with dormers on the rear; and garden buildings within the height and coverage limits.

Smaller works are generous too: porches up to 3 square metres and 3 metres high (at least 2 metres from a highway boundary), fences and walls up to 2 metres (1 metre beside a highway), solar panels, driveways in permeable materials, and most internal alterations, which aren't development at all.

Every allowance carries conditions — the 50% land coverage cap, matching materials, eaves and boundary height limits, nothing forward of the principal elevation. Permitted development is precise: a project 20 centimetres over a limit needs a full application just as surely as one twice the size.

The rights belong to houses. Flats and maisonettes have no householder permitted development, and designated land — conservation areas, national parks, AONBs, World Heritage Sites — loses cladding, side extensions and larger rear extensions, with listed buildings under a separate consent regime entirely. Article 4 directions can remove specific rights on specific streets, which is common in exactly the attractive Victorian areas where extension appetite is highest.

Remember the parallel track: permitted development only settles the planning question. Extensions, lofts and larger outbuildings still need building regulations approval, and boundary works can trigger the Party Wall Act.

Before relying on any of this, verify your specific address — previous extensions, constraint designations and Article 4 directions all change the answer, and they're exactly what a proper property check surfaces before you spend on design.