Do I need planning permission? A London checker

The three routes, and what each costs

Permitted development, confirmed with a Lawful Development Certificate

Permitted development means the national rules already grant permission, so there is no planning application. I still recommend a Lawful Development Certificate (LDC): it costs£274 for proposed work (half the householder fee), should be decided within 8 weeks of validation, and gives you the paper a buyer’s solicitor will ask for. Building without one is lawful if the scheme really complies, but you carry the risk if it turns out not to.

Larger home extension prior approval

A single-storey rear extension between 3 and 6 metres deep (4 to 8 metres on a detached house) can go through prior approval instead of a full application, if the house is not on conservation area or other protected land. It costs £249. The council notifies the neighbours and has 42 days to decide; you cannot start until it approves or the 42 days pass without a decision.

Householder planning application

Everything else: anything over the limits, side and two-storey extensions in conservation areas, mansards, front dormers, most new basements, and almost all external work to flats. The fee is£548 in England from 1 April 2026; a draft regulation proposes £575 for applications made on or after 8 December 2026. The target decision time is 8 weeks from validation. How long that really takes borough by borough is inhow long planning permission takes in London.

Separate from planning: Building Regulations, party walls and listed building consent

Whatever the planning route, an extension, loft or basement needs Building Regulations approval (see building control fees in London), and work on or near a shared wall needs party wall notices: at least two months before work on the wall itself, one month for excavation near a neighbour’s foundations. A listed building needs listed building consent for alterations that affect its character; there is no application fee for it. For the detail behind the rules, read the permitted development guide for London boroughs, planning for side-return extensions and loft conversion planning.

How this checker works

It applies the limits in Classes A (extensions), B (roof enlargements) and C (other roof alterations) of Part 1 of Schedule 2 to the General Permitted Development Order 2015, as in force on 6 October 2026, to the answers you give. Conservation areas count as article 2(3) land, which removes side extensions, two-storey rear extensions, the larger 6 and 8 metre route and all Class B roof enlargements. "Not sure" answers never return a permitted development result: they return "check with the council". Basement answers follow the Planning Portal’s guidance and the borough-wide basement Article 4 directions in Hammersmith & Fulham, Kensington & Chelsea and Westminster. Fees are the England fees from 1 April 2026.

1. legislation.gov.uk — GPDO 2015, Schedule 2, Part 1 (householder permitted development): Class A (extensions): 3 m / 4 m single-storey rear limit, 6 m / 8 m with prior approval (not on article 2(3) land), 4 m height, 3 m eaves within 2 m of a boundary, side extensions single storey and no wider than half the original house, two-storey 3 m deep and 7 m from the rear boundary, A.2 conservation area exclusions. Class B (roof enlargements): 40 m³ terrace / 50 m³ other, nothing beyond the front roof slope, not on article 2(3) land.
2. GOV.UK — Permitted development rights for householders: technical guidance: Householder rights do not apply to flats or maisonettes; "original" means as at 1 July 1948 or as first built.
3. Planning Portal — Lawful Development Certificate: Proposed use or operation: half the normal planning fee. "Should be decided within 8 weeks", starting once the application is validated.
4. Planning Portal — Fees for Planning Applications in England (from 1 April 2026): Householder application £548; larger home extension prior approval £249; LDC (proposed) half the full fee.
5. legislation.gov.uk — Explanatory Memorandum, draft Planning Fees (Amendment and Transitional Provision) Regulations 2026: Draft: householder fee proposed to rise from £548 to £575 for applications made on or after 8 December 2026.
6. Planning Portal — Basements: planning permission: Converting an existing basement: permission unlikely unless a lightwell, new unit or external change. Creating a new basement "will commonly require planning permission".
7. GOV.UK — The Party Wall etc. Act 1996: explanatory booklet: Notice at least two months before work to an existing party wall; one month before excavating near a neighbour’s foundations or building a new wall on the boundary. No reply within 14 days = a dispute, and surveyors are appointed.
8. GOV.UK — Building regulations approval: how to apply: Full plans: decision within 5 weeks, or 2 months with your consent. Building notice: start 2 days after submitting. Completion certificate usually within 8 weeks of completion.

Guidance only. It does not cover trees, highways, flood risk, listed building detail, covenants, freeholder consent or every design condition. Get an LDC or speak to the council before you build.