When Does a London House Extension Need Planning Permission in 2025?

Single-storey rear extensions — the standard PD limits in London: under Part 1, Class A of the General Permitted Development Order 2015, a single-storey rear extension on a dwelling house (a house — not a flat) qualifies as permitted development (no planning permission required) if it meets ALL of the following conditions: Maximum depth: attached (terraced or semi-detached) house: maximum 3.0m from the original rear wall of the house; detached house: maximum 4.0m from the original rear wall. Maximum height: no higher than 4.0m (to the highest point of the extension); and, if within 2m of the boundary: no higher than 3.0m (to the eaves). No side element: the extension does not include a side element extending beyond the side elevation of the original house. Materials: the materials of the external surfaces of the extension are the same as or similar in appearance to the existing house. Not on a Listed Building: listed buildings have no PD rights for extensions — listed building consent and planning permission are required for any extension to a listed building. In a conservation area: conservation areas in London do not automatically remove PD rights for rear extensions — a single-storey rear extension that meets the depth and height limits above is PD in a conservation area (PROVIDED the extension does not come within 2m of the boundary and exceed 3m eaves height). However, some London boroughs have Article 4 Directions that specifically withdraw PD rights for certain types of development in specific conservation areas — including rear extensions. Check the local borough's Article 4 Directions before assuming PD applies in a conservation area. The Prior Approval (larger home extension) scheme — extended PD limits for single-storey rear extensions: the Prior Approval scheme allows single-storey rear extensions larger than the standard PD limits, subject to a Prior Approval process: maximum depth under the Prior Approval scheme: attached (terraced or semi-detached) house: up to 6.0m from the original rear wall; detached house: up to 8.0m from the original rear wall. The Prior Approval scheme is NOT available in Article 4 Direction areas (where PD rights have been withdrawn). The Prior Approval process: the homeowner (or agent) submits a Prior Approval application to the local planning authority (LPA). The LPA has 42 days to determine the application. The LPA consults adjoining neighbours during the 42-day period — if no objections from adjoining owners are received, Prior Approval is deemed granted (or the LPA may issue a formal Prior Approval decision). If neighbours object, the LPA must consider whether the extension will have an unacceptable impact on the amenity of the adjoining neighbour (overshadowing, loss of light) — this is the sole test for Prior Approval under the larger home extension scheme. Prior Approval fees: £120 for a Prior Approval application (2025). Important definitions for PD calculations: the 'original house': for PD calculation purposes, the 'original house' is the house as it was on 1 July 1948 (the date the Town and Country Planning Act 1947 came into force) — or as it was first built if it was built after 1 July 1948. Any extensions built to the house since 1 July 1948 are NOT part of the 'original house' for PD purposes. This means: if the rear of a London Victorian terrace has already been extended by 2m since 1948, the maximum further extension depth under standard PD is only 1m (to reach the 3m maximum from the original rear wall). If the house has ALREADY reached or exceeded the standard PD limit, the Prior Approval scheme may still be available — but the total depth (including the existing extension) must not exceed 6m (attached) or 8m (detached). Conservation areas: PD rights for rear extensions are generally available in conservation areas subject to the standard limits. Article 4 Directions (which specifically withdraw PD rights in named areas) are more restrictive — check the borough.

Double-storey rear extensions in London — when is planning permission required: a two-storey rear extension (a rear extension that extends the first floor as well as the ground floor) is NOT permitted development if: it is closer than 7m to the rear boundary; OR the total height exceeds the height of the existing house; OR it includes a side element extending beyond the original side elevation; OR it is within 2m of the boundary; OR it is in an Article 4 Direction area. A two-storey rear extension that meets all the PD limits (depth: maximum 3m for attached, 4m for detached; not within 7m of the rear boundary; height not exceeding house height; materials matching the existing house) is PD. In practice, most urban London Victorian terraces (which have rear gardens of 6m-12m depth) have rear boundaries within 7m of the existing rear wall — meaning a double-storey extension is typically NOT permitted development for most London terraced houses. For these properties, a full planning application (Householder Application) is required for a two-storey rear extension. Side extensions in London — PD rules: side extensions are generally more restricted under PD than rear extensions. A single-storey side extension is PD if: it does not extend beyond the side elevation of the principal elevation; the width of the extension is no more than half the width of the original house; the height does not exceed the height of the original house; it is not in a conservation area where Article 4 removes PD for side extensions; it does not extend beyond the side elevation on the principal elevation side. A two-storey side extension is NOT permitted development in a designated area (conservation area, National Park, AONB, SSSI) — and requires planning permission. In most London conservation areas, side extensions (particularly those extending the full height of the property to match the ridge) are likely to require planning permission and are subject to the local conservation area design guidance. Wrap-around extensions (rear + side combined in a single L-shaped scheme): a combined rear and side extension that is submitted as a single scheme is assessed as a whole — if the side element exceeds the PD limit for side extensions, the whole scheme requires planning permission. Flats and maisonettes: PD rights do NOT apply to flats or maisonettes. Any extension to a flat or maisonette requires a full planning application. In London, many Victorian terrace houses have been converted into flats — where the building is a converted flat (not an original purpose-built dwelling house), the building loses its dwelling house PD rights for the common parts. Individual leaseholders in a converted flat do not have PD rights to extend the building. Purpose-built blocks of flats also have no PD rights for extensions. This is a common source of confusion — always confirm whether the building is a dwelling house or a flat before assuming PD applies. Article 4 Directions in London — what they are and which London boroughs use them most: Article 4 Directions (Article 4(1) of the GPDO 2015) are directives issued by the local planning authority that withdraw specific PD rights in a defined area — requiring planning permission for works that would normally be PD. In London, Article 4 Directions are commonly used to: withdraw PD rights for rear extensions in conservation areas (requiring planning permission for any rear extension in specific conservation areas); withdraw PD rights for changes of use (e.g., removing the right to convert a house to an HMO without planning permission); withdraw PD rights for loft conversions with dormers on particular streets. London boroughs with significant Article 4 Directions coverage: Camden; Islington; Kensington and Chelsea; Hammersmith and Fulham; Westminster; Hackney; Southwark (selected conservation areas). To check Article 4 Directions: contact the local planning authority directly; check the borough's planning portal or interactive planning map; speak to an architect or planning consultant familiar with the specific borough.

When a full planning application is required — summary of when PD does NOT apply and a full application is needed: a two-storey rear extension within 7m of the rear boundary (most urban London terraces); a side extension exceeding 50% of the original house width; any extension to a flat or maisonette; any extension to a listed building; any extension in an Article 4 Direction area (where the specific PD right has been withdrawn); any extension that exceeds the standard PD depth, height, or position limits; any front extension (extending the front of the house towards the highway — almost never PD). Type of planning application for London house extensions: Householder Application: the standard planning application for single-dwelling extensions, alterations, and outbuildings. Used for: all house extensions requiring planning permission; loft conversions requiring planning permission; garage conversions requiring planning permission; outbuildings requiring planning permission. Application fee (2025): £258 for a single dwelling house application. Determination period: 8 weeks (statutory period for a Householder Application). What is submitted with a Householder Application: completed application form (via the Planning Portal — www.planningportal.co.uk); existing and proposed drawings (plans, elevations, and sections — typically produced by an architect or designer); a site location plan (1:1250 scale, showing the application site in relation to surrounding streets); a site plan (1:500 scale, showing the application site boundaries); a design and access statement (for conservation area applications and larger schemes; for straightforward Householder Applications in non-conservation areas, a design statement is not always required — check with the borough); a heritage impact assessment (for listed buildings or significant conservation area proposals). Full Application: used where the scheme is more complex or where a Householder Application is not appropriate (e.g., a change of use, commercial development, or development exceeding the Householder threshold). Fee: variable (£578 for a change of use; larger fees for commercial or multi-unit development). Consultation process: the LPA will consult adjacent neighbours during the 8-week determination period (or longer for complex applications). Neighbour comments (representations) are a material consideration but are not determinative — an objection from a neighbour does not automatically lead to refusal if the proposal complies with relevant planning policies. The LPA officer assesses the application against the Local Plan policies, the London Plan policies (where relevant — the London Plan is a strategic planning framework for Greater London), the London borough's supplementary planning guidance for residential extensions, and relevant national planning policies (NPPF — National Planning Policy Framework). Approval rates for London householder applications: the vast majority of householder applications for well-designed extensions in London are approved — approval rates for householder applications are typically 85-95% across most London boroughs. Refusal rates are highest where: the extension is in a conservation area and is not in keeping with the character of the area; the extension would cause significant harm to the amenity of adjoining neighbours (overshadowing, loss of privacy, loss of light); the extension significantly exceeds the policies in the local area guidance. Pre-application advice: many London boroughs offer a pre-application advice service for householder proposals — typically £150-£900 for written pre-application advice from the planning officer. Pre-application advice helps confirm: whether planning permission is required; whether the proposal is likely to be acceptable in principle; what information and documents are required for the application; any specific design issues to address before submitting. Pre-application advice is strongly recommended for: extensions in conservation areas; larger or more complex schemes; schemes where the PD position is unclear; listed building proposals.