Can a neighbour block a Prior Approval extension in London?

A neighbour cannot block Prior Approval, but they can submit representations to the LPA during the 21-day consultation period. The council can only refuse if it determines the impact on adjoining premises would be materially detrimental — the threshold is higher than in a full planning application, where design, character, and amenity are all material considerations. Overlooking, loss of daylight, and visual impact from the immediate neighbour's perspective are the relevant objection grounds.

What is the maximum rear extension size under Prior Approval in London?

8m from the original rear wall for a detached house; 6m from the original rear wall for a semi-detached or terraced house. The 'original rear wall' means the rear wall of the original dwelling as it was built — not as extended by previous works. If a previous owner has already built a 2m rear extension, any Prior Approval extension is measured from the original rear wall, not the extended wall — but the existing extension may use some of the permitted development volume allowance independently.

Does Prior Approval apply to flats or converted houses in London?

No — Prior Approval for larger extensions applies only to houses. Flats, apartments, converted houses split into flats, and HMOs (houses in multiple occupation) are not eligible. Many London Victorian terraces have been converted to flats — if your property is a converted flat or any part of the building is used as a separate dwelling, the Prior Approval route is not available.

How long does a Prior Approval application take in London?

The statutory determination period is 42 days from the date of acknowledgement of the valid application. If the council does not determine within 42 days, prior approval is deemed granted. In practice, most London boroughs determine Prior Approval applications within 4–6 weeks. The Builderr project management team coordinates Prior Approval submissions and tracks the 42-day determination window.

Prior Approval Larger Home Extension London 2025 | Neighbour Consultation Scheme

What Is Prior Approval for a Larger Home Extension in London?

Prior Approval for a Larger Home Extension (Householder Prior Approval) allows single-storey rear extensions up to 8m on a detached house and 6m on a semi-detached or terraced house in London — beyond the standard 3m/4m permitted development limits. You notify the council, neighbours are consulted for 21 days, and the council determines whether the extension would be 'materially detrimental' to neighbours. No fee is required. The process takes 42 days.

Prior Approval for Larger Home Extensions: eligibility, limits and how to apply

The Householder Prior Approval procedure (Class A.1 of Part 1 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015 as amended) allows homeowners to build a single-storey rear extension beyond the standard permitted development size limits — up to 8m from the original rear wall for detached houses, and up to 6m for semi-detached and terraced houses — without requiring a full planning application. This temporary measure (introduced in 2013, made permanent in 2019) significantly increases the size of extension that can be built in many suburban London boroughs. Eligibility conditions: the extension must be single-storey only; the extension must not exceed 4m in height at the eaves; the property must be a house (not a flat, HMO, or converted dwelling); the works must not be within a Listed Building, a Site of Special Scientific Interest (SSSI), or in a National Park; the extension must not extend beyond the side elevation of the original dwelling; materials must be similar in appearance to the existing house; and the extension must not shade a neighbour's property in a way that is materially detrimental. The prior approval application is submitted to the local planning authority on a specific form (available from the Planning Portal). There is no application fee for a Householder Prior Approval application. The notification triggers a 21-day public consultation period during which adjoining owners and occupiers (and any others the council considers appropriate) can submit representations. After the 21-day consultation period, the council has 42 days from the date of the application to issue its decision. If the council does not issue a decision within 42 days, the prior approval is deemed granted. The test for refusal is narrow: the council can only refuse if it determines that the impact on the amenity of adjoining premises (primarily overlooking, loss of daylight/sunlight, and visual impact from adjoining properties) would be materially detrimental. Policy grounds such as design quality, sustainability, or character of the area are not relevant considerations for the prior approval test.

How Prior Approval differs from standard permitted development and full planning

Prior Approval sits between standard permitted development (no notification required, no neighbour consultation) and full planning permission (full policy assessment, 8-week determination, permitted development rights can be refused on policy grounds) in both process and risk profile. Under standard permitted development (Class A, up to 3m depth for a terrace, up to 4m for a semi or detached), no application to the LPA is required — works can proceed immediately subject to Building Regulations. Under Prior Approval, a formal notification is required and the council has 42 days to object based on neighbour impact. This means Prior Approval is not as fast or certain as standard PD, but significantly faster and simpler than a full planning application. Key practical differences in London: in Article 4 designation areas (conservation areas in inner London — Hackney, Islington, Camden, Hammersmith and Fulham, Kensington and Chelsea, Wandsworth), standard PD rights for rear extensions are removed, but Prior Approval Class A.1 rights are not removed by an Article 4 Direction — meaning the Prior Approval route remains available even in Article 4 conservation areas where a 4m extension (single-storey) would otherwise require full planning. This is a significant practical benefit for homeowners in inner London conservation areas seeking a larger extension than a standard PD would allow. Combinations with other structures: Prior Approval for a larger extension can be combined with a side infill extension (up to 3m wide, single-storey, not in a conservation area and not a terrace) to create an L-shape or wrap-around plan, subject to both sets of conditions being met independently. Prior Approval does not override the need for Building Regulations approval — a Building Notice or Full Plans Approval from building control is still required regardless of whether the extension is under PD, Prior Approval, or full planning.