Home/Can I Build an Extension Without Planning Permission in London? (2026 Guide)

2026 Guide

Can I Build an Extension Without Planning Permission in London? (2026 Guide)

Permitted Development rights let many homeowners extend without planning permission — but London is different. Boroughs like Hackney, Camden, and Westminster use Article 4 Directions to restrict those rights, meaning the answer depends entirely on your property and your street.

The answer to this question is never automatic in London. While Permitted Development (PD) rights exist in law, your borough, your street, and your property type can each remove them. This guide explains the exact rules in force for 2026, the most common London-specific restrictions, and how to check what applies to your specific address before spending money on drawings.

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When it may be permitted development

These are the common features that keep a project on the simpler route.

Rear Extensions (standard): Single-storey extensions up to 3m depth for terraced and semi-detached houses, or 4m depth for detached houses. The eaves height must not exceed 3m and the overall height must not exceed 4m.

Larger Home Extensions (prior approval): Under the Neighbour Consultation Scheme, terraced and semi-detached houses can extend up to 6m and detached houses up to 8m, provided no neighbour objects and the council grants prior approval. This route requires a formal notification before work begins.

Loft Conversions: Up to 40m³ of additional roof space for terraced houses, and up to 50m³ for detached and semi-detached houses. The conversion must not project beyond the slope of the existing roof facing a highway.

Side Extensions: Single-storey only, with a width no more than half the width of the original house. Two-storey side extensions are not permitted under PD.

Outbuildings and Garden Rooms: Single-storey outbuildings are generally PD if they cover less than 50% of the curtilage, sit no higher than 2.5m within 2m of a boundary, and are not used as a primary dwelling.

When planning permission is more likely

These are the usual triggers that push a scheme beyond straightforward PD rights.

Flats and Maisonettes: Standard PD rights for extensions do not apply to flats or maisonettes — converted or purpose-built. A full planning application is required regardless of scale.

Conservation Areas: Over 1,000 Conservation Areas exist across London. Within them, side extensions, roof alterations (dormers), and cladding changes are removed from PD — a full planning application is needed. Even modest changes to front elevations often require permission.

Article 4 Directions: Councils can and do withdraw specific PD rights via Article 4 Directions. Islington has removed side and rear PD rights across significant parts of the borough. Southwark and Richmond apply Article 4s to control HMO conversions and frontage alterations. Always check your specific address.

Listed Buildings: Any works that affect a listed building or its curtilage require Listed Building Consent in addition to, or instead of, planning permission. PD rights are effectively suspended. London has over 19,000 listed buildings — more than any other English city.

Previous Extensions Have Used the Allowance: PD volume limits are calculated against the 'original dwellinghouse' — the building as it stood on 1 July 1948, or as built if constructed later. If a previous owner already extended, that volume counts against the limit and you may have no remaining PD allowance.

Two-Storey Rear Extensions: Two-storey rear extensions are not standard PD and almost always require a full planning application, particularly where they could affect neighbouring amenity or privacy.

What CanUBuild checks

Faster answers before you speak to an architect or builder

The tool is designed to answer the first question most homeowners have: is this worth pursuing, and what is most likely to block it?

Address-Level Constraints: We check whether your specific address sits in a Conservation Area, is a Listed Building, is in a Flood Zone, or is covered by an Article 4 Direction — the four designations most likely to remove or restrict your Permitted Development rights in London.

Nearby Planning Precedent: We pull real approved and refused planning decisions from properties close to your address. Seeing what the council has already accepted on comparable streets is one of the strongest indicators of how your application would be treated.

Permitted Development Eligibility: Based on your property type, extension dimensions, and the constraints at your address, we give you an instant assessment of whether your project is likely to fall within PD — or whether a full application is the route you need to take.

FAQ

Questions people ask before starting a project

What is the exact depth limit for a rear extension under Permitted Development?

For a single-storey rear extension: 3m for a terraced or semi-detached house, and 4m for a detached house. Under the Larger Home Extension (Neighbour Consultation Scheme), these limits increase to 6m and 8m respectively — but you must notify the council before starting work and no neighbour objections must be sustained. These limits assume the property is a house, not a flat, and that PD rights have not been removed.

Can I build a Permitted Development extension if I live in Hackney or Camden?

Possibly, but these boroughs are among the most restrictive in London. Camden covers large portions of its area with Conservation Areas and has supplementary design guidance that effectively constrains even PD works. Hackney has issued Article 4 Directions in several neighbourhoods. You cannot assume PD applies simply because your extension would be within the standard dimensions — you must check the specific constraints at your exact address.

What is the Neighbour Consultation Scheme (Larger Home Extension)?

Introduced in 2013 and made permanent in 2019, the Larger Home Extension scheme allows terraced and semi-detached houses to extend up to 6m (and detached houses up to 8m) at the rear under a prior approval process. You must submit a notification to the council, which then consults adjoining neighbours. If no objections are raised — or if objections are not sustained — the council issues prior approval and you can proceed. It does not apply in Conservation Areas or to properties where PD rights have been removed by an Article 4 Direction.

Do I need a Lawful Development Certificate even if I'm building under PD?

Yes — and it is strongly advisable in London. A Lawful Development Certificate (LDC) is a legal document issued by the council confirming that your build was lawful under PD at the time it was constructed. Without one, you may face difficulties when selling or remortgaging the property. Given the frequency of Article 4 Directions, Conservation Area boundaries, and previous-owner extensions in London, an LDC provides formal protection against any future challenge to the legality of the work.

Does a 2026 planning reform change anything for London extensions?

The government's 2025–2026 planning reforms are primarily focused on housebuilding targets, streamlining major development, and updating the NPPF. For individual householder extensions, the core PD rules — depth limits, volume limits, and the Article 4 Direction framework — remain unchanged going into 2026. Borough-level restrictions continue to apply, and London councils retain the power to issue Article 4 Directions. The most important variable for any London homeowner is still the constraints specific to their address.

Next step

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