What size rear extension is allowed under Permitted Development?

Under standard PD rights, a single-storey rear extension can be up to 3m deep on a semi-detached or terraced house, or 4m deep on a detached house. The maximum height is 4m. Under the Neighbour Consultation Scheme (sometimes called Prior Approval), these limits extend to 6m for semi-detached and terraced houses and 8m for detached. Double-storey rear extensions are capped at 3m depth and must be at least 7m from the rear boundary.

Is a side return extension covered by Permitted Development?

A pure side return extension — filling in the passage alongside the house — is treated as a side extension under PD rules. Side extensions under PD must not exceed half the width of the original house and cannot be forward of the principal elevation. In practice, most London side return extensions are narrow enough to fall within PD, but the rules are more nuanced than rear extensions and the exact configuration matters. Always get a Certificate of Lawful Development to confirm.

Do conservation areas affect Permitted Development rights?

Yes, significantly. In a conservation area, Permitted Development rights are automatically restricted for certain works — including cladding any exterior wall, adding a side extension, and altering the roof. Where an Article 4 Direction also applies (common across most inner London conservation areas), further PD rights are removed, often including rear extensions and dormers. If your property is in a conservation area, assume you need planning permission and verify the exceptions, rather than the other way around.

What is a Certificate of Lawful Development and do I need one?

A Certificate of Lawful Development (CLD) is formal confirmation from the council that your proposed works fall within Permitted Development and do not require planning permission. It is not legally required to build — PD rights exist regardless. But a CLD is strongly recommended: it protects you when you sell, confirms the position with mortgage lenders, and provides certainty that the council will not later challenge the works. Council fee in England: £258 for a householder CLD application.

Extensions

Permitted Development Rules for Extensions in London 2026: What You Can Build Without Planning Permission

Q: What is Permitted Development?

Permitted Development (PD) is a set of national planning rights that allow homeowners to carry out certain building works without needing a planning application. The rights are set out in the Town and Country Planning (General Permitted Development) (England) Order 2015 and cover extensions, loft conversions, outbuildings and more — subject to size limits and conditions. Local councils can restrict PD rights in conservation areas and other sensitive zones using Article 4 Directions.

What can you build under Permitted Development in London in 2026? This guide covers rear extensions, side returns, loft conversions and outbuildings — with the exact size limits and when they don't apply.

By Vladimir Castravet·14 May 2026

Permitted Development rights let you build extensions, loft conversions and outbuildings without a planning application — but the rules are specific and the exceptions matter. Getting this wrong costs time and money. Getting it right means you can start work months earlier.

This guide covers the 2026 position for London homeowners.

What Is Permitted Development?

Permitted Development (PD) is a national planning consent granted by Parliament — not the council. The Town and Country Planning (General Permitted Development) (England) Order 2015 sets out what can be built, and to what size limits, without a planning application.

The key word is “without a planning application.” PD rights exist automatically. You do not apply for them. What you can apply for — and what we strongly recommend — is a Certificate of Lawful Development, which is the council’s written confirmation that your specific project falls within PD.

Rear Extensions: The Rules

Standard Permitted Development limits (single-storey)

| Property Type | Maximum Depth | Maximum Height | Notes | |---|---|---|---| | Terraced house | 3m | 4m | Eaves must not exceed 3m | | Semi-detached house | 3m | 4m | Eaves must not exceed 3m | | Detached house | 4m | 4m | Eaves must not exceed 3m |

Neighbour Consultation Scheme (Prior Approval)

The Neighbour Consultation Scheme extends PD limits for single-storey extensions only:

| Property Type | Extended Limit | |---|---| | Terraced or semi-detached | Up to 6m depth | | Detached | Up to 8m depth |

Under this route, you submit a Prior Approval application to the council (fee: £258). The council notifies your neighbours; if they raise no objection, Prior Approval is confirmed and you can build. If objections are raised, the council assesses the impact on neighbours. This is not a full planning application — the council cannot refuse on design grounds, only on impact on amenity.

Double-storey rear extensions

A double-storey rear extension falls within PD provided:

Maximum 3m depth from the original rear wall
At least 7m from the rear boundary
The upper floor does not include side-facing windows (or they are obscure-glazed and non-opening)
The roof pitch matches the existing house

Double-storey side extensions do not fall within PD — they require full planning permission.

Side Return Extensions

A side return extension (filling in the passage alongside the ground floor) is treated as a side extension under PD rules. The PD conditions for side extensions are stricter than for rear extensions:

Must not exceed half the width of the original house
Must not be forward of the principal elevation (i.e., cannot project toward the street)
Must be single-storey to use PD (maximum 4m height)
In conservation areas: side extensions under PD are automatically excluded — you need planning permission

Most London Victorian terraced side returns are 900mm–1.5m wide, which is typically within half the width of the original house. But the exact geometry matters — always confirm with a CLD rather than assuming.

When combined with a rear extension (an L-shape), the rear element follows rear extension rules and the side element follows side extension rules. Both must be within their respective PD limits for the combined project to be PD.

Loft Conversions Under Permitted Development

Loft conversions also fall within PD, subject to volume limits:

| Property Type | Maximum Additional Volume | |---|---| | Terraced house | 40 cubic metres | | Semi-detached or detached | 50 cubic metres |

Additional conditions:

No alteration to the roof slope on any elevation that fronts a highway
Any dormer must be set back at least 20cm from the eaves
Materials must be similar in appearance to the existing house
No balcony, verandah or raised platform

These volume limits apply to the total volume added across all loft works — if a previous owner has already added a dormer, the remaining allowance is reduced by that amount.

When Permitted Development Does NOT Apply

PD rights can be restricted or removed entirely in several circumstances:

Conservation areas Certain PD rights are automatically removed in conservation areas. Side extensions, roof cladding and other works visible from the highway require planning permission. Check whether your property is in a conservation area before assuming PD applies.

Article 4 Directions Councils can issue Article 4 Directions to remove specified PD rights in defined areas. In most inner London conservation areas, Article 4 Directions remove the right to add rear dormers, side extensions and in some cases rear extensions without full planning permission.

Listed buildings No PD rights apply to listed buildings (Grade I, II* or II). All works — including internal alterations — require Listed Building Consent in addition to any planning permission.

Flats and maisonettes PD rights for extensions and loft conversions apply only to houses. Flats and maisonettes have no PD rights for these works under Class A or B. Freeholders of purpose-built flats wishing to extend need full planning permission.

Conditions on the original planning permission Some houses were built with planning conditions that specifically remove PD rights. This is common on new developments from the 1980s–2000s. Check the original planning permission for any such conditions.

How to Confirm Your PD Status

The safest route is to apply for a Certificate of Lawful Development before starting work. This gives you:

Written confirmation that the works are lawful
Protection on resale (solicitors will ask)
Comfort for mortgage lenders
A clear record for building control

| Route | Council Fee | Typical Timeline | |---|---|---| | Certificate of Lawful Development | £258 | 6–8 weeks | | Prior Approval (Neighbour Consultation Scheme) | £258 | 6–8 weeks | | Full Planning Permission (householder) | £258 | 8–12 weeks | | Pre-application advice | £100–£300 | 4–8 weeks |

Note: From 6 December 2023, the planning application fee for householder applications in England increased to £258. This applies to CLDs, Prior Approval and full householder planning applications alike.

Article 4 Directions in London: Which Boroughs

Article 4 Directions restricting rear extensions, dormers or other works are in place across many inner London boroughs. The following boroughs have significant Article 4 coverage:

Royal Borough of Kensington and Chelsea — Almost the entire borough is covered by conservation area Article 4 Directions affecting roof works and rear extensions.
City of Westminster — Extensive conservation area and Article 4 coverage, particularly in Mayfair, Marylebone, Belgravia and Pimlico.
London Borough of Hammersmith and Fulham — Conservation areas in Fulham, Hammersmith and Shepherd’s Bush have Article 4 Directions for roof works.
London Borough of Wandsworth — Battersea conservation areas; most of SW11 and SW12 is standard PD.
London Borough of Richmond — Extensive Article 4 coverage in Kew, Richmond and Twickenham.
London Borough of Hounslow — Chiswick conservation areas have Article 4 for roof alterations.

Article 4 coverage changes. The definitive check is the council’s planning portal for your specific address — or ask your architect to confirm.

Costs Summary

| Item | Cost | |---|---| | Certificate of Lawful Development | £258 council fee + architect drawings (£800–£1,500) | | Prior Approval application | £258 council fee + drawings (£800–£1,500) | | Full Planning Application (householder) | £258 council fee + architect drawings (£2,500–£6,000) | | Pre-application advice | £100–£300 council fee | | Planning consultant (complex cases) | £1,500–£4,000 |

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