Key facts at a glance

  • PD allows rear extensions up to 6m (semi/terrace) or 8m (detached via Prior Approval)
  • Loft conversions: max 40 m³ (terrace/semi) or 50 m³ (detached) added volume
  • Flats have NO Permitted Development rights for external work
  • Article 4 Directions can remove PD in specific London areas
  • Conservation areas restrict PD for side extensions, dormers, and cladding
  • Always get a Lawful Development Certificate (£129) for proof of lawfulness

IMAGE PLACEHOLDER -- infographic showing the key Permitted Development size limits for London houses

What is Permitted Development?

Permitted Development (PD) rights are automatic planning permissions granted by the government through the Town and Country Planning (General Permitted Development) (England) Order 2015 (the GPDO), as amended. They allow homeowners to carry out specified types of building work without submitting a planning application to the council, provided the work meets detailed conditions and size limits set out in the Order.

The GPDO is divided into Parts and Classes. For residential homeowners in London, the key ones are:

Each Class comes with a set of specific conditions, limitations, and restrictions. If your project fails to meet any of these, it falls outside PD and requires a full planning application. There is no partial compliance -- you either meet every condition or you need planning permission.

PD rights apply only to houses (Use Class C3). Flats, maisonettes, HMOs, and commercial properties have no PD rights under Part 1. If you live in a flat, skip to our section on flats below.

Class A: rear and side extensions

Class A is the most commonly used PD right in London. It covers single-storey and two-storey extensions to houses, both to the rear and to the side.

Single-storey rear extensions

The maximum depth a single-storey rear extension can project from the original rear wall of the house depends on the house type:

The "original rear wall" means the rear wall as it existed on 1 July 1948, or as originally built if the house was constructed after that date. If a previous owner built a rear extension, that previous extension counts against your PD allowance. This is a common trip-up -- if the house already has a small rear addition that was built before you bought it, you may have less PD depth remaining than you think.

Height limits

Other conditions

Two-storey rear extensions

Two-storey rear extensions have tighter limits under PD:

Side extensions

Side return extensions -- infilling the narrow alley along the side of a terraced house -- are a hugely popular way to enlarge a London kitchen. They typically fall within PD limits as they are usually single-storey and do not extend beyond the existing rear wall. See our complete side return extension guide for costs and details.

Prior Approval: the Larger Home Extension scheme

The Larger Home Extension scheme (technically called Prior Approval under Part 1, Class A, paragraph A.4) allows larger single-storey rear extensions than the standard PD limits, subject to a notification process.

How it works

  1. You submit a Prior Approval application to the council (fee: £120 in 2026).
  2. The council notifies adjoining neighbours by letter.
  3. Neighbours have 21 days to respond with any objections.
  4. If no objections are received, the council issues Prior Approval. If objections are received, the council assesses whether the impact on the amenity of neighbouring properties is acceptable.
  5. The council must determine the application within 42 days. If they fail to respond, Prior Approval is deemed granted by default.

Size limits under Prior Approval

All other PD conditions still apply (height, materials, 50% garden coverage, etc.). The scheme was made permanent in 2019 and remains in full effect in 2026.

Prior Approval is an excellent route for London homeowners who need a deeper single-storey extension than standard PD allows. It is faster and cheaper than a full planning application, and the council can only assess the impact on neighbouring amenity -- they cannot refuse on design, policy, or character grounds.

We prepare Prior Approval applications and drawings as part of our Essentials package (from £840). The process is straightforward, but the drawings must be accurate and the notification requirements precisely followed.

Class B: loft conversions and dormers

Loft conversions are one of the most common uses of PD rights in London. Class B allows additions or alterations to the roof of a dwellinghouse, including dormer windows, provided the following limits are met:

Volume limits

This volume is measured as the total additional volume added by the roof alteration, calculated by comparing the external roof profile before and after the work. Previous roof extensions (by you or a previous owner) count against the allowance. Roof windows (Velux-type) do not count towards the volume limit, but dormers do.

How to measure roof volume

Measuring roof volume correctly is critical and one of the most common mistakes homeowners and even some designers make. The volume is the external envelope of the addition measured from the outer surfaces -- not the internal habitable space. A rear dormer on a typical London Victorian terrace is usually 25–35 cubic metres, which is within the 40 m³ limit for terraced houses, but leaves little or no headroom for a side dormer as well.

We calculate roof volumes precisely as part of every loft conversion project. An error of even a few cubic metres can push a project outside PD and into a full planning application.

Other Class B conditions

Mansard loft conversions

Mansard roof extensions always require planning permission. A mansard alters the entire roof profile, adding a new storey with a distinctive angled-wall roof form. This is not a "roof addition" within the meaning of Class B -- it is effectively rebuilding the roof to create a new floor, which falls outside PD.

Class E: outbuildings and garden structures

Class E covers buildings, enclosures, swimming pools, and other structures within the curtilage of a house that are incidental to the enjoyment of the dwellinghouse. This includes garden offices, studios, summer houses, gyms, and outbuildings.

Key limits

A common question is whether a garden office with plumbing (a WC and kitchenette) loses its "incidental" status. HMRC and planning case law suggest that as long as the building is used by the occupants of the house (not rented out or used as a separate dwelling), the inclusion of basic amenities does not change its incidental nature. However, sleeping accommodation, separate utility meters, and a separate entrance from the street could indicate a change of use.

Conservation areas and PD restrictions

London has over 1,000 conservation areas. If your property is in one, your PD rights are reduced. Specifically, in a conservation area (classified as Article 2(3) land under the GPDO):

However, rear extensions under Class A are still permitted within the standard limits (including the Prior Approval route for larger extensions). And rear dormers are still permitted provided they are not visible from the highway. Many London terraced houses face a rear garden backed by another row of houses, meaning the rear dormer is only visible from neighbouring gardens, not from any public highway. In these cases, PD applies even in a conservation area.

Check your specific conservation area appraisal document on your borough's website. Some conservation area management plans specifically state which PD classes are restricted, and some boroughs have additional Article 4 Directions layered on top of the standard conservation area restrictions.

Article 4 Directions: when PD is removed entirely

An Article 4 Direction is a legal order made by a borough council that removes specified PD rights from a particular area. The name comes from Article 4 of the GPDO, which grants councils this power.

Article 4 Directions are common across London, particularly in conservation areas. They can remove any PD class -- or just specific ones. For example, an Article 4 Direction might remove the PD right to change windows and doors (forcing a planning application for replacement windows), while leaving the PD right to build a rear extension intact.

London boroughs with extensive Article 4 coverage

We check Article 4 status as part of every project. It is one of the first things we verify when assessing what permissions you need for your property. Get a free quote and we will confirm your PD status.

Flats and maisonettes: no PD rights

This is one of the most important points in this guide, and one that many London residents are unaware of: flats and maisonettes have no Permitted Development rights under Part 1 of the GPDO.

This means that if you live in a flat -- whether it is a purpose-built flat, a converted flat in a Victorian house, or a maisonette -- you need planning permission for any external alteration, however minor. This includes:

Internal alterations to flats do not need planning permission (unless the building is listed), but they may need building regulations approval and will typically require freeholder consent under your lease terms.

If you live in a flat and want to extend or alter the building, you need a full planning application. Our planning drawing packages cover flat applications at the same fixed fees as house applications.

How to measure roof volume for PD compliance

Accurate volume measurement is essential for any loft conversion that relies on PD rights. Getting it wrong -- even by a small margin -- means your development is unlawful.

Step-by-step method

  1. Survey the existing roof externally. Measure the roof slopes, ridge height, eaves height, and all relevant dimensions from the outside of the building.
  2. Model the existing roof volume as a 3D shape. For a simple pitched roof, this is a triangular prism. For hipped roofs, the geometry is more complex.
  3. Model the proposed roof including the dormer extension. Calculate the new external volume.
  4. Subtract the existing from the proposed. The difference is the additional volume added by your project.
  5. Include any previous roof additions. If a previous owner added a dormer or roof extension, its volume counts against your PD allowance.

The measurement is of the external envelope, not the internal floor area or habitable space. Wall thickness, insulation, and plasterboard all reduce the internal space relative to the external volume. A dormer that adds 35 m³ externally might only provide 28–30 m³ of usable internal space.

Professional measurement by an experienced architectural technologist is essential. At Architectural Drawings London, we provide precise volume calculations as part of every loft conversion project, along with a clear assessment of whether your project falls within PD or requires planning permission.

When are PD rights removed?

Your PD rights can be removed or restricted in several situations. Here is a comprehensive list of the circumstances where you may lose some or all PD rights in London:

  1. Article 4 Direction -- the council has made a legal order removing specific PD classes from your area
  2. Conservation area -- automatic restrictions on side extensions, highway-facing dormers, cladding, and large outbuildings
  3. Listed building -- PD rights apply to the curtilage (garden), but any work to the building itself requires Listed Building Consent
  4. Planning conditions -- when planning permission was originally granted for your house (or a previous extension), conditions may have been attached that specifically removed PD rights
  5. Flat or maisonette -- no Part 1 PD rights at all
  6. Previous PD use exhausted -- you (or a previous owner) have already used the full PD allowance (e.g. 50% garden coverage, 40/50 m³ roof volume)
  7. AONB, National Park, or World Heritage Site -- additional restrictions similar to conservation areas (rare in London, but parts of some outer boroughs border the Green Belt)
  8. The house has been subdivided -- if the house has been converted into flats, PD rights under Part 1 are lost
If you are unsure whether you have PD rights, the safest approach is to apply for a Lawful Development Certificate (LDC). This costs £129 and gives you a formal legal document from the council confirming that your proposed development is lawful. It is conclusive proof -- invaluable when you come to sell the property. We prepare LDC applications as part of our standard service.

Lawful Development Certificates: why you should always get one

Even when your project clearly falls within PD limits, we strongly recommend applying for a Lawful Development Certificate (LDC). Here is why:

The application costs £129 (proposed LDC) and is determined within 8 weeks. There is no neighbour consultation. The council simply checks your drawings against the GPDO conditions and confirms whether the development is lawful.

Get a free quote →

Frequently asked questions

What are Permitted Development rights in London?

Permitted Development (PD) rights are automatic planning permissions granted by the GPDO. They allow homeowners to carry out certain building work -- such as single-storey rear extensions, loft conversions, and outbuildings -- without applying for planning permission, provided the work meets specific size limits and conditions. In London, PD rights are more restricted than elsewhere in England due to conservation areas and Article 4 Directions. See our planning drawings service.

Can I build a rear extension under Permitted Development in London?

Yes. Under Class A, you can build a single-storey rear extension up to 6 metres deep (semi-detached or terraced) or up to 8 metres deep (detached, via Prior Approval). The maximum height is 4 metres, eaves height must not exceed 3 metres, and the extension must not cover more than 50% of the garden. These rights do not apply to flats, listed buildings, or properties where Article 4 Directions remove Class A. See our kitchen extension cost guide.

Do I have Permitted Development rights in a conservation area?

You have reduced PD rights in a conservation area. Rear extensions under Class A are still permitted within the standard limits, but you lose PD rights for side extensions, cladding, highway-facing dormers, satellite dishes on front or side elevations, and outbuildings over 10 sqm. Always check whether an Article 4 Direction further restricts PD in your specific conservation area. Read our full planning permission guide.

What is the Larger Home Extension scheme and does it still apply in 2026?

The Larger Home Extension scheme allows single-storey rear extensions of up to 8 metres (detached) or 6 metres (semi-detached/terraced) under a Prior Approval process. The council notifies neighbours and assesses the impact on amenity. This scheme was made permanent in 2019 and remains in effect in 2026. The council fee for a Prior Approval application is £120. View our drawing fees.

Do flats have Permitted Development rights in London?

No. Flats and maisonettes have no PD rights for extensions or external alterations under Part 1 of the GPDO. Any external work to a flat requires a full planning application. Internal alterations do not need planning permission (unless the building is listed), but may need building regulations approval and freeholder consent. Get a free quote for your flat project.

Last updated: April 2026