Most single-storey rear extensions in England do not require planning permission — they qualify as Permitted Development (PD). A single-storey rear extension up to 3m deep on an attached house (or 4m on a detached house) can proceed without any planning application. Extensions up to 6m (attached) or 8m (detached) are possible under the Neighbour Consultation Scheme with prior approval. Planning permission is required for: properties in conservation areas, listed buildings, two-storey side extensions, wraparound extensions, and any extension that exceeds PD size limits. Building Regulations approval is always required, regardless of whether planning permission is needed.
Permitted Development Rules by Extension Type
Permitted Development (PD) rights allow homeowners to carry out certain types of building work without applying for planning permission. The rules differ by extension type. The table below summarises the key rules for each common extension type.
- Maximum depth: 3m for attached houses, 4m for detached houses (standard PD)
- Maximum depth: 6m for attached, 8m for detached under the Neighbour Consultation Scheme
- Maximum height: 4m
- Must not extend beyond the principal elevation or a side elevation fronting a highway
The most common extension type. Most single-storey rear extensions qualify as Permitted Development without any application.
- Maximum depth: 3m from the original rear wall
- Maximum height: no higher than the existing roof ridge
- Eaves height must not exceed the existing eaves height
- Must be at least 7m from the rear boundary
- No balconies, verandas, or raised platforms
- Roof pitch must match the existing house as far as practicable
Subject to more restrictions than single-storey. The 7m rear boundary rule catches many properties in London with smaller gardens.
- Maximum width: half the width of the original house
- Maximum height: 4m
- Must not extend beyond the principal elevation
- Cannot be used to create a separate dwelling
Side extensions on corner plots or properties fronting a highway often require planning permission, as they may affect the street scene.
- Combines a side and rear extension in an L-shape
- Almost always requires planning permission
- The side element typically exceeds PD limits or affects the principal elevation
Wraparound extensions are one of the most popular extension types in London but almost universally require a planning application.
- Two-storey side extensions always require planning permission
- They are not permitted under PD rights
Any side extension that extends to two storeys falls outside Permitted Development and requires a full planning application.
- Porch: maximum ground floor area 3m², maximum height 3m
- Must be at least 2m from the boundary of the property with a highway
- Front extensions beyond a porch almost always require planning permission
Porches have their own specific PD rules. Any other extension to the front of a property requires planning permission.
Permitted Development Size Limits at a Glance
The following table summarises the key size limits for house extensions under Permitted Development rights in England (as of 2025). These limits apply to the original house — the house as it was first built, or as it stood on 1 July 1948 if built before that date.
| Rule | Limit | Application Required? |
|---|---|---|
| Single-storey rear — attached house (standard PD) | 3m depth | No application needed |
| Single-storey rear — detached house (standard PD) | 4m depth | No application needed |
| Single-storey rear — attached house (Neighbour Consultation Scheme) | Up to 6m depth | Prior approval required |
| Single-storey rear — detached house (Neighbour Consultation Scheme) | Up to 8m depth | Prior approval required |
| Double-storey rear extension | 3m depth, 7m from rear boundary | No application needed if all conditions met |
| Single-storey side extension | Half the width of original house | No application needed if all conditions met |
| Maximum height (single-storey) | 4m | Applies to all single-storey PD extensions |
| Maximum height (double-storey) | No higher than existing ridge | Eaves must not exceed existing eaves height |
* These limits apply to houses in England only, and assume PD rights have not been removed by an Article 4 Direction or planning condition.
When Planning Permission Is Required
Eight scenarios reliably trigger a planning permission requirement, regardless of the size of the proposed extension. If any of these apply to your property, a planning application is needed before work begins.
In a conservation area, side extensions and any extension that would be visible from a highway require planning permission. Rear extensions may still qualify as PD.
Listed Building Consent is required for any works that affect the character of a listed building, in addition to planning permission. This applies even to internal alterations.
Local authorities can remove Permitted Development rights through an Article 4 Direction. This is common in conservation areas and some estates. Check with your local planning authority.
If the proposed extension exceeds any of the size limits described above, a full planning application is required.
Permitted Development rights do not apply to flats, maisonettes, or converted houses. All extensions to these properties require planning permission.
Any extension intended to create a self-contained dwelling (with its own entrance, kitchen, and bathroom) requires planning permission for a change of use.
Corner plots often have additional restrictions. Extensions on the side elevation fronting a highway require planning permission.
PD rights apply to the original house, not the current house. If previous owners have already extended, the remaining PD allowance may be zero.
Article 4 Directions: When PD Rights Are Removed
An Article 4 Direction is a legal instrument that allows a local planning authority to withdraw Permitted Development rights in a specific area. Where an Article 4 Direction applies, works that would normally be Permitted Development require a planning application instead.
Article 4 Directions are most commonly applied in conservation areas, Areas of Outstanding Natural Beauty, and certain residential estates where the local authority wants to protect the character of the area. They are also sometimes applied to specific types of development — for example, removing PD rights for the conversion of houses to flats.
Checking whether an Article 4 Direction applies to your property is straightforward — contact your local planning authority or search the planning portal. TCM checks this as a matter of course for all extension projects before providing a quotation.
Important: Carrying out works that require planning permission without obtaining it is a breach of planning control. The local authority can issue an Enforcement Notice requiring the works to be reversed at the owner's expense. There is no time limit for enforcement action on works that required but did not obtain planning permission.
Conservation Areas & Listed Buildings
Properties in conservation areas have reduced Permitted Development rights. In a conservation area, the following works require planning permission even if they would normally be PD: any extension that is visible from a highway, side extensions, and cladding the exterior of the house in stone, artificial stone, pebble dash, render, timber, plastic, or tiles.
Rear extensions in conservation areas may still qualify as PD, provided they are not visible from a highway and meet all other PD conditions. However, the local planning authority will scrutinise the design more closely, and the materials used must be sympathetic to the character of the area.
Listed buildings require both planning permission and Listed Building Consent for any works that affect their character — including internal alterations. The definition of "affecting the character" is broad, and even replacing windows or adding insulation can require consent. TCM always advises clients with listed buildings to seek pre-application advice from the local planning authority before committing to a design.
London Borough-Specific Rules
London has a higher concentration of conservation areas and Article 4 Directions than most of England. The boroughs TCM works in most frequently each have their own specific planning context.
Article 4 Directions apply in several conservation areas including Cranbrook, Valentines, and parts of Barkingside. Check the Redbridge planning portal before assuming PD applies.
Extensive conservation areas across Barnet, East Barnet, Totteridge, and Hampstead Garden Suburb. The Hampstead Garden Suburb area has very strict controls — most extensions require planning permission.
Conservation areas in Edmonton, Enfield Town, and Forty Hill. Article 4 Directions apply in several residential areas. PD rights are generally intact in most of Enfield.
Conservation areas in Highams Park, Walthamstow Village, and Epping Forest fringes. The council has been active in applying Article 4 Directions in recent years.
Relatively few conservation area restrictions in Borehamwood itself. Rural and village areas in Hertsmere have more controls. PD rights generally apply in most residential areas.
Conservation areas in Hoddesdon, Waltham Cross, and Cheshunt. Green Belt restrictions apply to properties on the eastern fringes. Always check before assuming PD applies.
The Neighbour Consultation Scheme (Larger Home Extensions)
The Neighbour Consultation Scheme (also called the Prior Approval process for larger home extensions) allows homeowners to build single-storey rear extensions larger than the standard PD limits — up to 6m deep on an attached house and up to 8m deep on a detached house — without a full planning application.
To use the scheme, you must notify the local planning authority before work begins. The authority then notifies adjoining neighbours, who have 21 days to object. If no objections are received, or if the authority decides the impact on neighbours is acceptable, Prior Approval is granted and work can proceed.
- A written description of the proposed works
- A plan showing the site and the proposed extension
- The addresses of any adjoining properties
- The impact on the amenity of adjoining properties
- The impact on the character of the area
- Whether the extension meets all PD conditions
The scheme does not apply in conservation areas, Areas of Outstanding Natural Beauty, or where Article 4 Directions have removed PD rights. The decision period is 42 days from the date the authority receives the application.
Building Regulations: Always Required
Planning permission and Building Regulations are two entirely separate processes. Planning permission controls whether a building can be built and what it looks like. Building Regulations control how it is built — the structural, thermal, fire safety, and electrical standards it must meet.
Building Regulations approval is required for all house extensions, regardless of whether planning permission is needed. There are no exceptions. TCM submits a Full Plans application to the relevant local authority Building Control (or an Approved Inspector) at the start of every project, and all work is inspected at key stages.
Certificate of Lawful Development: Why You Need One
Even when an extension qualifies as Permitted Development and no planning application is required, obtaining a Certificate of Lawful Development (CLD) is strongly recommended. A CLD is a formal legal document from the local planning authority confirming that the proposed works are lawful.
Without a CLD, you are relying on your own interpretation of the PD rules. If your interpretation is wrong — or if the rules change — you may face enforcement action. More practically, solicitors acting for buyers in a property sale will ask for evidence that any extensions were lawfully built. An absence of a CLD can delay or derail a sale.
The application fee is £258 (half the cost of a householder planning application). The local authority has 8 weeks to determine the application. TCM prepares and submits CLD applications on behalf of clients as part of the project management service.
How to Apply for Planning Permission
When planning permission is required, the process follows a defined sequence. TCM manages the entire process on behalf of clients, from pre-application advice through to decision.
Most local authorities offer a paid pre-application advice service. For extensions in conservation areas or where the design is unconventional, this is worth the cost — it identifies potential issues before the formal application is submitted.
A householder planning application requires existing and proposed floor plans, elevations, and a site location plan. TCM's in-house design team prepares all drawings to the required standard.
Applications are submitted via the Planning Portal (planningportal.co.uk). The application fee for a householder application is £258. The authority has 8 weeks to determine the application.
The local authority notifies neighbours and consults statutory consultees (e.g., highways, ecology). Neighbours have 21 days to comment. Comments are a material consideration but not a veto.
The planning officer assesses the application against the Local Plan policies and national planning policy. Most householder applications are decided under delegated powers without going to committee.
Planning permissions often include conditions (e.g., materials to be approved, hours of construction). These must be formally discharged before or during construction.
TCM Building & Maintenance provides free planning advice for all extension projects across London and Hertfordshire. We'll assess your property, confirm whether planning permission is required, and advise on the fastest route to getting your project started.