Most single-storey rear extensions in England do not require planning permission. They fall under Permitted Development (PD) rights — a pre-approved consent that lets homeowners build within defined dimensional limits without a formal application. The moment an extension exceeds those limits, or the property falls into an excluded category, you need either Prior Approval or a full planning application.
This article covers PD size limits, the extended Prior Approval route, when full permission is required, Lawful Development Certificates, and the separate party wall process — all figures are for England in 2026.
Scotland, Wales and Northern Ireland have separate planning regimes and are not covered here.
Permitted Development Rights: What They Are and Where They Come From
Permitted Development rights for house extensions derive from Schedule 2, Part 1, Class A of the Town and Country Planning (General Permitted Development) (England) Order 2015 (GPDO). They are attached to the property, not the owner, and can be removed by an Article 4 Direction (a local authority instruction) or by a planning condition on the original consent — common on new-build estates. Always check your title register or call the local planning authority before assuming PD applies.
Where PD rights do not apply
- Flats and maisonettes — no Class A PD rights; any extension needs full permission
- Listed buildings — PD suspended; Listed Building Consent also required
- National Parks, AONB, and World Heritage Sites — reduced PD; side and two-storey extensions excluded
- Conservation Areas — front extensions excluded; check with the council for rear/side
- Article 4 Direction areas — local authority has removed PD (common in some London boroughs)
- Planning condition on original consent — check the decision notice for your property
Single-Storey Rear Extension: PD Size Limits
For the majority of houses in England not caught by the exclusions above, a single-storey rear extension is PD if it satisfies all of the following simultaneously:
| Parameter | Detached house | Semi-detached / Terraced |
|---|---|---|
| Maximum depth from original rear wall | 4 m | 3 m |
| Maximum eaves height | 4 m | 4 m |
| Maximum overall height | 4 m | 4 m |
| Eaves height within 2 m of boundary | 3 m max | 3 m max |
| Maximum garden coverage (all outbuildings combined) | 50% | 50% |
Depth is measured from the original rear wall of the dwelling — meaning the wall as it existed when the house was built, or as it stood on 1 July 1948 for older properties. If a previous owner already extended 2 m into the garden, you only have 1 m of PD depth left on a semi-detached, not 3 m. The GPDO measures cumulative extensions, not just the current proposal.
Additional conditions that must all be met:
- The extension must not extend beyond the front wall (principal elevation) of the house at any point
- It must not include a raised platform, balcony, or veranda — a standard ground-level patio is fine; a decked platform over 300 mm above ground is not PD
- Materials must be of similar appearance to the existing house — matching brick, render, or roofing material
- Roof lights on extension roofs must not project more than 150 mm above the plane of the roof slope
Two-Storey and Upper-Floor Extensions
Two-storey rear extensions are permitted development under stricter limits:
- Maximum depth: 3 m (all house types)
- Must be at least 7 m from the rear boundary — measured horizontally to the nearest point of the extension
- The roof pitch must match the main house as far as practicable
- No windows in the side elevation of a two-storey extension unless they are obscure-glazed and non-opening below 1.7 m from finished floor level
Side extensions are PD only if single storey, with a maximum width of 50% of the original house width and a maximum height of 4 m. In designated areas (National Parks, AONB, Conservation Areas), side extensions — even single storey — generally require full planning permission.
The Larger Home Extension Scheme (Prior Approval)
Since 2019, the Neighbour Consultation Scheme — officially the Larger Home Extension route under Class A — has allowed single-storey rear extensions almost double the standard PD limits, subject to a formal Prior Approval process:
| House type | Maximum depth under Larger Home Extension |
|---|---|
| Detached house | 8 m |
| Semi-detached house | 6 m |
| Terraced house | 6 m |
Height limits remain the same as standard PD (4 m overall, 3 m eaves within 2 m of boundary).
How the Prior Approval process works
Submit a Prior Approval application via the Planning Portal (fee: £258). The council writes to immediately adjoining neighbours, who have 21 days to comment. If no objections arrive — or if the council considers any objections do not demonstrate unacceptable amenity impact — Prior Approval is granted. Silence from the council after 42 days from submission is automatically treated as approved. The council can only assess neighbour amenity impact; it cannot refuse on design or appearance grounds. If refused, you can appeal to the Planning Inspectorate or fall back to the standard PD limits at no further cost.
When You Need Full Planning Permission
A full householder planning application is required when any of the following apply:
- Extension exceeds PD or Larger Home Extension size limits
- Property is a flat, maisonette, or listed building
- Conservation Area and the extension is to the front or is two-storey side
- Article 4 Direction in force, or PD removed by planning condition
- Extension includes a balcony, raised platform, or veranda
- Extension would take total outbuilding coverage over 50% of the curtilage
Householder application: costs and timescales
| Item | Detail |
|---|---|
| Application fee (England, from April 2024) | £258 |
| Target decision period | 8 weeks |
| Complex or contentious cases | Up to 13 weeks |
| Planning permission validity | 3 years from date of decision |
| Appeal deadline if refused | 6 months from decision date |
Submit via the Planning Portal (planningportal.co.uk). Required documents typically include a site location plan at 1:1250, block plan at 1:500, and existing/proposed floor plans and elevations at 1:50 or 1:100.
Lawful Development Certificates
Even when an extension is clearly permitted development and needs no planning application, it is strongly recommended to apply for a Lawful Development Certificate (LDC) before or shortly after the work is completed.
An LDC is a formal legal document issued by the council confirming that the works were lawful at the time they were carried out. It does not grant permission — it records that no permission was needed.
- Fee in England: £129 (half the householder application fee)
- Determination period: 8 weeks (same as full planning)
- Apply via: Planning Portal, as an application for a Certificate of Lawful Proposed Use or Development (CLPUD) before work, or Certificate of Lawful Existing Use or Development (CLEUD) after
Without an LDC you are relying on the PD argument holding up if challenged on sale or remortgage. Most conveyancing solicitors will flag the absence of one on an extended property, so it is worth obtaining before you sell.
Party Wall: Separate from Planning, Often Concurrent
Planning permission and the Party Wall etc. Act 1996 are entirely separate legal frameworks — you can need both, one, or neither. They run in parallel.
The Party Wall Act catches most rear extensions via three routes: Section 6 (excavating within 3 m of a neighbour’s foundations — nearly every extension); Section 1 (building on or at the boundary line); and Section 2 (work on a shared party wall, e.g., removing a chimney breast).
Party wall procedure in brief
Serve written notice on affected adjoining owners at least 2 months before work begins (party wall works) or 1 month before (adjacent excavation only). Neighbours have 14 days to respond. Written consent means no surveyor is needed. If they dissent, fail to respond, or do not reply within 14 days, a dispute is deemed to have arisen and both parties appoint surveyors to agree a Party Wall Award. The building owner typically pays both surveyors’ fees: allow £700–£1,500 per owner in the South East. The whole process adds 1–3 months to the pre-construction programme and is the most common cause of delayed starts on otherwise straightforward extensions.
Quick-Reference Planning Route Table
| Extension type | Typical planning route | Key size limit | Fee |
|---|---|---|---|
| Single-storey rear, within standard limits | Permitted Development — no application | 4 m depth (detached); 3 m (semi/terrace) | £0 (LDC recommended at £129) |
| Single-storey rear, 4–8 m / 3–6 m depth | Prior Approval (Larger Home Extension) | 8 m (detached); 6 m (semi/terrace) | £258 |
| Two-storey rear, within PD limits | Permitted Development — no application | 3 m depth; 7 m from rear boundary | £0 (LDC recommended at £129) |
| Side extension (single storey, within limits) | Permitted Development — no application | 50% of original house width; 4 m high | £0 |
| Any extension on a flat or maisonette | Full planning permission required | No PD rights — any size | £258 |
| Extension on a listed building | Full planning permission + Listed Building Consent | Any size | £258 + £0 (LBC has no fee) |
| Extension exceeding PD/Prior Approval limits | Full planning permission required | Any size | £258 |
Frequently Asked Questions
Do I need Building Regulations approval even if my extension is permitted development?
Yes, always. Planning and Building Regulations are completely separate. Virtually all structural extensions require Building Regulations approval — either via a Full Plans application to building control before work starts, or a Building Notice. PD status has no bearing on this.
Can my neighbour block my extension?
Not through the planning system for standard PD — there is no public consultation. Under the Larger Home Extension Prior Approval route, neighbours can object and the council may refuse on amenity grounds. Under the Party Wall Act, neighbours can trigger a surveyor process that delays the start by 1–3 months, but cannot ultimately veto lawful works; the Party Wall Award sets conditions, not a right of refusal.
How long is planning permission valid?
Three years from the date of the decision notice. You must start a material operation within that period; completion afterwards is fine.
I built an extension without checking — what now?
Establish whether the extension was PD at the time it was built. If it was, apply for a retrospective LDC (CLEUD — Certificate of Lawful Existing Use or Development). If it genuinely required planning permission, apply retrospectively — councils can and do grant it. The risk of doing nothing is an enforcement notice: councils have 4 years from the date of the breach to take enforcement action on residential extensions. Enforcement notices can require demolition, so regularise early.
