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Do You Need Planning Permission for an Extension?
A clear guide to planning permission rules for home extensions in 2026. What you can build under permitted development, when you need to apply, and what Lancashire homeowners should know.
Most single-storey extensions in England can be built without planning permission under permitted development rights. The rules are specific and depend on the type of extension, its size, and where your property is located.
This guide explains the current rules so you can work out whether your project needs a planning application before you spend money on drawings.
What is permitted development?
Permitted development is a set of rights built into national planning law that allows homeowners to carry out certain building work without a formal planning application. Around 60 to 70 percent of UK home extensions are built this way.
If your extension stays within the permitted development limits, it is automatically legal. You do not need approval from your local council. You will still need building regulations approval, which is a separate process covering structural safety, drainage and energy efficiency.
Permitted development limits for rear extensions
These are the current size limits for single-storey rear extensions under permitted development in England.
Detached houses: Up to 4 metres deep under standard PD, or up to 8 metres under the Larger Home Extension scheme (subject to neighbour consultation).
Semi-detached and terraced houses: Up to 3 metres deep under standard PD, or up to 6 metres under the Larger Home Extension scheme.
In all cases, the maximum eaves height is 3 metres if within 2 metres of a boundary, and 4 metres in other positions. Materials must be similar to the existing house.
The Larger Home Extension scheme
If your extension is between the standard limit and the larger limit (for example, a 5-metre rear extension on a semi-detached house), you need to go through the Prior Approval process. This is not a full planning application. It is a simpler 21-day neighbour consultation managed by the local council.
If no objections are raised, the council confirms approval and you can proceed. If a neighbour objects, the council assesses the impact and may still approve the work or may require changes.
Two-storey extensions
Two-storey rear extensions are allowed under permitted development only if they project no more than 3 metres from the original rear wall, are no higher than the existing roof, sit at least 7 metres from the rear boundary, and use matching materials. Side-facing upper-floor windows must be obscure-glazed and non-opening below 1.7 metres.
In practice, most two-storey extensions exceed at least one of these limits and require full planning permission.
Side extensions
Single-storey side extensions are permitted under PD if they are no more than 4 metres high and no wider than half the width of the original house. All side extensions of more than one storey require planning permission.
The 50 percent rule
Across all extensions combined, you cannot build on more than 50 percent of the land surrounding the original house. Previous extensions, outbuildings and sheds all count toward this limit, even if they were built by a previous owner.
This is the rule that catches many homeowners in East Lancashire, particularly on terraced properties with smaller gardens.
When you always need planning permission
Permitted development rights do not apply in certain situations, regardless of the size of your extension.
Listed buildings. Any external work to a listed building requires both Listed Building Consent and full planning permission. This applies to all Grade I, II* and II listed properties.
Conservation areas. Properties in conservation areas have reduced permitted development rights. Side extensions, cladding changes and some roof alterations need permission. Several areas across the Ribble Valley and parts of Pendle fall within conservation areas, so always check before assuming PD applies.
Areas of Outstanding Natural Beauty and National Parks. Stricter rules apply in these designated areas. Parts of the Forest of Bowland AONB extend into the Ribble Valley and Pendle areas.
Flats and maisonettes. Permitted development rights for extensions apply to houses only, not flats.
Article 4 Directions. Some councils remove permitted development rights from specific streets or areas. Check with your local planning authority.
What does a planning application cost?
A standard householder planning application in England costs £258 in 2026. The determination period is typically 8 weeks, though in practice it can take 8 to 12 weeks.
If you want to confirm that your extension qualifies as permitted development, you can apply for a Lawful Development Certificate (LDC) for approximately £146. This provides legal confirmation that the work is permitted and is useful evidence when you come to sell the property.
Our recommendation
Whether or not your extension needs planning permission, always check with your local planning authority before starting work. A quick call or email to Burnley or Pendle Borough Council's planning team can confirm your rights and prevent costly problems later.
If you're unsure about the rules for your property, we can help. We assess permitted development as part of every extension project and advise on the best route before any work begins.
Planning an extension?
We handle the planning process for you.
Renex owner Caleb has spent 15 years helping homeowners improve their properties through extensions, renovations and landscaping projects across Lancashire. Book a home visit to discuss your ideas, explore what's possible and get straightforward advice on the best way to move your project forward. There's really nothing to lose.
