Is My Extension Permitted Development?

Dreaming of a spacious new kitchen-diner or a light-filled family room? For many homeowners in England, the biggest hurdle isn’t the building work—it’s the perceived nightmare of navigating the planning permission system. But what if you could bypass the process altogether?

Welcome to the world of Permitted Development Rights. This isn't a loophole; it's a government-sanctioned fast track for common home improvement projects, including single-storey rear extensions. Get it right, and you can save yourself months of waiting and uncertainty. Get it wrong, and you could face a costly enforcement notice from your local council.

This guide will demystify the core rules, clarify the common points of confusion, and introduce the powerful but often misunderstood "Prior Approval" route for even larger extensions.

What are Permitted Development (PD) Rights?

Think of PD rights as a standing grant of planning permission from central government. They are set out in law, primarily in The Town and Country Planning (General Permitted Development) (England) Order 2015. If your project fits perfectly within the specified limits, you don’t need to file a full planning application because the permission has, in effect, already been granted.

These rights only apply to houses. Flats, maisonettes, or other types of buildings do not have the same permitted development rights.

The Core Rules: How Far Can You Extend?

For a standard single-storey rear extension, the crucial dimension is how far you project from the ‘rear elevation’ of the original house (the house as it stood on 1 July 1948 or when it was first built).

• For a terraced or semi-detached house: You can extend up to 3 metres.

• For a detached house: You can extend up to 4 metres.

But this is just the starting point. To qualify, your extension must also meet several other critical criteria:

• Height: It can't be higher than the highest part of your existing roof. The maximum height for a single-storey rear extension is 4 metres.

• Eaves Height: If the extension comes within 2 metres of a boundary, the height at the eaves (where the wall meets the roof) cannot exceed 3 metres.

• Land Coverage: The extension, along with all other sheds and outbuildings, must not cover more than 50% of the total area of land around the original house (your garden/curtilage).

• Location: The extension must not be forward of the ‘principal elevation’ (usually the front of your house) or a side elevation that fronts a highway.

• Materials: The materials used in any exterior work must be of a similar appearance to those on the exterior of the existing house.

• Designated Land: If your property is in a Conservation Area, an Area of Outstanding Natural Beauty (AONB), a National Park, the Broads, or a World Heritage Site, your PD rights will be more restricted. These larger extensions are often not permitted, and you should always check with your local planning authority.

The Lesser-Known Tactic: The 'Larger Home Extension' Scheme

What if you want to go bigger than 3 or 4 metres? There is a popular route that allows for this, but it comes with an extra step. Under the 'Larger Home Extension' scheme, you can build a single-storey rear extension of up to:

• 6 metres for a terraced or semi-detached house.

• 8 metres for a detached house.

However, this is not a typical Permitted Development right. It is subject to a process called Prior Approval.

How Prior Approval Works:

1. Notification: You must notify your local council before you start work, providing them with plans and details.

2. Consultation: The council will then consult your immediate neighbours.

3. Decision: If your neighbours do not object, and the council finds the project meets the rules and is unlikely to have an unacceptable impact on neighbours' amenity, they will issue a notice stating that Prior Approval is not required, and you can build. If a neighbour objects, the council must assess the impact on their light and privacy before making a decision.

This process is simpler, cheaper, and faster (typically a maximum of 42 days) than a full planning application, but it is not a rubber stamp. It is a critical step that must be completed before any work begins.

Common Pitfalls & Red Flags

• Measuring Height on Sloped Ground: This trips many people up. Height is always measured from the natural ground level immediately outside the extension. You cannot artificially lower the ground by digging out your garden to give yourself more height.

• What is the 'Principal Elevation'? For most houses, it’s the front elevation facing the main road. It's the face that determines the character of the property. You cannot use PD to build an extension in front of this.

• Wraparound Extensions: A 'wraparound' extension (one that extends to the rear and the side) is considered to be two separate extensions. The side element has its own set of rules and limitations, and together they may not fall under Permitted Development.

• Previous Extensions: PD rights apply to the "original house." If the property has already been extended by previous owners, you may have used up some or all of your allowance.

When to Seek Professional Help

Permitted Development rules are a legal minefield. If you have any doubt, especially if your property is on designated land, has been extended before, or your design is close to the limits, it is wise to seek professional advice.

For 100% certainty, you can apply for a Lawful Development Certificate (LDC) from your council. This isn't planning permission, but it is a legally binding confirmation that your proposed project is lawful and does not require it. It’s an invaluable document for your own peace of mind and for when you eventually sell the property.