Insights

Do I Need Planning Permission For An Extension?

19 March 2026

If you’re investing in your home, one of the first and most important questions is: “do I need planning permission for an extension?” The answer depends on the size, location, and whether your property has restrictions such as listed status or conservation designation. So, what’s the answer?

You do not always need planning permission for an extension. Many extensions fall under Permitted Development (PD) rights, provided that they meet strict size, height, boundary, and design limits set out in The Town and Country Planning (General Permitted Development) Order 2015. Listed buildings and flats always require permission.

In this guide, we’ll explain the Permitted Development rules so that you can understand exactly how this will affect your project, whether you’ll need planning permission, and how to get it if it’s required.

Jump to section:

What Are Permitted Development Rights?
What Size Extension Can I Build Without Planning Permission?
When You Do Need Planning Permission
Listed Buildings & Heritage Properties
Building Regulations – Always Required
What Are The Risks of Building Without The Right Permission?
House Extensions in Sheffield
Official Sources & Government References

Internal view of a nearly completed house extension

What Are Permitted Development Rights?

Permitted Development is a legal provision allowing certain home improvements without a planning application – so long as strict conditions are met. These rights are set out in Schedule 2, Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015.

PD rights do not remove the need for:

Building Regulations approval (which is always required),
Party Wall agreements (if neighbour walls are affected),
Listed Building Consent (for heritage properties).

PD rights may also be restricted or removed by local authorities via Article 4 Directions.

What Size Extension Can I Build Without Planning Permission?

One of the most common questions is “what size extension can I build without planning permission?” Here’s how the rules break down under permitted development, with official guidance:

Single-Storey Rear Extensions

Single-Storey PD rights dictate:

A single-storey extension must not extend beyond the rear wall of the original house by more than:
- 3 metres (terraced or semi-detached),
- 4 metres (detached).
The maximum height must not exceed 4 metres
If the extension is within 2 metres of a boundary, the eaves height cannot exceed 3 metres.
The extension must not exceed more than 50% of the total land around the house.
It must not be forward of the principal elevation or visible from the front.

If you want to build larger than these sizes but still under PD rights, you can apply for prior approval, which typically follows:

Up to 6 metres (terraced or semi-detached), or
Up to 8 metres (detached).

Side Extensions

Under PD rights, a single-storey side extension must:

Be single-storey only,
Be no more than 4 metres high,
Be no wider than half the width of the original house,
Not be forward of the principal elevation or facing a highway.

Two-storey side extensions are not covered by PD and will generally require planning permission.

Two-Storey Rear Extensions

Some two-storey rear extensions can qualify under PD, as long as:

They do not extend more than 3 metres beyond the rear wall of the original house,
They are at least 7 metres away from the rear boundary,
The roof pitch matches the existing home,
Upper-floor side windows are obscure-glazed and non-opening unless 1.7m above floor level,
The overall height does not exceed the existing roof height.

If any of these conditions are not met, full planning permission will be required.

Scaffolding and building blocks of an early-build house extension

When You Do Need Planning Permission

Even if an extension appears to fit within permitted development limits, planning permission could still be required if:

You are in a conservation area, National Park, AONB, or World Heritage Site
Your property is listed,
Your permitted development rights have been removed by a planning condition.
You will also need planning permission if your extension will:
- Exceed the PD size limits above,
- Project forward of the principal elevation,
- Result in more than 50% coverage of the land around the original house.

In these cases, a formal planning application must be submitted to your local planning authority.

Listed Buildings & Heritage Properties

If your home is a listed building, PD rights generally do not apply. Any exterior alteration or extension affecting the character of the building will require Listed Building Consent under the Planning (Listed Buildings and Conservation Areas) Act 1990, and often full planning permission as well.

In these cases, early planning consultation is essential to avoid enforcement action, so working with an experienced architect or planning consultant is a must.

See our Grade II Listed Building Full Refurbishment & Extension Case Study

Internal view of a mid-build house extension

Building Regulations – Always Required

Whether or not planning permission is needed, Building Regulations approval is mandatory for any structural extension under The Building Regulations 2010. This ensures:

Structural safety,
Fire protection,
Insulation & ventilation compliance,
Safe drainage and energy performance.

Planning permission and building control are separate processes.

What Are The Risks of Building Without The Right Permission?

Building without the correct permissions, even when you think PD applies, can result in:

Enforcement notices (requiring demolition or alteration),
Delays or complications on resale,
Retrospective application fees and additional work.

For example, an unauthorised two-storey extension built without planning permission can lead to enforcement action and costly revisions.

External view of a completed building extension

House Extensions in Sheffield

If you’re considering extending your home in Sheffield, understanding planning permission early helps you to avoid delays, maximise space, and safeguard your investment.

Whether you’re planning a modest single-storey kitchen extension or a larger two-storey redesign, our team can help you through the process with expert recommendations.

Get in touch with Jenkinson Construction Group’s experts and get clear advice that is tailored to your property.