Do You Need Planning Permission for an Extension?

admin42315
Mar 24
4 min read

Permitted Development Rights let you build extensions without planning permission, subject to size and location restrictions.
Extensions can't cover more than half your garden, must match existing materials, and can’t exceed certain height and length limits.
Listed buildings, flats, and homes in conservation areas usually require planning permission.
Always get a Lawful Development Certificate to prove compliance.
Building Regulations and party wall agreements still apply—always check with your local council first!

More than 40% of UK homeowners plan to extend or significantly remodel their homes in the next three years, yet many are unsure about whether their projects require planning permission. Building an extension can dramatically increase your home's value, enhance living spaces, and improve your lifestyle—but navigating the planning regulations can be a daunting task. Trust me, you're not alone if you've ever felt confused!

To help clarify the ins and outs, this guide will walk you through exactly when planning permission for an extension is necessary, when it's not, and what "permitted development rights" actually mean in practice.

When You Do NOT Need Planning Permission

Great news first! You don't need planning permission for an extension if your project falls within your property's permitted development rights. Permitted development rights allow homeowners to extend their properties without formal approval, provided certain rules are followed. But there are limits, of course.

Here's a clear snapshot of these permitted development limits:

Single-Storey Extensions (Under Permitted Development)

You can build without planning permission if:

The extension doesn't cover more than half the total area of land around the original property (including other buildings).
It’s not positioned in front of your home or facing a public highway.
It doesn't rise above the highest part of your roof.
The materials used match those of your existing home.
It doesn't exceed 4 metres in height.
It extends no more than:
- 6 metres beyond the rear wall (semi-detached or terraced homes).
- 8 metres beyond the rear wall (detached homes).

Side Extensions (Without Formal Permission)

For side extensions specifically, you won't need permission if your extension:

Is single-storey only.
Doesn't exceed 4 metres in height.
Isn't wider than half of your home's original width.
Isn't front-facing or facing the highway.

When You DO Need Planning Permission for an Extension

Not all extensions qualify for permitted development—so here’s when planning permission becomes essential:

Your extension covers over half of your home's original garden or outdoor space.
It's higher than your property's original roof.
It uses significantly different building materials from your current home.
You're building balconies, raised platforms, or verandas—those always trigger permission!

Additionally, for two-storey extensions, you’ll need approval if:

It extends more than 3 metres beyond the original home's rear wall.
It's within 7 metres of your property's rear boundary.
The side-facing windows are not obscure-glazed, or they're able to open below 1.7 metres from the room’s floor.
The roof pitch doesn't match your existing home.

Secondary Keywords: Listed Buildings, Flats, and Conservation Areas

Certain special circumstances always trigger the need for planning approval. For example, if your home is in a designated area—such as a conservation area or an area of outstanding natural beauty—your permitted development rights might be restricted. Likewise, listed buildings and properties like flats and maisonettes have minimal permitted development rights, meaning you'll usually need explicit planning permission.

Additional Considerations Before You Start Your Extension

Beyond planning permission, there are other important factors to keep in mind:

Lawful Development Certificates (LDC)

Even if you're certain your extension is within permitted development, I strongly recommend getting a Lawful Development Certificate from your local council. It’s proof that your project complied fully with regulations at the time of construction, providing peace of mind, especially if you later decide to sell your home. Believe me, this small step can save you countless headaches in the future!

Building Regulations Approval

Planning permission isn’t your only obligation. All extensions must meet UK Building Regulations, which cover important safety and structural standards such as insulation, ventilation, and fire safety. Building regulations are separate from planning permissions—so always ensure your project is compliant on both fronts.

Party Wall Agreements and Neighbour Consultations

Considering your neighbours’ rights and interests is crucial. For instance, if you're building close to or directly on a shared boundary, you'll need a party wall agreement. This ensures both your interests and your neighbours' are protected. Also, for larger rear extensions (between 4-8 metres), you'll need to follow the "neighbour consultation scheme," giving neighbours the opportunity to raise valid concerns.

How to Check if Your Project Needs Permission (Actionable Steps)

Assess your property's permitted development rights:Check your property's history—previous extensions may reduce your current allowance.
Speak to your local planning authority:Each local authority may interpret permitted development differently, so a quick call can clear things up.
Apply for a Lawful Development Certificate (LDC):Even when you're confident in your permitted development rights, an LDC is invaluable if you sell.
Engage with a qualified architect or planning professional:Professionals can quickly assess and handle your planning situation—reducing risk and stress.

Summing Up: Your Next Steps

Understanding planning permissions and permitted development might initially seem overwhelming, but armed with the right information, it's straightforward. Whether you're dreaming of a spacious new kitchen, a sunny morning room, or a quiet home office, knowing exactly when planning permission for an extension is required will save you time, money, and frustration.

As a trusted contractor, we’ve guided many homeowners through this process. When in doubt, always reach out to a professional to discuss your unique situation—we’re here to help!