Planning permission for an extension – do you actually need it?

Adding an extension is a route many of us take to get the space we need in our homes. And it doesn't always have to be a large addition - increasing the floorplan by a metre or two will give you the chance to rejig and create a wonderful, workable space.

But, will you need planning permission for an extension? It's a common query and knowing the answer can help steer the outcome of your project. 

Do you need planning permission for an extension?

The good news is that you won't necessarily need planning permission to extend. A set of rules called Permitted Development (PD) rights mean you can extend without having to go down the official planning route. The rules are strict however, so it pays to know what they are. In this guide we explain what you can build without planning permission - it centres on areas like height, size and position of the extension, as well as where you live. 

We also look at when planning permission for an extension is needed, or when it could be the better route for your project.

Permitted Development rights for extensions

There is a definitive guide to Permitted Development rights contained in the Government's Permitted Development Rights for Householders: Technical Guidance. The detail does vary slightly in Scotland, Wales and Northern Ireland.

The guides are comprehensive, a bit technical and therefore a bit daunting, especially if you've not come across this information before.

So we appreciate you might want a more top-line guide, and that's where we come in. These are the answers to your big extension questions…

Do all properties have Permitted Development rights?

No, not all homes have Permitted Development rights. When it comes to planning permission for an extension there are some general caveats and restrictions that you should know.

• House already been extended?
  If the house has been extended before - by you or a previous homeowner - then it is highly unlikely that you can use Permitted Development rights again because an addition will push you over the size criteria. 
• Live in a listed building?
  If you live in a listed building or your home resides in a designated area, such as an area of outstanding natural beauty or in a conservation area, then you should speak to your local planning office about PD rights. These rights can be removed by a council under Article 4, which aims to maintain the character of an area, therefore restricting or revoking what can be built under PD rights. 
• Live in a flat?
  Then Permitted Development rights do not apply. The same goes for maisonettes. 

What size extension can I build without planning permission?

This depends on how big your plot is and what’s already on it. You can build an extension under Permitted Development rules as long as it doesn’t exceed 50% of the area of land your house sits on. That 50% excludes the area covered by the house itself, but does include any existing additions and outbuildings.

Here's a run down of extension types and the size rules that apply under Permitted Development... 

1. Single-storey rear extensions

At the back of your house, you can add a single-storey extension under Permitted Development, as long as it…

• Doesn’t exceed 4m from the original back wall (3m if it is not detached). Recent changes to PD rights mean you can now build a rear extension by up to 8m (for detached houses) and by 6m (if not detached) with prior approval under the neighbour consultation scheme;
• Is less than 4m in height;
• Is no more than half the width of the original house;
• In Northern Ireland, a single storey rear extension should be within 3.5m of the rear boundary if the house backs onto a road.

2. Two-storey rear extensions

You can build a two storey rear extension without planning permission, but it…

• Can’t go more than 3m beyond the rear wall of the existing house;
• Must be 'a minimum of 7m away from any boundary of its curtilage which is opposite the rear wall of the house being enlarged' (10m in Scotland and 10.5m in Wales);
• Has to be less than 4m high. 

If you want to add a storey to an existing single-storey extension, this won’t be possible under Permitted Development Rights if the existing addition extends beyond the rear wall by more than 3m, instead you'll have to look into acquiring planning permission for an extension.

3. Side extensions

You can build a side extension without planning permission, but only if it is…

• Single storey and less than 4m in height;
• No more than half the width of the original house (at its widest point).

A side extension would need planning permission if it extends beyond the side wall and is more than half the width of the house.

There are different rules about side extensions in Wales – for example, two-storey structures are possible under Permitted Development.

4. Rear and side extensions

Tread carefully in cases where both the rear and side wall will be pushed out, as the restrictions on both apply here – and it can get complicated! Your extension must…

• Extend no more than 6m beyond the rear wall (or 8m for a detached house);
• Be one storey, not more than 4m high;
• Have a total width that’s not more than half the width of the house.

This makes ‘infill’ extensions, where you’re filling a space between the rear and side wall to square off the footprint, doable under PD. Two separate extensions are also possible but connected, wraparound designs will exceed the width restriction and require planning permission (unless you’re in Wales, where the ‘half the width’ rule does not apply).

FAQs

How high can I build an extension without planning permission?

There are rules under Permitted Development when it comes to the height and roof of an extension. 

When you extend your home the extension can't be taller than the tallest part of the original building. The roof pitch of a two-storey extension should be the same as the pitch on the original roof, as far as is practical, too. 

The height of the eaves needs to meet certain criteria as well. The Permitted Development guidelines say: 'For the purpose of measuring height, the eaves of a house are the point where the lowest point of a roof slope, or a flat roof, meets the outside wall.'

If an extension comes within 2m of the boundary the height of the eaves must not exceed 2.5m (4m for a dual pitched roof) and 3m in any other case.

Can I extend the front of my house under PD rights?

If the front faces a road, then no, not under Permitted Development rules. You’d have to apply for planning permission for an extension. In cases where your house sits on a corner plot where the side wall faces the road, this cannot be extended under permitted development either.

If you’re desperate for any extra space at the front you can possibly gain, you could add a porch to an external door (max 3sq m) as long as it’s no higher than 3m and further than 2m away from the boundary with the road.

Balconies, verandas, a chimney, aerial or satellite dish would not be allowed under Permitted Development.  

What is a Lawful Development Certificate and do I need one?

If you choose to build an extension under PD rights, it's worth getting a Lawful Development Certificate from the local council before you start the build. This legally binding document confirms that you do not need planning permission for an extension. It's a good piece of paperwork to have, especially if you come to sell your home in the future. 

Will I need Building Regulations approval?

Even if your extension can be built under PD rules, the project will need to comply with Building Regulations. The Building Regs are there to ensure construction work is safe and meets standards. From the foundations right up to the roof, there are strict regulations that need to be met. 

A building control officer, hired either through the local council or as an independent inspector, will be needed to sign off the build against the regulations at different stages of construction.

You will need to have Building Regs drawings, which can be drawn up by an architect. Expect to pay around £700 for drawings of a single-storey extension. You will also need to factor in fees for building control application fees, any structural calculations by a structural engineer and any Party Wall Agreement fees.

Can my neighbour stop or object to my extension being built under Permitted Development Rights?

No, but it’s in your interests to maintain a good relationship with them, so it’s worth taking their views into account when planning your new extension.

If you’re going down the neighbour consultation scheme route for prior approval of a larger extension under Permitted Development, your neighbours do have the opportunity to present valid objections.

How much does planning permission cost?

If your project cannot adhere to the rules outlined above for PD rights then you'll need to submit a planning application. A fee of £206 is payable for this. In Wales it costs £190. 

Most planning applications take up to eight weeks, unless they are unusually large or complex, in which case the time limit is extended to 13 weeks. If permission is refused, you can appeal but this process can take several months, so you’re better off tweaking your plans to reach an agreement. 

If your project – or your property – is anything out of the ordinary, it’s worth hiring a planning consultant to navigate the permission minefield for you and expedite reaching an agreement to keep your project on track. Just make sure the consultant you engage is a chartered member of the Royal Town Planning Institute.

If you carry on without planning permission, you could be served with an enforcement notice that orders you to undo all the work you have done. It’s illegal to ignore this, but you can appeal against it.

The best thing to do before starting any project is to get some extension planning advice from a team of experts in the know. They can help steer you in the right direction so that building an extension gets off the ground on the right foot.