Applying for planning permission can be one of the most painful parts of starting your extension, especially if you have never been through the process before.

But fear not, we have answered the most common questions around planning permission for extensions to help you get off to a smooth start!

How much does it cost to apply for planning permission for extensions?

The cost for the planning application alone for an extension will be £172¹ for a Full Planning Application, or £86 for a Lawful Development Certificate, which is appropriate where you think you may not need planning permission but want to make certain.

However, you will pay more in professional fees for the drawings and if you have a professional submitting the plans on your behalf. For an average extension with a build cost of around £30,000 – £40,000 you should budget around £1,000 – £2,500 for planning permission drawings. The fees depend on the scale of your project (whether you are having a simple extension or a design makeover!) and also where you live in the UK.

working with an architect

Kitchen extension by TW10 Architects

How long does planning permission for extensions take to be approved?

The statutory period the planners have to make a decision is 8 weeks. If your plans are approved you can start the work immediately (subject to other applications such as the Party Wall Act) and you have up to 3 years to begin the work.

Do I always need to apply for planning permission for an extension?

The great news is that there are many instances where extensions fall within permitted development, meaning you don’t need planning permission!

This is very dependent on the area you live in, the scale and style of work you are carrying out and also your style of property. Always check with your local authority before you go ahead with your project.  Check out our guide to extensions to understand what you can often do within permitted development.

Remember that even if you don’t need to apply for planning permission for your extension, you must always comply with building regulations and also make sure that you consider the impact of your project on your neighbouring properties, including the Party Wall Act and Right of Light.


Photo by Chris Snook. Kitchen extension by Black Oak Builders.

Do I need to let my neighbours know I am applying for planning permission?

The council will contact your neighbours on your behalf and let them know about your plans. However, if you have your neighbours on side then it is more likely that the planning permission process will run smoothly.

It’s always helpful to chat to your neighbours about your proposed extension, even before you have met with the architect. This way you can have the opportunity to design your extension to work for everybody.

Can I submit the plans myself?

Absolutely yes – and this will also save you additional professional fees! You can even complete the drawings yourself if you have the time and inclination to do so. However, many people do choose a professional to complete the drawings and submit the application as this can take out some of the work and pressure.

If your extension is straightforward and you would like a professional to do the drawings, go for an architectural technologist. If you need some creative help then an architect (registered with ARB, is the best route.

If you need more help, check out our Expert Advice on Planning Permission!

¹Note these are the cost in England and they vary slightly throughout the rest of the UK.