The interest rates in building an extension onto the home are continuously on the rise, even before we were even hit by a pandemic, the view that a homeowner should improve rather than move is as popular as it has ever been.
So, with more interest as ever, the answers a lot of people are after have a lot to do with the subject of planning permission.
The question we’ll be focusing on answering today is “When do I need planning permission for a house extension?”. Let’s break this down.
In a lot of instances, your extension to your house can fall under the Permitted Development act, so you wouldn’t actually need to gain any permission or submit any application for planning permission for you extension, there are however a few parameters that your extension would need to meet before knowing if your plans fall under this act.

What should I consider when determining whether I need planning permission or not?

When you’re reviewing your options when it comes to planning permission, keep some of the below points in mind:
  • The size of the extension should be no more than half the area of land around the original house. By original house, we mean when it was first built, not just the time since you’ve owned the property. So it would be beneficial to research as to whether any previous owners may have already made waves to improve the property.
  • The placement of your extension cannot be built near a public highway either by front elevation or side without needing to first obtain planning permission. If your extension, once finished finds itself nearer a public highway consult your local authority.
  • If you extension happens to be higher than the highest part of your existing roof, you would need to obtain planning permission.
  • Generally single store rear extensions that extends no more than 3m should happily fall under permitted development (this is however subject to listed buildings and conservation areas).
  • The maximum height of a single-storey rear extension should be 4m to avoid having to get planning permission for an extension.


This list is by no means exhaustive and we will always recommend seeking the advice of a planning officer within your relevant local authority before going ahead with any construction methods. The above advice is mainly with a house owner in mind, therefore if you’re looking for information on flats, maisonettes or listed building extensions, we would recommend speaking to your local authority to double check.
The rules on permitted development are constantly updated so definitely make sure to keep yourself up to date and informed throughout your research
Planning permission can sometimes take up to 12 weeks. You spend all that time waiting, and then still have to get prices from contractors for your future project. Sorting through a stack of estimates and the back and forth of negotiating pricing will create even more delay. It’s no wonder that so many extension projects can feel out of reach or get pushed to the bottom of our lists of priorities.
Having one of our experts come to perform your site survey means we have the opportunity to assess your property’s suitability for adding a HAB in a fraction of the time. We will be able to discuss any site-specific queries you might have, as well as offer experience-based advice. We will also ensure that your HAB is within permitted development before commencing.
When we developed Habattach we made sure that the HAB’s themselves would fall within permitted development in most situations. It was important to use for the Habattach process to be as streamlined as possible and by taking advantage of the permitted development allowances, this means we’re able to keep it simple. If there are situations where a client’s property does not qualify for the permitted development act, we take care of this too and make sure to build this into the cost of our HAB which means we’re able to avoid over complicating the process for all of our clients no matter their planning permission needs!
If you would like to find out more about our modular extensions, head on over to for more information or drop us an email to
Exterior Example - Living Room Layout - Hab 2 Prefab Extensions
Hab 2 Interior Example - Living Room Prefab Extension

If you would like to find out more about our modular extensions then head on over to for more information or drop us an email to

We can install our prefab extensions anywhere the UK including London, Oakham, Manchester, Northampton, Leicester, Coventry, Cambridge, Bedford, Lincoln, Birmingham and more.