20/06/2026
KJP Architecture - Explainer Series 3
So, you have decided you do want an extension — and you are clear on what you are trying to achieve.
The next step is understanding what type of planning approval is required and which route is right for your project.
What do you need for a house extension?
Many homeowners assume extensions always require Planning Permission.
Sometimes that is correct — but many fall under Permitted Development.
What is Permitted Development?
Permitted Development (PD) is a set of rights granted by the UK Government that allow certain works to be conducted without applying for full planning permission.
Think of it as a fast-track route — fewer delays, less red tape — if you meet the rules.
•Permitted Development Rights (PDR)
Some extensions and loft conversions can proceed without planning permission, but only if they meet strict limits on:
Size and projection
Height and eaves level
Distance to boundaries
Materials
Percentage of garden built over
If just one of these limits is exceeded, planning permission is usually required.
There is detailed technical guidance available from the Government, but interpretation is key — small measurement differences can change everything.
Where an extension complies with PDR, we always recommend applying for a Certificate of Lawful Development.
This provides written confirmation that the works are lawful — invaluable for future sales, remortgages, and general peace of mind.
Certificate applications typically take around 6 weeks.
• When PDR Do Not Apply
Permitted Development Rights can be restricted or removed if:
The property is in a Conservation Area
The building is listed
It is a flat or maisonette
Previous extensions have already used up allowances
An Article 4 Direction or planning condition applies
In some cases, the Prior Approval route may still be available.
Understanding which route applies at the outset can save time, cost, and frustration later.
If you are unsure, that is exactly what we are here for.
