Do I need Planning Permission to build an extension?

Whether you need planning permission to build an extension in the UK depends on the specifics of your proposed development and if it falls under “permitted development rights.” Many smaller extensions can be built without needing a full planning application, but there are strict rules and conditions that must be met.

Here’s a breakdown of key considerations:

1. Permitted Development Rights (PDRs):

What they are: PDRs allow homeowners to make certain changes to their properties without applying for planning permission, provided the work meets specific criteria.
Benefits: Saves time and money by avoiding the planning application process.
Crucial point: PDRs generally apply to houses, not flats, maisonettes, or other buildings.
2. When you generally don’t need planning permission (under PDRs):

Single-storey rear extensions:

Detached houses: Can extend up to 4 meters from the original rear wall.
Other houses (semi-detached, terraced): Can extend up to 3 meters from the original rear wall.
Height: Maximum height of 4 meters (pitched roof) or 3 meters (flat roof).
Larger single-storey rear extensions (with “prior approval”): You can extend further (up to 8m for detached, 6m for others) but must notify your local council and go through a “Neighbour Consultation Scheme.” If neighbours object, the council will assess the impact.
Two-storey rear extensions:

Can only extend up to 3 meters from the original rear wall.
Must be at least 7 meters from the rear boundary.
The roof pitch should match the existing house as far as practicable.
Upper floor windows in side elevations must be obscure-glazed and non-opening (unless the opening part is 1.7 meters or more above the floor).
Side extensions:

Must be single-storey.
Cannot exceed 4 meters in height.
Must not be wider than half the width of the original house.
Not permitted on “designated land” (see below).
General rules for all permitted development extensions:

No more than half the area of land around the “original house” (as it stood on 1 July 1948 or when first built) can be covered by additions or other buildings (including sheds and outbuildings).
No extension forward of the principal elevation (front) or side elevation facing a highway.
Materials used should be similar in appearance to the existing house.
If the extension is within 2 meters of a boundary, the maximum eaves height should be no higher than 3 meters.
No verandas, balconies, or raised platforms (above 300mm high).
3. When you do need planning permission:

If your extension exceeds any of the PDR limits.
If your property is:
A listed building (you’ll also need listed building consent).
In a Conservation Area, National Park, Area of Outstanding Natural Beauty (AONB), or other “designated land” (PDRs are often more restricted in these areas).
Subject to an Article 4 Direction from your local council, which removes specific permitted development rights.
If you are building a front extension (these generally require planning permission).
If the materials used are not similar to the existing house.
If any part of the works are higher than the highest part of the existing roof.
If the eaves of the extension would be higher than the eaves of the existing house.
4. Other important considerations:

Building Regulations: Even if you don’t need planning permission, almost all extensions will require Building Regulations approval. These cover structural stability, fire safety, insulation, drainage, etc.
Party Wall Act: If your extension affects a shared wall with a neighbour, you’ll need to serve a Party Wall Notice.
Lawful Development Certificate (LDC): If you want absolute certainty that your proposed extension falls within permitted development rights, you can apply to your local council for an LDC. This provides formal confirmation that the work is lawful and won’t require planning permission.
Recommendation:
It is highly recommended to check with your local planning authority or consult with a qualified architect or planning consultant before starting any work. They can provide specific advice based on your property’s location and your proposed plans, helping you avoid potential legal issues or enforcement notices.