Single Storey Extension: Permitted Development Rules

The specific permitted development rules for single storey rear and side extensions in England, including sizes, heights and conditions.

Single storey extensions are one of the most popular home improvement projects and many can be built under permitted development rights without needing planning permission. Here are the detailed rules.

Rear Extensions

Standard Limits

Detached houses: maximum projection of 4 metres from the original rear wall
Semi-detached and terraced houses: maximum projection of 3 metres
Maximum eaves height: 3 metres
Maximum overall height: 4 metres

Larger Extensions Under Prior Approval

You can build a larger single storey rear extension under the prior approval (neighbour consultation) process:

Detached houses: up to 8 metres
Semi-detached and terraced houses: up to 6 metres

Prior approval costs £120 and requires the council to consult adjoining neighbours. If no objections are received within 21 days, the council must approve the development. If objections are received, the council will assess the impact and make a decision.

Side Extensions

Must be single storey
Must not exceed half the width of the original house
Maximum eaves and ridge height: 4 metres
Must not extend beyond the rear wall of the original house by more than the standard rear extension limits

In conservation areas, national parks and AONBs, side extensions are not permitted development - you will need planning permission.

Wraparound Extensions

A wraparound extension (rear and side combined) is technically treated as two separate extensions for PD purposes. Each element must comply with its own limits. The combined area must not cover more than 50% of the garden.

Key Conditions That Apply to All Single Storey Extensions

Must not extend forward of the principal elevation (the front of the house facing the road)
Materials should be similar in appearance to the existing house
Total area of all outbuildings and extensions must not cover more than 50% of the curtilage (garden area)
The extension must not result in a separate dwelling
No verandas, balconies, or raised platforms

What Counts as the "Original" House?

The rules refer to the "original house" - this means the house as it was first built, or as it stood on 1 July 1948 (whichever is later). Any previous extensions count against your permitted development allowance, even if they were built by a previous owner.

Building Regulations

Even if your extension is permitted development and does not need planning permission, you will still need building regulations approval. This ensures the construction meets standards for structural safety, fire protection, insulation, ventilation, and drainage. You will need to submit a building control application to your local authority or an approved inspector before work starts.

Tips

Measure carefully - going even slightly over the limits means you need full planning permission
Get a Lawful Development Certificate before starting, especially for larger PD extensions
Check whether an Article 4 Direction applies in your area
Talk to your neighbours before building - even if you do not need their permission, good relationships matter