What Size Extension Can I Build Without Planning Permission?

07, May, 2026

Planning permission is a daunting task for many landlords. Many are kept wondering whether they actually need planning permission or not. The answer depends on extension size, the type of property, and whether your home qualifies for Permitted Development rights.

The good news is that many single-storey extensions can still be built without full planning permission if they stay within the allowed limits.

How Far Can You Extend Under Permitted Development?

For most homes in England, you can build a rear extension without planning permission if it falls within the Permitted Development rules.

The standard limits are:

Under the Larger Home Extension Scheme, these limits increase to:

However, larger extensions still require a prior approval process through the local council, even though full planning permission may not be needed.

Don’t Measure The Wrong Point

The extension is measured from the original house. This means the property as it existed when first built, not after later alterations or previous extensions.

If your home already has an extension added by a previous owner, that space usually counts towards the total allowance.

This catches many homeowners out, especially in London, where properties have often been altered over time.

Side Extensions Have Different Rules

Rear extensions get most of the attention, but side extensions follow stricter rules. A side extension usually must:

• Be single-storey

• Not exceed 4 metres in height

• Be no wider than half the width of the original house

If the extension wraps around the rear and side together, planning permission is often required because the design falls outside standard Permitted Development rules.

Read More: rear 3 meter house extension

Height Limits Still Apply

Even if the extension depth is within the allowed range, height restrictions can still stop the project from qualifying.

In most cases, the maximum height is 4 metres. The eaves height must not exceed 3 metres near boundaries. This becomes especially important for homes with neighbouring properties close by.

Large rooflights, raised ceilings, or oversized lanterns can sometimes push a design beyond the permitted limits.

Not Every Property Qualifies

Permitted Development rights do not apply equally to every property. You may still need planning permission if your home is:

• In a conservation area

• A listed building

• A flat or maisonette

• Affected by an Article 4 Direction

Flats and maisonettes do not usually benefit from standard Permitted Development rights for extensions. A reliable agency like Denham Crescent can check local restrictions early, which is important before finalising designs.

The 6-Metre and 8-Metre Rules Explained

The larger extension scheme allows bigger rear extensions without full planning permission, but many homeowners misunderstand how it works. The process still involves:

• Submitting drawings to the council

• Notifying neighbours

• Waiting for approval through prior notification

Neighbours have the right to object during this process. If objections are raised, the council reviews how much it is impacting. So whilst it avoids full planning permission, it is not completely approval-free.

Read More: home remodelers London

Building Regulations Still Apply

This is another area that causes confusion. Even if you build an extension without planning permission, Building Regulations approval is still required. This covers structural safety, insulation, drainage, ventilation, and electrical work.

The extension must still meet current construction standards regardless of planning status.

Common Mistakes That Lead to Problems

Most issues happen because homeowners rely on assumptions instead of checking the details properly. Common mistakes include:

• Measuring from the existing extension instead of the original house

• Assuming neighbours cannot object

• Overlooking local restrictions

• Believing Permitted Development removes all approvals

These mistakes often lead to redesigns, delays, or retrospective applications later.

How to Check If Your Extension Qualifies

Before making decisions, it helps to assess the property properly. Start by checking the size of the original house and whether previous extensions already exist. Then go for local council restrictions, and check neighbouring boundaries and height limits.

A simple sketch is rarely enough for complex properties. In many cases, a proper site assessment quickly identifies whether the design is realistic.

Planning Properly Before Building Saves Time Later

Trying to avoid planning permission should never mean rushing into construction without guidance.

At Denham Crescent, we help homeowners understand what can realistically be built under Permitted Development and where planning approval may still be required. We assess the property, review restrictions, and guide the design process early so projects move forward without unnecessary delays or costly redesigns.

If you are planning an house extension and are unsure what size is allowed for your home, getting clarity early often prevents bigger problems later.