Do I need planning permission for an extension?

The short answer

Some house extensions need a planning application and some can be carried out under permitted development rights instead. It depends on the property itself, the design of the extension and whether any local restriction applies. Building Regulations are a separate approval and usually apply either way, so an extension that does not need planning permission can still need Building Control involvement.

Key points

Planning permission and Building Regulations are two different systems with different rules.
Permitted development rights allow some work without a planning application, but they are subject to limitations and conditions.
Rights can be reduced or removed for flats, maisonettes, listed buildings, converted properties and homes in designated areas.
Only your local planning authority can confirm what applies to your specific address.
Being clear about what you are actually building makes every later conversation — planning, Building Control and builder quotations — far easier.

Published by Kezariq Ltd. See the source links below for official guidance.

When an extension is likely to need planning permission

Planning control is about the effect a development has on the area and on neighbours: size, siting, height, appearance, overlooking and loss of light. The larger and more visible an extension is, the more likely it is that a planning application will be required.

Extensions that go beyond the limits set for permitted development.
Work to a flat, maisonette or a property created by conversion, where householder permitted development rights generally do not apply in the same way.
Work to a listed building, or work affecting a building in a conservation area.
Anything a previous permission or planning condition already restricts.

Permitted development at a high level

Permitted development is a national grant of planning permission for certain types of work. It is not a blanket exemption. Each class of permitted development comes with limitations on things like size, height, position and materials, and with conditions that must be met.

Because those limits are technical, property-specific and change over time, this guide deliberately does not restate them as fixed figures. Check the current rules on the Planning Portal and confirm the position for your property with your local planning authority.

Why your property's circumstances matter so much

Two identical designs on two different houses can end up with different answers. That is normal, and it is why generic online figures are unreliable.

Previous extensions may have already used up what the property is allowed.
The property type — house, flat, maisonette or converted dwelling — changes what rights exist.
Where the extension sits in relation to boundaries and the highway can matter.
Planning conditions attached to an earlier approval can remove rights entirely.

Conservation areas and Article 4 directions

In conservation areas, national parks, Areas of Outstanding Natural Beauty (National Landscapes) and other designated areas, permitted development is more limited and additional controls can apply.

Separately, a local planning authority can make an Article 4 direction that withdraws specified permitted development rights in a defined area. Where one applies, work that would normally be permitted development needs a planning application. Article 4 directions are local, so the only reliable check is your own council.

Building Regulations are a separate question

Building Regulations set standards for the construction itself — structure, fire safety, insulation, ventilation, drainage, electrical safety and more. They apply to most extension work regardless of whether planning permission was needed.

It is common for an extension to need Building Control but no planning application, and it is possible to need both. Treat them as two separate approvals to plan for.

When you may still need professional or local authority advice

Guides like this one help you frame the question. They do not replace advice on your specific property.

Structural alterations, such as removing or opening up a load-bearing wall, need a suitably qualified structural engineer.
Listed buildings and unusual sites usually need input from an architect or planning consultant.
Where the answer is genuinely uncertain, a Lawful Development Certificate application to your council gives you a formal written position.
Work near or on a shared boundary may bring the Party Wall etc. Act 1996 into play.

Things to check

Whether your property is a house, a flat, a maisonette or a converted dwelling.
Whether the property is listed, or in a conservation area or other designated area.
Whether an Article 4 direction covers your street.
Whether earlier extensions or planning conditions have already used or removed rights.
What your local planning authority's website says about pre-application advice.
Whether the work will also need Building Regulations approval — it usually will.

Common questions

Does permitted development mean I do not need any approval?

No. Permitted development only relates to planning. Building Regulations, and other legislation such as the Party Wall etc. Act 1996, can still apply to the same work.

Who can confirm whether my extension needs planning permission?

Your local planning authority. If you want a formal written answer that the work is lawful without permission, you can apply for a Lawful Development Certificate.

Not sure which rules may apply to your project?

The KEZARIQ Planning Assessment asks about your property and your proposed work, then produces a written report setting out the areas to check, the risks to be aware of and a prioritised list of next steps. It is a starting point for your own enquiries, not a planning decision.

Assessment Project Report — £10.99

Assess your project with KEZARIQ

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Important

This guide is general information for UK homeowners. It is not legal, planning, structural or professional advice, and it does not take account of your individual circumstances. Rules change and vary between England, Wales, Scotland and Northern Ireland, and by local authority.

KEZARIQ provides guidance and documents you complete and review yourself. It does not manage your project, carry out professional services, or replace an architect, surveyor, structural engineer, planning consultant or other competent professional where one is required. Nothing here guarantees planning permission, Building Regulations approval, prices, contractor performance or any project outcome. You remain responsible for your own project and decisions.