Do I need planning permission for a single-storey rear extension?

Often no. A single-storey rear extension is frequently permitted development if it stays within the national size, height and eaves limits and your permitted development rights have not been removed. In conservation areas, on flats, or beyond the limits, you will need a householder planning application.

How long does planning permission take in the UK?

A householder application has a statutory target of eight weeks from validation. In practice it can take longer if the authority is busy or asks for more information, so allow up to twelve weeks and apply early.

What happens if I build without permission?

The council can serve an enforcement notice requiring you to undo the work, and unauthorised work makes a property hard to sell. It is far cheaper to confirm the position first, either through a Lawful Development Certificate or a planning application.

Is planning permission the same as Building Regulations?

No. Planning permission controls what you build and how it looks; Building Regulations control how it is built safely. Many projects need both, and you should never assume that having one means you have the other.

Homeowners

Do I Need Planning Permission? A Plain-English UK Guide

A clear walkthrough of when UK projects need planning permission, when they do not, and how to avoid the expensive mistakes.

Reviewed 10 June 2026 · 7 min read

Do I Need Planning Permission? A Plain-English UK Guide — illustrative image — Illustrative imagery. Not a specific AH Architecture project.

Most stalled projects do not fail because the design was wrong. They fail because the planning position was never properly understood at the start. This guide explains, in plain English, when you need planning permission in the UK and when you do not.

It is general guidance for England. Wales, Scotland and Northern Ireland differ, and your local planning authority can apply local rules on top. When the stakes are high, a short feasibility review is far cheaper than a refusal.

What planning permission actually is

Planning permission is your local council’s consent for a change to a building or land. It controls what is built and how it looks and is separate from Building Regulations, which control how it is built safely.

You can need one, both, or neither depending on the work. A loft conversion, for example, often needs Building Regulations approval even when it does not need planning permission.

When you usually do NOT need permission: permitted development

Many house extensions and alterations fall under "permitted development rights", a national grant of permission with size and position limits. Stay within the limits and you can build without a planning application.

Common examples that are often permitted development on a typical house:

→ Single-storey rear extensions within the depth, height and eaves limits
→ Loft conversions within the volume allowance and not on the principal elevation
→ Outbuildings and garden rooms within height and coverage limits
→ Internal alterations that do not change the use or the exterior

When you DO need planning permission

You generally need a full or householder planning application when the work exceeds permitted development limits, changes the use of a building, or affects a protected setting.

Permitted development rights are also removed or restricted in many situations, so always check before you rely on them.

→ Larger or two-storey extensions, and most new dwellings
→ Flats and maisonettes (permitted development for houses does not apply)
→ Conservation areas, Areas of Outstanding Natural Beauty and National Parks
→ Listed buildings, which also need separate listed building consent
→ Where an "Article 4 Direction" has removed permitted development rights

Prove it: the Lawful Development Certificate

If your project is permitted development, it is worth applying for a Lawful Development Certificate. It is a formal confirmation from the council that the work is lawful, and it protects you when you sell.

Without it, a future buyer’s solicitor can hold up the sale while you scramble for evidence years after the work is done.

How long it takes and what it costs

A householder planning application typically has a statutory determination period of eight weeks from validation, though busy authorities and requests for more information can extend this.

Application fees are set nationally and change periodically; check the current householder fee on gov.uk or your local authority’s planning portal. The bigger cost is usually the professional drawings and reports, not the fee itself.

Frequently asked questions

Do I need planning permission for a single-storey rear extension?: Often no. A single-storey rear extension is frequently permitted development if it stays within the national size, height and eaves limits and your permitted development rights have not been removed. In conservation areas, on flats, or beyond the limits, you will need a householder planning application.
How long does planning permission take in the UK?: A householder application has a statutory target of eight weeks from validation. In practice it can take longer if the authority is busy or asks for more information, so allow up to twelve weeks and apply early.
What happens if I build without permission?: The council can serve an enforcement notice requiring you to undo the work, and unauthorised work makes a property hard to sell. It is far cheaper to confirm the position first, either through a Lawful Development Certificate or a planning application.
Is planning permission the same as Building Regulations?: No. Planning permission controls what you build and how it looks; Building Regulations control how it is built safely. Many projects need both, and you should never assume that having one means you have the other.