Permitted Development: The Size Limits That Actually Matter
Most single-storey rear extensions are covered by Permitted Development rights, meaning no planning application is required — but the limits are specific and worth knowing before assuming a project qualifies:
| Extension type | Property type | Permitted Development limit |
|---|---|---|
| Single-storey rear extension | Detached house | Up to 8m depth |
| Single-storey rear extension | Semi-detached / terraced | Up to 6m depth |
| Two-storey rear extension | Any house type | Up to 3m depth, height and boundary rules apply |
Extensions beyond 3–4 metres (depending on property type) trigger a "neighbour consultation scheme" under Permitted Development — still not a full application, but neighbours are formally notified and can object on impact grounds. Height, eaves, and roof pitch also have specific limits that apply regardless of depth. See our side-return extension planning permission guide for how these rules apply specifically to side-return projects, which follow a different set of conditions.
When You Definitely Need Full Planning Permission
- Two-storey extensions exceeding Permitted Development depth and height limits
- Extensions forward of the building line facing a road
- Properties in a Conservation Area or subject to an Article 4 Direction — see our Article 4 Direction guide for which parts of Greater Manchester this affects
- Flats and maisonettes — Permitted Development rights for extensions generally don't apply to flats at all
- Extensions that would exceed 50% of the original garden area once combined with previous extensions and outbuildings
The Application Process, Step by Step
Pre-Application Advice (Optional but Recommended)
Most Greater Manchester councils offer a paid pre-application advice service, which flags major concerns before a full application is submitted. For anything borderline — a larger extension, an unusual design, a sensitive location — this step frequently saves time overall by catching issues early.
Validation
The council checks the application is complete — correct drawings, forms, and fee — before the statutory clock starts. An incomplete submission is one of the most common causes of delay at this stage.
Consultation
Neighbours and, where relevant, parish or ward councillors are notified and given a period to comment. Most straightforward householder applications don't receive objections, but where they do, this stage can extend the timeline.
Case Officer Assessment
A planning officer assesses the application against local policy. For most householder extensions this is a delegated decision (no committee involved), which is faster than applications requiring committee sign-off.
Decision
Approval, refusal, or approval with conditions. Conditions commonly require material samples or landscaping details to be agreed before work starts — these need discharging separately and can add time if not anticipated.
Planning Permission vs Building Regulations: Don't Confuse the Two
Planning permission and Building Regulations approval are separate processes, and this is one of the most common points of confusion for homeowners. Planning permission concerns whether the extension is allowed at all — its size, position, and impact on neighbours. Building Regulations concerns whether the construction itself is structurally sound, insulated properly, and fire-safe. Every extension needs Building Regulations sign-off, whether or not planning permission was required.
Don't Forget the Party Wall Act
Separately from planning permission, work on or near a shared wall with a neighbour is covered by the Party Wall Act, which requires formal notice regardless of whether the extension needs planning permission. This applies to most extensions on terraced and semi-detached properties. Our side-return extension guide covers this process in more detail, since it applies to nearly every side-return project.
What Actually Causes Delays or Refusals
The most common reasons a straightforward extension application stalls or gets refused aren't usually about the extension itself — they're about how the application was prepared. Inaccurate or incomplete drawings, insufficient detail on materials, and a design that doesn't address an obvious neighbour-impact concern (loss of light, overlooking) are the recurring issues. A well-prepared application, with a clear supporting statement addressing these points upfront, has a materially better chance of a smooth first-time approval. See our house extension cost guide for how planning route affects overall project cost and timeline.