Two-storey rear extensions always need planning permission — they are not permitted development. Here’s how the application works, what councils assess, and the key design rules.
A two-storey (or more) rear extension to a dwellinghouse requires a full planning application — it is not permitted development under Part 1 of the GPDO 2015. Only single-storey rear extensions are permitted development (subject to size limits). Two-storey rear extensions are assessed against the council’s Local Plan policies. Key design considerations include the 45-degree rule, impact on daylight and outlook for neighbours, and the roof form matching the host dwelling. That said, two-storey rear extensions are commonly approved where they are well designed and comply with local policy.
Part 1 of the GPDO 2015 grants permitted development rights for extensions to dwellinghouses. Class A covers single-storey rear extensions (up to 4m for detached houses, 3m for others under the standard allowance, or up to 8m/6m under the Larger Home Extension Scheme with neighbour notification). Class B covers roof extensions (dormers).
Critically, Class A of Part 1 only permits additions that are single storey. A two-storey rear extension — even a modest one — falls outside Class A and cannot be permitted development. This rule applies whether the extension is attached to the rear of the house only or wraps around the side.
For a two-storey rear extension, a householder planning application is required. The key steps:
| Condition | Detail |
|---|---|
| Application fee | £528 (householder application, England, 2025) |
| Determination period | 8 weeks (or agreed extended period) |
| Neighbour notification | All adjoining neighbours — 21 days to comment |
| Decision | Delegated officer decision in most cases; referred to committee if significant objections |
| Appeal | Right of appeal to Planning Inspectorate within 12 weeks of refusal |
Most councils assess two-storey rear extensions against their Residential Design SPD or equivalent local guidance. The most important factors are:
| Option | Pros/Cons |
|---|---|
| Single-storey rear | Permitted development (up to limits). No planning application needed. |
| Two-storey rear | Needs planning permission. More floor space. Can add more value. |
| Loft conversion | May be PD (Class B dormer). Adds floor space without affecting garden. |
Extensions, loft conversions, outbuildings, solar panels — our complete guide covers everything you can build without planning permission.
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