A rear extension adds living space to the back of a house. The most common form is a single-storey kitchen-diner but two-storey, side-return and wrap-around variants are also widespread across London's Victorian and Edwardian terraces.
Rear extensions are permitted development for houses (not flats) within specific size and height limits set by the GPDO, Schedule 2, Part 1, Class A.
London is different. Conservation area coverage, Article 4 directions and listed buildings are much more common in London than the national average, and any of them can remove the PD route. Use the address-level checker before you assume PD applies.
These are the national permitted development limits set by Schedule 2 of the GPDO. If your scheme stays within every rule and no local constraint removes PD, you will not need planning permission — but you may still want a Lawful Development Certificate to prove it.
| # | Rule |
|---|---|
| 1 | Single-storey: max 4m deep for detached, 3m for semi or terraced (or up to 8m/6m under the Larger Home Extension prior approval route). |
| 2 | Maximum eaves height 3m if within 2m of a boundary. |
| 3 | Maximum overall height 4m. |
| 4 | Materials must be similar in appearance to the existing house. |
| 5 | No part of the extension may extend beyond the principal elevation fronting a highway. |
| 6 | Total extended footprint cannot exceed 50% of the original curtilage. |
| 7 | Two-storey extensions must be at least 7m from the rear boundary and no higher than the main roof. |
These are the common reasons a rear extension loses the permitted development route in London and needs a full householder application instead.
Planning outcomes vary significantly by borough. Conservation area coverage is the single biggest driver — boroughs with heavy CA coverage tend to see more rear extension proposals need a full application.
Confirm whether the property is in a conservation area, subject to Article 4 or listed. This determines whether PD is available.
Commission scaled existing and proposed plans, elevations and a site/location plan from an architect or technologist.
For complex cases, book a pre-application meeting with the council to flag issues before formal submission.
Upload drawings and supporting documents via the Planning Portal and pay the householder fee (£258 at 2026 rates).
The council runs a 21-day neighbour consultation and typically issues a decision within 8 weeks.
London range; varies with specification and site.
Householder application fee (2026). LDC fee is £129.
Statutory target for householder applications.
For a detached house, a single-storey rear extension can be up to 4m deep without planning permission. For semi-detached and terraced houses, the limit is 3m. Under the Larger Home Extension prior approval route these can extend to 8m and 6m respectively, but this route is not available in conservation areas.
In most cases, yes — conservation areas remove some of the permitted development freedoms that apply elsewhere. The Larger Home Extension route is not available and rear extensions generally need a full householder application if they exceed standard PD limits.
Yes, two-storey rear extensions can be permitted development provided the extension is no higher than the main roof, at least 7m from the rear boundary, and uses matching materials. Many two-storey extensions still require a full application because of side window overlooking or boundary proximity.
Householder applications in London are determined in around 8 weeks on average. Prior approval for Larger Home Extensions is usually decided in 42 days. Complex cases in conservation areas or on listed buildings can take 12 weeks or more.
Yes — permitted development concerns the planning system, not Building Regulations. Every new rear extension needs Building Regulations approval, typically via a Building Notice or a Full Plans application through your local authority or an approved inspector.
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