Glossary
Two-storey extensions and London permitted development
A double-height rear or side addition. Requires full planning.
A double-height rear or side addition. Requires full planning.
A two-storey rear extension adds space at ground and first floor. Under permitted development it is limited to 3 m depth, must be at least 7 m from the rear boundary, and the roof pitch must match the existing where practicable. It is not permitted at all in conservation areas.
Maximum 3 m beyond the original rear wall, at least 7 m between the extension and the rear boundary, eaves height matching the existing, roof pitch matching the existing house so far as practicable, and any upper-floor side window obscure-glazed and non-opening below 1.7 m. Materials must be similar in appearance.
The 7 m rear boundary rule defeats most inner London terraces, where gardens are shorter than 10 m. That, and the conservation area exclusion, is why most two-storey rear extensions in London are full applications.
More severely than single-storey work, because the impact is greater. The tests are the 45-degree rule applied to first-floor as well as ground-floor windows, the 25-degree rule in section, overlooking from new upper windows, and whether the extension is subordinate to the host building. Officers frequently accept a two-storey element only where it is set in from the flank boundary.
Foundations must carry two storeys, so they are deeper than for a single-storey extension and more likely to require piling near trees. The party wall is engaged at both levels, and the existing rear wall usually needs a substantial goalpost frame where openings are formed at both floors.
How two-storey extension plays out in Camden: London Borough of Camden (Camden Council) maintains 40 conservation areas, the Hampstead Conservation Area and the Primrose Hill Conservation Area among them, and an Article 4 direction is in force there, so permitted development cannot be assumed. Anyone dealing with two-storey extension at a Camden address is therefore working to a £548 householder application decided in 8 weeks, or a £249 prior approval over 6 weeks where two-storey extension still qualifies.
| Depth limit | 3 m from the original rear wall |
|---|---|
| Rear boundary separation | 7 m minimum |
| Roof pitch | Match existing where practicable |
| Conservation area | Not permitted development |
| Upper side windows | Obscure-glazed, non-opening below 1.7 m |
| Assessment tools | 45-degree and 25-degree rules |
Only with 7 m to the rear boundary, a 3 m depth and matching pitch — and never in a conservation area.
First-floor massing affects light and privacy far more than a single storey.
Yes, and piling is more likely where trees are within influencing distance.
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