Does a detached garden office count as an extension in London?

No — a detached garden office is an outbuilding under Class E, not an extension under Class A. It has its own PD limits (2.5m eaves within 2m of boundary, 50% garden coverage) and does not consume your Class A extension depth allowance. If you later want to add a rear extension to the house, your Class A rights are unaffected by the garden office.

Can I build both a rear extension and a garden room under permitted development?

Yes — a rear extension (Class A) and a detached garden room (Class E) can both be built under permitted development, provided each complies with its respective limits. The extension must not exceed 6m depth (terraced/semi) or 8m (detached), and the garden room must not exceed 50% of the remaining garden area. The key calculation is that the extension reduces your garden area, which in turn reduces the maximum footprint available for Class E outbuildings under the 50% rule.

What is the maximum size of an outbuilding in London under permitted development?

There is no single maximum size — the 50% rule means the maximum permitted outbuilding footprint depends on your original garden area. If your original garden is 100m², you can build outbuildings totalling 50m². Height limits apply: 2.5m maximum eaves height within 2m of the boundary; up to 4m ridge height (dual pitch) or 3m (flat/mono-pitch) further from the boundary.

Does a hot tub or swim spa in the garden need planning permission?

A hot tub or swim spa is generally not development under the GPDO — it is treated as garden furniture/equipment. However, an outbuilding built to house or enclose a hot tub (a pool house or garden room) falls under Class E and must comply with the outbuilding PD rules. An in-ground swimming pool may need planning in a conservation area or where it significantly alters the character of the garden.

Outbuilding vs Extension Planning Rules London 2025 | Builderr

Do Outbuildings Have Different Planning Rules to Extensions in London?

Yes — outbuildings (sheds, garden rooms, garages) follow Class E permitted development rules in London, while extensions (rear, side, double-storey) follow Class A. Class E allows detached structures under 2.5m eaves within 2m of boundary, covering under 50% of garden. Class A allows extensions up to 6m deep (terraced/semi) or 8m (detached) without planning permission.

Class A vs Class E: what's the difference?

Class A of the GPDO covers extensions to the main dwellinghouse — any addition that is physically attached to and enlarges the house itself. This includes rear extensions, side extensions, double-storey extensions and wraparound extensions. Class E covers detached outbuildings within the curtilage — structures not attached to the main house. The key practical difference: Class A has no total coverage limit (only depth, height and width restrictions), whereas Class E limits total outbuilding footprint to 50% of the original garden. A detached garage is Class E. An integral garage (part of the main house structure) is Class A. An attached garage (separate structure butting up against the house) falls somewhere between, and its classification depends on whether it shares a wall with the main structure.

Class A extension limits in London

Under Class A, a single-storey rear extension is permitted development if: it extends no more than 6m from the rear wall of the original house (terraced or semi-detached) or 8m (detached); the height at the eaves does not exceed 3m within 2m of the boundary; the maximum height does not exceed 4m; it does not exceed 50% of the curtilage of the original house. Side extensions under Class A are more restricted: single-storey only, maximum 4m high, and the width must not exceed half the width of the original house. Double-storey extensions require planning permission in most cases (Class A only permits single-storey under PD for most configurations). The Neighbour Consultation Scheme (Prior Approval for larger extensions) allows rear extensions up to 8m (semi/terraced) or 10m (detached) if neighbours do not object within 21 days.

Can I combine a Class A extension and a Class E outbuilding?

Yes — you can combine an attached extension (Class A) with a detached outbuilding (Class E), provided each individually complies with its respective permitted development limits. The extension does not consume your Class E 50% coverage allowance, and the outbuilding does not consume your Class A depth allowance. However, where a 'link structure' connects the extension to an outbuilding, the combined structure may be re-classified as an extension to the main house, falling under Class A. A link structure that is fully glazed, enclosed and habitable is likely to be treated as an extension. An open pergola or covered path is more likely to remain separate.

When do both classes require planning permission?

Both Class A and Class E PD rights are removed or restricted in certain circumstances. Listed buildings: no permitted development rights for any works affecting the character of the building or curtilage — both extensions and outbuildings require planning and LBC. Conservation areas: Class A rear extensions are still permitted development (subject to limits), but Class A side extensions (and Class E outbuildings within the curtilage of a listed building) may require planning. Article 4 Directions: specific LPA-imposed restrictions that remove one or more classes of PD rights in defined areas — typically conservation areas in London. Always check your LPA's Local Development Framework and any Article 4 Directions on the Planning Portal.