Garden room planning rules UK — the 2.5m rule, Class E limits & when you need permission

The garden office is the rare London project where the planning system is genuinely on your side: outbuildings have their own permitted development class (Class E), and a well-specified garden room usually needs no application at all. The enforcement cases we see all come from the same handful of misread rules — here they are, precisely.

The Class E rules that matter

Height within 2m of any boundary	2.5m maximum — total, including roof
Height elsewhere (dual-pitched roof)	4m maximum
Height elsewhere (any other roof)	3m maximum
Eaves height	2.5m maximum
Garden coverage (all outbuildings + extensions)	No more than 50% of the original curtilage
Position	Not forward of the principal elevation
Use	Incidental to the house — no sleeping accommodation

GPDO Schedule 2, Part 1, Class E — outbuildings

The incidental-use test

Class E covers buildings 'incidental to the enjoyment of the dwellinghouse' — offices, gyms, studios, playrooms all qualify. What doesn't: sleeping accommodation, a self-contained annexe with kitchen and bathroom, or a unit you let out. Those are primary living accommodation and need full planning permission, where they'll be assessed as a separate dwelling. A WC and basin in a garden office is generally fine; a bed is not.

When a garden room needs an application

The house is listed — Class E disappears entirely within a listed curtilage, even for a small shed.
You live in a flat — no PD rights, every outbuilding needs permission.
In a conservation area, the outbuilding would sit at the side of the house (rear positions remain PD).
Any Class E limit is exceeded — height, coverage, or position.
The use is non-incidental: sleeping, a rentable unit, or a business with regular visitors.

Building regulations: the 30m² line

Detached outbuildings under 30m² internal floor area, with no sleeping accommodation, built at least 1m from a boundary or in non-combustible materials, are exempt from building regulations. Add plumbing, exceed 30m², or build tight to the boundary in timber and the exemption narrows. Electrics must always be installed by a registered electrician under Part P regardless.

Listed curtilage and conservation-area designations are exactly what the Siteline address check surfaces — run your postcode before ordering a building.

Check an address

Do I need planning permission for a garden office in London?

Usually not: an incidental-use garden office within the Class E limits is permitted development, even in most conservation areas if placed behind the house. The exceptions are listed properties, flats, and designs that breach the 2.5m boundary-height rule.

Can I put a toilet or shower in a garden room?

A WC and basin rarely changes the planning position. A full bathroom plus kitchenette starts to look self-contained — and self-contained accommodation fails the incidental test. It also brings drainage under building regulations. Keep the spec honest to the use.

How close to the fence can I build?

Right up to it, if you stay under 2.5m total height within 2m of the boundary. Practical caveats: you'll want access to maintain the cladding, guttering must not overhang next door, and building regulations fire-spread rules apply to combustible walls within 1m of the boundary.

Do I need a Lawful Development Certificate for a garden room?

It's optional but recommended — a few hundred pounds for council confirmation that the building was lawful when built. Without one, you may be proving Class E compliance from photographs years later when you sell.

Garden room planning rules: PD, the 2.5m rule and conservation areas