The 50% curtilage area rule — no fixed maximum size
The single most important fact about garden office size limits under Class E permitted development is that there is no fixed maximum floor area. Unlike some other planning rules that specify absolute dimensions, Class E applies a proportional test: the total area covered by buildings within the curtilage (excluding the original house) must not exceed 50% of the total area of the curtilage. This means the maximum permitted garden office size depends entirely on the size of your plot and the area already occupied by other outbuildings. For a typical London terrace with a 60m² rear garden, the maximum outbuilding footprint is 30m² — this is the largest garden office you could build if no other outbuildings exist. For a larger semi-detached property with a 150m² garden, the maximum outbuilding footprint rises to 75m². In both cases, every existing shed, garage, summer house or storage structure must be deducted from the available allowance. Builderr calculates curtilage compliance precisely at the design stage and includes a curtilage area plan in every LDC application, clearly showing the original house footprint excluded from the calculation, all existing outbuildings, and the proposed garden office — demonstrating the 50% threshold is not exceeded.
Height limits under Class E: eaves, ridge and boundary rules
The height restrictions under Class E are specific and non-negotiable. The maximum eaves height for any Class E structure is 2.5m — this applies regardless of roof type, roof pitch, or distance from boundary. The maximum overall height (to the ridge or highest point) varies by roof type: 4m for a dual-pitched or hipped roof; 3m for all other roof types including mono-pitch, flat, curved and barrel vault. Critically, a separate rule overrides both: where any part of the structure is within 2m of the curtilage boundary, the maximum overall height drops to 2.5m. This 2m-from-boundary rule is the most common cause of non-compliance in garden office designs submitted for LDC approval — a mono-pitch garden studio designed at 3m maximum height fails Class E if the rear or side wall is within 2m of the fence line. Most London rear gardens are narrow enough that positioning any structure more than 2m from all boundaries is challenging. Practically, this means many London garden offices must be designed to a 2.5m maximum height unless they can be positioned more than 2m from every boundary — which limits roofline options but can be achieved with a low-profile mono-pitch or flat-roof design.
Single storey requirement and no mezzanine rule
Class E structures must be single storey — no upper floor, loft room, or mezzanine. A mezzanine platform accessed by a ladder and used as a storage area has been accepted in some LDC decisions as not constituting an 'upper storey' — but this is fact-specific and some local planning authorities take a stricter view. A mezzanine with a fixed staircase is almost universally considered a second storey and would take the structure outside Class E, requiring full planning permission. The single-storey requirement also limits the volume of a garden office relative to a house extension: a 4m-high garden office provides approximately 3.2m internal ceiling height, which is generous, but the structure cannot be double-height or incorporate a sleeping gallery. The prohibition on sleeping accommodation is separate from the single-storey requirement — even a ground-floor sleeping area in an otherwise Class E-compliant garden studio removes its PD protection and requires full planning as an annexe.
Article 4 Directions and conservation area exceptions
Even where a garden office meets every Class E size and height condition, Article 4 Directions can remove permitted development rights entirely. London has an unusually high density of Article 4 Directions — many conservation areas are blanket-Article 4, meaning all Class E rights are removed and any outbuilding requires full planning permission regardless of size. Article 4 Directions affecting Class E outbuildings are concentrated in the inner London boroughs and their conservation area networks. In Richmond upon Thames, for example, a large proportion of residential properties in Twickenham, Richmond Hill, and Kew fall within conservation areas with Article 4 Directions removing Class E rights. The practical test is always: check the specific Article 4 schedule for your address before assuming Class E applies. A full planning application for a garden office in an Article 4 conservation area is not automatically refused — design-led applications in appropriate materials (brick, timber, or rendered finishes matching the area character) are regularly approved — but the planning timeline (8–12 weeks plus design preparation) is significantly longer than the LDC route. Where Builderr submits planning applications for garden offices in conservation areas, we always carry out a pre-application consultation with the conservation officer to agree the design approach before formal submission.
