A proposed 98 sqm home gym and storage building has failed a permitted development appeal after its owner did not explain why that much space was reasonably required.
The Inspector accepted that a domestic gym and storage could be incidental to a home. The problem was the evidence supporting this particular building, including who would use it, what equipment it would contain and what needed storing.
Inspector Thomas Shields dismissed both linked appeals, 3363978 and 3363975, at Southering, Deadhearn Lane, Chalfont St Giles, on 24th September 2026. A separate proposal for a rear extension also failed.
A home gym without the evidence to explain its size
The outbuilding would replace an open-air swimming pool enclosed by three brick walls. Retaining those walls would not turn the proposal into a minor alteration to an existing building: adding a roof and fourth wall would create a new building.
The plans labelled the approximately 98 sqm rectangular space as gym and storage. Its area was broadly comparable with the original house’s footprint, although smaller than the house as subsequently extended.
That scale was not automatically fatal. Nor did the appeal turn on a breach of the agreed dimensional and siting limits in Class E.
Applying the approach in Emin v Secretary of State for the Environment and Mid Sussex District Council, Shields distinguished a use being incidental in principle from a building of that size being reasonably required for it.
There was no adequate evidence about the number of residents who would use the gym, the proposed equipment or its layout. The nature, quantity and space requirements of the stored items were also unexplained.
The appellant additionally referred to lawn tennis, handball and five-a-side football. That did not resolve the absence of evidence about the household’s requirements.
Shields concluded that the floor area is excessive and disproportionate
in the context of this dwellinghouse. The applicant had not demonstrated, on the balance of probabilities, that the building was reasonably required for the claimed incidental purposes.
This was a refusal of a proposed lawful development certificate, not a finding that a 98 sqm outbuilding can never obtain permission. Our Class E outbuilding guide explains the separate use, size and location requirements.
The porch did not justify a brick rear extension
The second appeal concerned a single-storey rear extension with a brick finish extending across just over half the house’s width.
The house was predominantly finished in smooth cream render. A small brick porch did not make the much larger brick extension similar in appearance to the dwelling taken as a whole, as required by Class A.
There was a further problem with relying on that porch. It had been built contrary to its permission, and the appeal did not establish that the breach was lawful. Even putting that issue aside, its limited contribution did not justify the proposed rear brickwork.
Simply changing the extension to matching render would not have rescued the permitted development argument. The property is on Article 2(3) land within a National Landscape. Paragraph A.2(a) of the Class A legislation excludes development involving specified exterior cladding, including render.
Both certificate refusals were therefore upheld: one because the space required had not been demonstrated, the other because the proposed exterior materials did not satisfy the rules.
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