Outbuilding extension refusal overturned on appeal in Hillingdon.

Hillingdon refused a rear garden outbuilding extension over its footprint, height and bulk. The Inspector allowed it anyway - once the outbuilding was weighed against the size of the garden it actually sits in, rather than judged on its own.

The application

✓Site: a large, subdivided dwelling on Copperfield Avenue, Uxbridge, with an exceptionally deep rear garden backing onto Micawber Avenue.
✓Proposal: a flat-roofed extension to an existing outbuilding positioned toward the rear of the garden - submitted retrospectively, after the work was already carried out.
✓Decision: refused by Hillingdon, then allowed on appeal by the Planning Inspectorate.

Why the council refused it

Hillingdon's single refusal reason was that the outbuilding's excessive footprint, height, bulk and scale meant it wasn't a subordinate and proportionate addition to the main dwelling, causing harm to the character and appearance of both the property and the surrounding area - contrary to the council's Local Plan design policies.

What the Inspector found

The Inspector allowed the appeal outright. Owing to the considerable depth and scale of the host plot, the outbuilding - even with the extension - occupied only a relatively modest proportion of the overall garden and sat comfortably within its spacious setting. It was also positioned well away from the main dwelling and wasn't readily visible from public vantage points.

The site visit also found several outbuildings of varying sizes and forms already existing in the wider locality, reflecting an established degree of variation in such structures. Taken together, the extension read as a low-level addition rather than an unduly prominent or incongruous one - and so caused no harm to the character or appearance of the area.

Where the council's assessment fell short

A few gaps stand out when you compare the refusal reason to the Inspector's decision:

Absolute size was judged without reference to the plot it sits on. The refusal focused on the outbuilding's footprint, height and bulk in isolation. The Inspector's assessment only changed the outcome once that size was weighed against an exceptionally large garden - the same structure reads very differently on a modest plot than a generous one.

Visibility from public vantage points wasn't addressed. A "character and appearance of the area" objection is significantly weaker when the structure in question can't actually be seen from public viewpoints - a point the refusal reason didn't engage with at all.

Existing variation nearby wasn't weighed against the "disproportionate" claim. The refusal treated the outbuilding as inherently non-conforming, but the Inspector found a genuine variety of outbuilding sizes and forms already established in the wider area - undercutting the idea that this one was uniquely out of place.

What this means for other appeals

✓Argue proportionality relative to your plot, not just absolute size. If your garden or plot is unusually large, make that comparison explicit - the same footprint can be modest in one setting and disproportionate in another.
✓Provide evidence of limited public visibility if it applies. Photos or a site plan showing a structure is genuinely screened from public viewpoints directly undermines a wider "character and appearance of the area" objection.
✓Document similar variation nearby, even in gardens rather than the street. A genuine mix of outbuilding sizes and forms already established in your wider area is real evidence against a "disproportionate" or "incongruous" characterisation.

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