Appeal 3359723

The appeal is dismissed.

The main issue is the effect the proposed extension would have on the character and appearance of the host dwelling and its semi-detached neighbour in the context of the surrounding Harlington Village Conservation Area (CA).

Policies BE1 and DMHB11-12 of the adopted Hillingdon Local Plan (HLP) and D3 of the adopted London Plan generally require new development to be of high-quality design to integrate well with the surrounding area.

Policies HE1 and DMHB4 of the HLP, consistent with national planning law and policy, require development to preserve or enhance conservation areas.

Policy DMHD1 of the HLP contains detailed stipulations relating to side and rear extensions in conservation areas. These include that a side extension does not exceed half the width of the existing property and is subordinate to and respects the design and materials of the existing house; there is to be no adverse cumulative impact on the character, appearance or quality of the street; and a satisfactory relationship with adjacent dwellings is to be achieved.

All these policies are essentially consistent with the National Planning Policy Framework (NPPF), wherein less than substantial harm to a designated heritage asset such as a conservation area must be weighed against countervailing public benefits.1 1 National Planning Policy Framework 2024 paragraph 215

Policy DMHD1 includes a range of other criteria, with which the proposed extension would comply. There is no evidence that it would cause unacceptable loss of outlook at neighbouring properties, or that car parking or garden space would become inadequate, and no trees or hedges would be harmed. Flat roofs would be avoided and the front wall of the new extension would be appropriately set back.

More importantly however, the cumulative effect of the proposed and substantial existing extensions to this semi-detached property would be an increase in frontage width over the original vastly in excess of the 50% policy maximum. The further extension now proposed would significantly magnify the degree to which the semi-detached pair of dwellings has become visually unbalanced.

I recognise that there would be a number of mitigating circumstances. The appeal site is a corner plot with inherent potential for a sideways built extension. The extension would replace an existing outbuilding and be partly screened by the flank boundary wall. The extension now proposed has been carefully designed with a mono-pitch roof, and in an architectural style and finishing materials matching those of the present house.

I accept that there is little consistency of style within the Village Conservation Area as a whole, and that the proposed extension would be sufficiently well separated by distance and the intervening [address] to avoid any adverse impact on the setting of the nearby Listed White Hart public house.

However, the extension would still be visible in public views from [address] and [address] within the Conservation Area. I consider that the additional degree of visual imbalance created by the appeal development, within this prominent, semi-detached pair of dwellings, would harm their character and appearance. In turn, it would also harm the character and appearance of the wider street scene.

For these reasons I consider that the proposed development would be of insufficient design quality and, as a result, would not integrate well with the surrounding area and would fail to preserve the character or appearance of the Harlington Village Conservation Area as whole, as required by the development plan provisions summarised above.

On balance, I therefore see the proposed development as giving rise to less than substantial harm to the Conservation Area, as a designated heritage asset, to be weighed against public benefits, in the terms of the NPPF.

The development would secure a degree of public benefit by adding a larger family home to the local housing stock. There would also be a measure of personal benefit in providing multi-generational accommodation, including for the elderly, albeit the level of need in the latter regard is not documented and this transient family need, whilst material, can be afforded little planning weight on the evidence to this appeal.

On a balance of judgement, any positive benefit is of insufficient importance to outweigh the less than substantial harm to the Harlington Village Conservation Area, which I have identified.

I conclude, overall, that the proposal is contrary to the development plan as a whole and that this appeal should therefore be dismissed.