Appeal 3330083

The appeal is dismissed.

At the time of my visit, construction works were ongoing. However, they were not complete, and I have dealt with the scheme before me as a proposal, rather than as the retention of existing development.

The main issue is the effect of the proposed development on the character and appearance of the host property and the area, including whether it would preserve or enhance the character or appearance of the Osterley Park Conservation Area (‘the OPCA’).

Section 72(1) of the Planning (Listed Buildings and Conservation Areas) Act 1990 states that, in respect of development affecting conservation areas, special attention shall be paid to the desirability of preserving or enhancing their character or appearance.

The host forms one half of a semi-detached pair, which is located towards the end of a cul-de-sac. Its style and design features, which include bay windows and a central chimney stack, are typical of the road, and in common with most nearby properties it is finished in a mix of render, brick and tiles. The buildings’ appearance, including their principally sloped roof form, along with their spacing and their set back from the highway, give the area a cohesive appearance, which contributes to the significance of the OPCA.

The proposed side dormer would be set only just up from the host’s eaves and it would continue its existing ridgeline. As a result, notwithstanding its set back from the host’s front face, it would be a fairly bulky and prominent feature which would give the property a ‘top-heavy’ appearance. [name] observed a scattering of nearby roof level alterations, including some hip to gable extensions, in streetscene views most of the properties retain their original, simple, hipped roofed form. This side dormer would therefore also be at odds with the prevailing character of the area.

It would thus fail to comply with the advice at paragraph 4.10 of the [name] Planning Document 2017 (‘SPD’) that roof extensions should be subservient to the scale of the roof slope and secondary to its size, and should have regard to the streetscene and the character of the property. It would also conflict with its advice at paragraph 6.2 that within conservation areas side dormers should be small and in keeping with the style of the building.

In its favour, I observed that No 24 has a similar side dormer extension, and that this scheme would therefore help to re-balance the pair. The Council maintains that as that dormer does not benefit from planning permission, it cannot be considered to set an appropriate precedent. I have no conclusive evidence with regards whether or not that dormer is lawful. I therefore conclude that the proposed side dormer would cause only limited harm to the character and appearance of the area.

Turning to the proposed rear dormer, although it would be set below the host’s ridge and up from its eaves, this would be by less than the amount advised at paragraph 6.2 of the SPD; and its scale, at well over half the width of the original roof, would also be contrary to that advice. It would have a very rectilinear form and bulk, and in combination with the proposed side dormer, it would add to the property’s top-heavy appearance. Although it would not be visible in the streetscene, the harm that it would cause would be evident from nearby gardens and the playing fields to the rear.

Additionally, the rear dormer would extend beyond the host’s original hipped roof to attach to the proposed side dormer. Taken together, the dormers would thus ‘wrap-around’ the host, resulting in a very bulky roof level form, which would be at odds with the SPD’s advice at paragraphs 4.10 that roof extensions should be independent of each other.

Some nearby properties on this part of [address] have rear dormers, and some have roof level extensions to the side. However, taken as a whole, the combined impact of the roof level extensions to the side and to the rear of this property would largely subsume its original, simple, hipped roofed form.

Notwithstanding the proposed use of matching materials, the scheme would therefore significantly harm the character and appearance of the host property and the area. It would thus conflict with those parts of Hounslow Local Plan 2015-2030 (2015) (‘HLP’) Policies CC1, CC2 and SC7 which require high quality design that complements the original building, maintains the character of the streetscene, and responds to the grain, massing and height of surrounding buildings. It would also conflict with the advice in the SPD.

HLP Policy CC4 requires proposals to conserve, and take opportunities to enhance, the character of conservation areas, considering matters such as grain, scale, form and proportions; and states that extensions should be sympathetic to the original building in terms of scale and form. The scheme would conflict with that approach.

In accordance with the National Planning Policy Framework (December 2023) (‘Framework’), I have attributed great weight to the conservation of this designated heritage asset. However, as the harm caused to it would be ‘less than substantial’, I am required by the Framework and by HLP Policy CC4 to weigh it against public benefits.

In this case, whilst I have not been directed to public benefits, the scheme would provide additional accommodation, and there would be a modest economic boost during construction. However, the limited public benefits would not outweigh the harm that I have found. Consequently, the scheme would also conflict with HLP Policy CC4 and with the Framework.

There are no material considerations that would outweigh the conflict with the development plan, and having regard to all other matters raised, the appeal is therefore dismissed.