Appeal 3329286

The appeal is dismissed.

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 Isleworth Riverside Conservation Area (‘the IRCA’).

Planning permission was previously granted at this site for a single storey rear and side infill extension and a rear roof extension (Ref: 00783/1/P1) (‘previous permission’). Compared to it, the appellant describes this proposal as comprising a larger dormer, and an additional 1 metre width at first and ground floor.

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.

Policy CC4 of the Hounslow Local Plan 2015-2030 (2015) (‘HLP’) requires development proposals to conserve and take opportunities to enhance the character of conservation areas, taking account of matters such as grain, scale, form and proportions. It continues that extensions should be high quality and in keeping with the character of the building and surrounding area, having regard to the scale and form of the original building.

According to the Isleworth Riverside Conservation Area Appraisal (2021) the site falls within the Talbot Character Area. It describes it as comprised of late Victorian residential streets which are mostly laid out as long, rectangular blocks of two storey terraces, set back a short distance from the pavement, with a dense, compact, fine urban grain. It lists as a threat to the IRCA development which fails to respect the character of the area, having regard to matters such as scale, detailing, and the historic relationship to the street.

At pages 2 and 3 of his statement the appellant provides photographs of nearby large rear dormers which are visible in the public realm. Whilst some of these may have been constructed under permitted development rights prior to the inclusion of this area within the IRCA, they are now part of the area’s character. That said, I also observed that many of the terraces finish with a narrow side wall and gable, with no prominent bulky rear roof extension, thus preserving their simple, original form in the streetscene.

Viewed from the highway, the host’s form, style, detailing and materials are typical of [address]. However, unlike the nearest properties in this row, many of which have single storey rear projections, it has a two-storey rear extension which spans roughly two thirds of its face. I observed on my visit that a single storey rear extension is also under construction.

The proposed two storey flat-roofed side extension would fill in the space next to the existing two storey rear projection, resulting in all of the original property’s rear face being obscured, and the loss of its ‘L’ shaped plan form.

The proposed flat-roofed dormer would extend from the host’s ridgeline, almost to its eaves, and would cover virtually all of its roof slope. It would thus fail to accord with the advice at paragraph 4.10 of the [name] Planning Document 2017 (‘SPD’) that roof extensions should be secondary to the size of the roof face and should avoid the appearance of a large box.

Considered cumulatively with the single storey extension, the scheme would have a substantial scale, and the rear of the resultant property would essentially comprise a series of rectilinear blocks extending from ground floor level to the ridge. None of the original property’s form or style would remain visible.

Although many nearby properties have been extended, including some with large dormers and single storey rear projections resulting in the loss of their ‘L’ shaped footprint, the combined bulk, scale and form of the development here would be markedly at odds with the area’s prevailing character. That harmful impact would be apparent from the rear gardens and rear windows of many nearby properties.

Notwithstanding some tree cover, it would also be visible in the streetscene. In particular, as the proposed side extension would not be set in from the host’s side wall, and the proposed dormer would extend almost to the roof edge, the scheme’s rectilinear, unarticulated, bulky form would be seen through the gap between the host and [address]. In those views it would jar with the much simpler gabled profile at the end of many terraces in the IRCA. Given its size and proportions, the scheme’s impact would be materially more harmful compared to the previous permission.

Consequently, notwithstanding the proposed use of matching materials, the scheme would significantly harm the character and appearance of the host property and the area. It would therefore conflict with those parts of [name] CC1, CC2 and SC7 which require high quality design, that complements the original building, harmonises with adjoining properties, and responds to context and character, having regard to matters such as layout, grain, massing and the local architectural vernacular. It would also fail to accord with the advice in the SPD.

For similar reasons, the scheme would fail to preserve or enhance the character and appearance of the IRCA. In accordance with the National Planning Policy Framework (‘Framework’), I have attributed great weight to the conservation of that 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 the public benefits of the proposal.

There would be economic benefits as a result of employment opportunities for local builders and a potential rise in Council Tax receipts; as well as social benefits arising from the provision of additional family accommodation. However, notwithstanding the inclusion of energy efficient design features, given the harm that I have identified, the scheme would not comply with the Framework’s environmental objective.

The benefits would be relatively modest, particularly so in comparison with the previous permission. Therefore, I find no public benefits that would outweigh the harm that I have found, and the scheme would thus also fail to accord with HLP Policy CC4 and the Framework.

There were no objections to the proposal from interested parties. However, for the above reasons, having considered it on its planning merits, there are no material considerations that would outweigh the conflict with the development plan, and the appeal is therefore dismissed.