Appeal 3369860

The appeal is dismissed.

The site visit was undertaken by a representative of the Inspector whose recommendation is set out below and to which the Inspector has had regard before deciding the appeal.

The Council has raised no concern with the proposed rear extension. On the evidence before me, I see no reason to disagree.

Therefore, the main issue is the effect of the proposed loft conversion on the character and appearance of the host dwelling and surrounding area, including whether it would preserve or enhance the character or appearance of the Osterley Park Conservation Area (CA).

Having regard to the Osterley Park Conservation Area Appraisal (CAA), the CA comprises the park itself, late nineteenth century railway-related development and some twentieth century interwar development. The significance of the CA as a heritage asset is derived in part from this history, and from the suburban houses built around the railway, which reflect the character of their time. This includes the integrity of the houses’ roofs and architectural features.

The CAA places the appeal site within Character Area 3: [address], which is specifically recognised for its suburban housing reflecting the expansion of the railway suburbs. [address] is generally made up of semi-detached and terraced dwellings. Whilst there is variation in style along the road, there are clear groups of established, uniform dwellings.

The appeal dwelling is a two-storey, semi-detached property and forms part of a largely symmetrical pair and a group of similar dwellings at the northeastern end of [address]. Although many of these properties have been extended over time, these alterations are predominantly subservient to the host buildings, so much of the original roofscape can still be discerned. As a result, there is prevailing regularity in the appearance of the dwellings. This consistency, including respect for original roof forms, contributes positively to the character and appearance of the local area and the significance of the CA.

The Hounslow Character, Sustainability and Design Codes Supplementary Planning Document Residential Extensions Guidance (REGs) sets out that roof extensions should be subservient to the size of the roof in which they are set. It also resists roof extensions that would unbalance the appearance of a semi-detached pair and restricts large roof extensions in conservation areas where they would harm the character of the area.

To accommodate the loft conversion, the development would introduce a substantial new hipped roof element between the existing and proposed new gables. The ridgeline of this new element would be only marginally below the apex of the principal front-facing gable. The resulting new roof mass would be dominant rather than subservient to the existing roof, notwithstanding the proposed use of matching materials, and would be fundamentally different in form to the roof of the adjoining house. Consequently, as well as conflicting with the REGs guidance, the proposal would erode the balance of the semi-detached pair and the appeal dwelling’s contribution to the integrity of the original roofscape in the area. This would in turn fail to preserve the character or appearance of the CA and thereby harm the significance of the designated heritage asset.

I recognise that the planning permission for a loft conversion at [address] (Ref 00700/29/P4) is similar in a number of respects to the appeal proposal. However, from the plans before me, the new roof approved at No 29 is materially lower than and clearly set down from the existing ridge height, such that it appears subservient to the main roof. This helps maintain the integrity of the original roof form in that case. By contrast, the new roof in the appeal scheme is not subservient for the reasons given above. Furthermore, I understand the permission at No 29 predates the inclusion of [address] within the CA. Together, these factors reduce the weight I give to No 29 as a precedent.

The appellant has drawn my attention to other examples of roof alterations in the area. The houses at 15 and [address] differ in their design to the typology of the appeal dwelling and the prevailing design of dwellings within the immediate context of the appeal site. In any event, the roof extensions to these properties mean that they appear generally uniform. As regards the alterations to dwellings on the northwestern side of [address], these are of a smaller scale and extent than the proposal before me. I also do not have full details of the policy context in which these other extensions were allowed, including whether the road was within the CA at the time. For these reasons, these other examples are not directly comparable and also do not outweigh the harm I have found.

The National Planning Policy Framework (2024) (the Framework) sets out that when considering the impact of development on the significance of a designated heritage asset, great weight should be given to the asset’s conservation, irrespective of the level of harm to its significance. In this instance, the level of harm would be towards the lower end of less than substantial. Where this type of harm arises, the Framework requires the harm to be weighed against the public benefits of the development.

The development would provide economic benefit during its construction by way of employment opportunity. There would also be an improvement to the energy efficiency of the house. However, given the modest scale of the proposal, I give these public benefits only limited weight. This is not sufficient to outweigh the great weight of the harm identified.

For these reasons, I conclude that the proposed loft conversion would have a harmful effect on the character and appearance of the host dwelling and surrounding area, and would thereby fail to preserve the character or appearance of the CA. This is contrary to Policies CC1, CC2, CC4, and SC7 of the Hounslow Local Plan 2015-2030 Volume 1. [name], among other things, aim to ensure development conserves and enhances the character of an area by responding sensitively to the local architectural vernacular, complementing the original building, and taking opportunities to enhance any heritage asset.

I have considered the planning permission at No 21 ([name]/2024/1819) and recognise this could be implemented in the event that this appeal fails. However, although it would also unbalance the semi-detached pair to a degree, that scheme would be a less harmful intervention than the proposed development. This is because it would comprise a more subservient side dormer and the original roof form and roofscape would retain greater legibility. For these reasons, I attach only limited weight to that permission as a fallback position, which is not sufficient to outweigh the harm I have found.

[name] note the appellant’s wish for an enlarged home, little weight can be attached to such personal circumstances. I recognise the Framework supports the upward extension of residential properties, but this is primarily in the context of creating space for additional homes rather than enlarging existing ones. In any event, such support is dependent on good design and consistency with the overall street scene, which I have not found to be the case in this appeal.

For the reasons given above and having had regard to all other matters raised, I recommend that the appeal should be dismissed. Finlay Bradford APPEAL PLANNING OFFICER

I have considered all the submitted evidence and my representative’s report and on that basis the appeal is dismissed. [planning inspector] INSPECTOR