Appeal 3353128

The appellant’s description of the proposed development is set out above. However, the Council described the appeal proposal as: ‘erection of a single storey side and rear extension and a rear roof extension with hip to gable conversion with front roof windows to the house’. As this description more comprehensively details the proposed works, it has been used in this decision.

As the two elements of the appeal proposal are severable and could be carried out independently of each other, I have determined the appeal on this basis.

The appeal is dismissed insofar as it relates to the single storey side and rear extension. The appeal is allowed insofar as it relates to a rear roof extension with hip to gable conversion with front roof windows to the house, and planning permission is granted for a rear roof extension with hip to gable conversion with front roof windows to the house at [site address] , Hounslow [postcode] in accordance with the terms of the application, [name]/2024/1845, so far as relevant to that part of the development hereby permitted and subject to the following conditions:

The development hereby permitted shall begin not later than 3 years from the date of this decision.

The materials to be used in the construction of the external surfaces of the development hereby permitted shall match those used in the existing building.

The development hereby permitted shall be carried out in accordance with the following approved plans, so far as relevant to that part of the development hereby permitted: Location Plan, HS/3021/01, HS/3021/02, HS/3021/03, HS/3021/04, HS/3021/05 and HS/3021/06 and the [name].

The main issues in this appeal are the effect of the appeal proposal on the living conditions of the adjoining occupiers at No [address] (No 22), in terms of loss of light, outlook and sense of enclosure and its effect on the character and appearance of the host property and the surrounding area, including whether it would preserve or enhance the character or appearance of the Osterley Park Conservation Area (the Conservation Area), and its effect on the significance of the designated heritage asset.

The proposed single storey rear extension would run along the party boundary with No 22 at a depth of 4.5m and a height of 3m. In my judgement, this depth of development along the boundary would result in a loss of outlook for the neighbouring occupiers and it would also create a sense of enclosure due to its overbearing effect. Having regard to the orientation of the two properties, I am satisfied that there would be no loss of daylight and sunlight but this does not overcome the identified harm.

Furthermore, the depth of the extension would conflict with the Council’s guidance set out in the [name] (the SPD). This indicates that single storey rear extensions on semi-detached properties should not exceed 3.65 metres in order to protect the living conditions of neighbouring occupiers. [name] recognise the appellant’s needs to extend the property to provide more living space for the family, alternative designs could provide the necessary space without compromising neighbouring amenities.

I conclude that the extension would harm the living conditions of the neighbouring occupiers in terms of loss of outlook and the creation of a sense of enclosure. Accordingly, the single-storey extension element of the appeal proposal is contrary to Local Plan Policies CC2 ([name] and Architecture) and SC7 ([name] and Alterations) and would conflict with the design guidance in the SPD.

In accordance with the statutory duty, it is necessary to determine whether the appeal proposal would preserve or enhance the character or appearance of the Conservation Area. The appeal property is a semi-detached house set on a wedge-shaped plot towards the head of a cul-de-sac containing similar properties. The Osterley Park Conservation Area Appraisal (the Appraisal) indicates that the appeal site is in the [address] and [address] character area. This comprises an estate of late interwar and early postwar two storey semi-detached houses with some short terraces on and off [address]. To the rear of the estate is a recreation ground.

The Appraisal refers to the ongoing demand for the refurbishment and renovation of existing buildings, some of which are positive contributors to the Conservation Area. It identifies negative features which have impacted on the quality of the historic environment, stating that in areas outside Osterley Park the scale of proposed development, particularly extensions and alterations to rooflines, can affect vistas and settings. The Appraisal indicates that detailed advice on residential extensions is provided by the SPD.

The Council has not provided an overview of the defining conservation characteristics of the appeal site nor identified its contribution to the character or appearance of the Conservation Area as a whole. Based on the evidence with this appeal together with my observations at the site visit, I consider that the preservation of the semi-detached suburban character of the property within its surroundings of similar houses is of most relevance to this appeal. When it is considered alone, the appeal property makes a neutral contribution to the character, appearance and significance of the Conservation Area.

As discussed above, the single-storey rear extension element of the proposal would project 4.5 metres beyond the rear elevation of the original house. It would not respect the scale and proportions of the host dwelling and it would not be sufficiently subservient. Notwithstanding that in itself the side extension element would be proportionate and subordinate to the dimensions of the host property, I conclude that the extension would harm its character and appearance. Due to its shielded location at the rear of the dwelling, the character and appearance of the Conservation Area would be preserved.

Turning to the roof alterations, the SPD indicates that extending a hipped roof to form a gable end on a side roof would normally be refused planning permission where it would unbalance the appearance of a pair of semi-detached houses. Nos 21 and 22 are a pair of such properties of identical design and the appeal proposal would unbalance them. However, as the road contains a mix of roof styles, particularly in the area around the appeal site, the requirement for symmetry is less compelling than it might be elsewhere. Moreover, the orientation of the pair of semi-detached houses and the spatial relationship of the appeal property with the road and the adjacent No 20 due to the wedge shape of its plot would further minimise any visual impact of the side roof extension.

Overall, the proposed roof extension would be proportionate to the scale of the host dwelling and would not appear as a bulky or incongruous addition. In my judgement the proposed change in roof profile would not appear out of keeping with the suburban character and appearance of an area where a number of similar alterations have been carried out. Notwithstanding that they may predate the adoption of the SPD, these extended houses are part of the established visual context of the appeal site. Furthermore, the proposal would have no adverse effect on the vistas and settings which are important to the character of the Conservation Area.

In accordance with the SPD standards for dormers on semi-detached properties, the proposed rear dormer would be above the eaves and set in from the sides of the roof, notwithstanding the hip to gable roof extension. As discussed above, there are existing rear and side dormers close to the appeal site, as well as front rooflights. Within this context the dormer and roof lights are acceptable.

In conclusion, the proposed hip to gable extension would be sympathetic in design and proportion to the host dwelling, preserving its semi-detached suburban character. It would not appear out of character in its surroundings and would therefore preserve the character and appearance of the Conservation Area. It would not harm the significance of the designated heritage asset. Accordingly, the roof alterations would not be contrary to Local Plan Policies CC1 (Context and Character), CC2, CC4 (Heritage) and SC7 or the design aspirations of the SPD.

For the reasons set out above and having regard to all other matters raised, the appeal is dismissed in respect of the single-storey rear and side extension and allowed in respect of the loft conversion works.

External materials to match are required by condition to safeguard visual amenities. I have included a condition which identifies the approved drawings for the avoidance of doubt and in the interests of proper planning.