Appeal 6000721

The appeal is allowed and planning permission is granted for hip to gable extension incorporating rear dormer and alterations to existing dwelling at [site address] , Twickenham [postcode] in accordance with the terms of the application, Ref PA25/1868, subject to the following conditions:

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

The development hereby permitted shall be carried out in accordance with drawing nos: KTD.01; KTD.02; and KTD.03.

The external materials of the extension hereby permitted shall match those used in the existing dwelling and shall be retained as such thereafter.

The development hereby permitted shall be carried out in accordance with the provisions of the [name], prepared by Beta Town Planning Ltd, dated June 2025 and shall be retained as such thereafter.

Following the submission of the appeal, the [site address] Local Plan 2024-2039 (LP) was adopted in October 2025. The parties were given the opportunity to comment on the change in policy context, and I have taken these comments into consideration.

The main issue relevant to this appeal is the effect of the proposal on the character and appearance of the area.

The appeal property is a semi-detached bungalow with a tiled hipped roof. It has a wraparound addition featuring a crown roof. The adjoining property shares a similar design, as do several others in the surrounding area. Rear flat-roof dormer windows are a common characteristic locally and are generally visible due to the modest height of nearby dwellings and the pattern of development. [site address] (No 121) occupies a corner plot, making its side and rear elevations prominent from the street. The area is characterized by small-scale residential dwellings, similar in scale and design to the appeal property.

The proposal seeks permission for a hip-to-gable extension to the main roof, the installation of several rooflights on the front roof slope, and a dormer window on the rear roof slope. Based on the evidence provided, the Council previously issued a Certificate of Lawful Development (CLD) for a similar scheme which comprised a hip-to-gable extension, front rooflights, and a rear dormer window. The key differences between the current proposal and the CLD scheme relate to the number of front rooflights and the scale of the dormer window.

While the hip-to-gable extension would partially erode the symmetry of the attached properties, its modest scale would prevent any significant imbalance. Furthermore, there are several examples of similar semi-detached dwellings in the wider area that have undergone hip-to-gable extensions. Within this context, the proposed design would not appear out of character. The limited size and positioning of the front rooflights would ensure they would not create a cluttered appearance on the front roof slope.

The [site address] [name] and Alterations Supplementary Planning Document (SPD) states that roof extensions should not dominate the original roof. Normally a significant area of the existing roof should be left beneath a new dormer and on either side of the dormer, thus setting the extension well in from either side of the roof.

The proposed dormer would retain considerable space above and below, aligning with SPD guidance. However, when considered against the original roof, the dormer would leave limited space on either side. That said, the SPD refers to the original roof, whereas in this case, the proposal would include a substantial addition to the roof. Viewed in this context, the dormer would maintain adequate spacing on all sides and would not dominate the extended roof. The use of hanging tiles would complement the existing roof materials, helping the dormer window to integrate visually.

Although the proposal does not fully accord with SPD, the document serves as guidance rather than policy. As the dormer window would not dominate the extended roof it would generally accord with the purposes of the guidance in the SPD on this matter. The modest scale and design of the proposal would appear as a proportionate addition to the dwelling and would be sympathetic. This would preserve the dwellings overall scale and appearance relative to the neighbouring property and others nearby. As such, the scheme would not unbalance the semi-detached pair, and the design and use of matching materials would contribute to ensuring the extended dwelling would remain in keeping with the character of the area.

Therefore, the proposed development would not harm the character or appearance of the area. Consequently, the development would comply with Policy 28 of the LP. This seeks, amongst other matters, for development to ensure the proposal is compatible with the local character and provides a high-quality sustainable design.

Further to the statutory commencement condition, a condition requiring the development to be carried out in accordance with the permitted plans is necessary in the interests of certainty. A condition requiring the materials used match those in the existing dwelling is necessary in the interests of the character and appearance of the area. Condition 4 requiring the development is carried out in accordance with the [name] is necessary in the interests of fire safety in accordance with Policy D12 of the London Plan.

The proposed development would comply with the development plan, and the material considerations do not indicate that the appeal should be determined other than in accordance with it. Therefore, for the reasons given above, I conclude that the appeal should be allowed.