Appeal 3262670

The appeal is dismissed.

An application for costs has been made by [name] against the Council of the London Borough of Merton. That application is the subject of a separate decision.

Following the determination of the planning application, the Mayor of London published a new Plan, The London Plan (March 2021) (LP). The Government also published the National Planning Policy Framework 2021 (the Framework). I have sought comments from the main parties with regard to these matters and have taken their responses, where these have been provided, into account in making my decision.

The appellant provided additional information with the appeal which did not form part of the application before the Council. The Council and third parties have been given the opportunity to comment on this information and I have taken the responses received into account when determining the appeal.

As part of the aforementioned additional information, the appellant provided a revised drawing showing that the front boundary wall of the appeal site was to remain unchanged. As such, the second refusal reason falls away and there is no need for me to consider it further.

The main issues are the effect of the proposal on: • the character and appearance of the locally listed host building and the Wimbledon West Conservation Area; and, • drainage and flood risk in the area.

The appeal site is located in the Wimbledon West Conservation Area (CA). Section 72(1) of the Planning (Listed Building and Conservation Areas) Act 1990 requires that, in making decisions on planning applications and appeals within a Conservation Area, special attention is paid to the desirability of preserving or enhancing the character or appearance of the area.

The CA derives its significance, in part, from the quality of its buildings and its spacious and verdant character. [site address] consists of a number of large, detached dwellings that sit within plots of similar depths but with varying widths. The host building dates from around 1890 and is locally listed. It is a large building constructed in yellow [name] brick under a tiled roof with attractive red brick detailing and has previously been extended to the side and rear. It has a large garden with a significant gap to the adjacent dwelling at No.25 [site address] , which provides a pleasant sense of openness in the streetscene. The immediate space around the host dwelling, consisting of its gardens, as well as its relationship to other buildings within the streetscene, contribute to its setting.

The proposal includes numerous elements, including extensions to the host building and the remodelling of a single storey rear extension granted consent under extant planning permission 20/P0627. The Council do not raise any objections in relation to these elements and having assessed the proposal I see no reason to reach a different conclusion. The point of contention between the main parties is the provision of a basement extension.

Policy DM D2 of the Sites and Policies Plan and [name] (July 2014) (SPP) sets out a number of criteria relating to basement development. This states, amongst other things, that basements should not exceed 50% of either the front, rear or side garden of the property and result in the unaffected garden being a usable single area. The Council calculate that the proposed basement would exceed more than 50% of the front, side and rear gardens. The appellant calculates that the proposed basement would cover 39.1% of the side garden, 38.8% of the rear garden and 24.3% of the front garden.

The appellant has provided drawing P14 to show how they have calculated the area of the basement. This illustrates that the proposed basement would not exceed more than 50% of the front and side gardens. However, to the rear, the basement would also be located beneath the proposed rear extensions. As these extensions have not yet been constructed, and it cannot be guaranteed with complete certainty they would be, I consider that that any assessment should be based on the current circumstances on site. Therefore, I consider that the space the extensions would occupy must be considered garden for the purposes of calculating whether the proposed basement would exceed 50% of its area. When this area is included, it is clear from drawing P14 that the basement would cover more than 50% of the rear garden.

I acknowledge that the Council’s approach to considering such development has been inconsistent in terms of the method of calculation for basement areas. In this regard, I note the planning permission granted in respect of 49 Murray Road1. At paragraph 7.9 of the Council’s Officer Report for that application, it is evident that the Council calculated the area of the proposed basement by measuring the garden area from beyond the proposed ground floor rear building line. While the Council’s inconsistent approach is unfortunate, I consider that it is more logical to assess the appeal proposal using calculations based on the current site conditions for the reasons explained in the previous paragraph.

That the proposed basement would exceed more than 50% of the rear garden is indicative that it is of an excessive size and would be out of scale with the host site and locally listed host building. Although the basement would not be visible above ground, it would, by virtue of its excessive size, nevertheless result in a disproportionate addition to the host building and would fail to respect its original design and form. Consequently, I consider that the proposed basement would harm the character of this locally listed building.

I note the Council’s Conservation Officer concerns that the proposed basement may have on the safety of the host building. However, I consider that this matter could be addressed by way of an appropriately worded condition to ensure its structural integrity. Such a condition could require full details of the methods to be used in the construction of the basement and how the host building would be protected throughout.

I also note that the Council are concerned that the proposed basement would have a harmful effect on the setting of the locally listed host building. The appellant has submitted a section drawing that shows that one metre depth of soil would be retained above the basement. This would be sufficient to ensure that the retained garden areas could be landscaped. Moreover, as the basement would not be visible once constructed it would have no impact on the existing sense of openness that contributes to the setting of the host building. However, the absence of harm in respect of this matter is a neutral factor in my overall considerations. It does not diminish the harm that the proposed basement would cause to the character of the host dwelling.

In applying the balanced judgement set out at Paragraph 203 of the Framework, I consider that the harm that would be caused to the locally listed host building would be considerable. No public benefits have been suggested by the appellant that may outweigh that harm.

With regards to the effect of the proposal on the CA, the proposed basement would not be visible once constructed, from either the public realm or from neighbouring properties. Further, the Council has no objection to the proposed lightwells to the rear of the dwelling or the steps down to the basement. Given their location, scale and design, I see no reason to reach a different conclusion. The proposed basement extension therefore would have a neutral effect on the character and appearance of the CA which would be preserved. 1 17/P2820.

I conclude that the proposal would cause harm to the character of the locally listed host building. There would be conflict with [name] D2, DM D3 and DM D4 and Policy CS 14 of the London Borough of Merton LDF Core Planning Strategy (July 2011). These require, amongst other things, that development conserves or enhances Merton’s Heritage assets, that extensions respect the scale of the original building and that basements do not exceed 50% of either the front, rear or side gardens. The proposal would also conflict with [name] D3, D10 and HC1 in as far as they relate to ensuring good, high quality design, basement development and the effect of development on heritage assets. It would also conflict with the aims of conserving and enhancing the historic environment set out in the Framework.

The appeal site is located in [name] 1 and the appellant provided a [name] (SWDSR) with the application. This indicates that a [name] (SUDS) scheme would be incorporated into the proposal. Under that scheme, surface water run-off would be discharged into the existing public surface water sewer in [site address] , but at a restricted rate using a vortex flow control and surface water storage provided in an underground cellular attenuation tank. In addition, rainwater harvesting for garden use is proposed and infiltration drainage is viable for the car parking area using permeable paving.

I am satisfied that the proposed SUDS scheme would deal adequately with surface water and prevent increased risk of flooding in the area. Moreover, the SWDSR includes a management and maintenance plan to ensure that the SUDS scheme would be maintained throughout the life of the development. Both the SUDS scheme and its on-going maintenance could have been secured by condition if, in the event, the appeal had been allowed.

The Council also consider that the proposal should show how the basement would remain dry throughout the life of the development. If the appeal had been allowed, I am satisfied that details to adequately address this matter could have been secured by condition.

I note that local residents have raised concerns with regards to the effect of the proposal on nearby underwater streams, the water table, ground water flow around no [address] and existing flooding of basements at properties on [address]. However, I do not have any further information to substantiate these concerns. As such, this does not alter my conclusion on the acceptability of the proposal in terms of drainage and flood risk for the area.

I conclude that the proposal would not cause harm to the drainage and flood risk for the area. It would comply with [name] D2, DM F2 and CS Policy CS 16. In summary, these seek, among other matters, to ensure that development proposals do not result in flooding and that they reduce the borough’s susceptibility to surface water flooding. It would also accord with [name] 12 and SI 13. These require, among other matters, that development proposals ensure that flood risk is minimised and mitigated and that they should aim to achieve greenfield run-off rates. The proposal would also accord with the overarching aims of the Framework.

I have found that, despite the Council’s concerns, the proposal would provide for an appropriate SUDS scheme which would be maintained thereafter and which would ensure that no harm would be caused to the drainage and flood risk in the area. However, this is significantly outweighed by my conclusion that the proposal would cause harm to the character of the locally listed host building. I have found that such harm would be considerable and that there are no public benefits that would result to mitigate such harm.

For the above reasons, having considered the development plan as a whole, the approach in the Framework, and all other relevant material considerations, I conclude that the appeal should be dismissed.