Appeal 3375487

The appeal is dismissed.

The main issues are the effect of the proposed development on: • the character and appearance of the area; and • flood risk.

The appeal site is a semi-detached bungalow occupying a prominent corner plot within a residential area characterised predominantly by bungalows. At the time of my visit, the property had already been altered through a hip‐to‐gable roof extension and rear dormer window, altering the original hipped‐roof form shown on the submitted existing plans.

The proposed development would introduce a wraparound single‐storey extension extending the full depth of the side boundary and across the rear elevation, broken only by a small courtyard gap to the side elevation. In practice, it would read as a largely continuous addition enveloping two sides of the bungalow.

At my visit, I observed the existing flat‐roofed rear extension with a tall parapet. Whilst visible from the street, that structure is confined to the rear and set away from boundaries, thus limiting its visual effect on the wider streetscape. I also noted some examples of side and rear extensions on other corner plots in the area, which generally retain separation to the site boundaries and a subservience to the main dwelling, thereby preserving the established rhythm and spaciousness of the street scene.

Policy CS1 of the [name], February 2012 (the CS) and Policy DM1 of the Harrow Council Development Management Policies, July 2013 (the DMP) collectively require high‐quality design that responds positively to the local context and respects local character. The Residential Design Guide Supplementary Planning Document (the SPD) advises that corner sites are particularly sensitive, and that side extensions have considerable potential to cause harm if they erode the characteristic openness of such plots. Among other objectives, the SPD requires development proposals to consider the pattern of development, local character, and the need for extensions to remain subordinate to the host building.

In this case, the flat roof of the proposed extension would project above the bungalow’s original eaves line and would extend directly to the side boundary in a highly prominent position. Combined with the wraparound form, this would substantially increase the perceived bulk of the dwelling when viewed from the public realm. The result would be an overly dominant and incongruous addition, at odds with the modest scale of the host bungalow and the openness that characterises corner plots in the area. The proposal would therefore disrupt the established pattern of development, appearing uncharacteristic and visually intrusive.

I note the appellant’s references to matching materials, the presence of other extensions in the locality including the use of flat roofs, and the courtyard break in the built form. However, the development must be assessed on its own merits, and these factors do not overcome the fundamental concern that the proposal’s height, boundary siting and overall bulk and massing would erode the open character of the corner plot and would fail to read as a subordinate addition.

Accordingly, I conclude that the proposed development would harm the character and appearance of the area and would conflict with Policy CS1 of the CS and Policy DM1 of the DMP, as well as the provisions of the SPD, the aims of which have previously been set out. It would also conflict with the relevant provisions of the National Planning Policy Framework (the Framework), which have similar aims.

A Flood Risk Assessment (FRA) accompanied the planning application. This states that whilst part of the appeal site lies within [name] 2 on the Environment Agency’s Flood Map for Planning, the footprint of the dwelling and the proposed extension are within [name] 1. Even so, the FRA acknowledges that parts of the site are subject to both fluvial and surface‐water flood risk, and that the site also lies within a Critical Drainage Area.

In such circumstances, Policies DM9 and DM10 of the DMP require proposals to demonstrate that development will be resistant and resilient to all relevant sources of flooding, will not increase flood risk elsewhere, and will make adequate provision for the management, control and reduction of surface‐water run‐off. Policy DM9 requires evidence that development minimises the risk of flooding on site and does not increase the risk of flooding elsewhere, with appropriate mitigation and measures to manage floodwater movement and storage. Policy CS1 of the CS similarly seeks to manage development to achieve an overall reduction in flood risk and to increase resilience to flood events across the Borough. Policy SI 12 of the London Plan, March 2021 (the LP) reinforces these objectives by requiring that development proposals ensure flood risk is minimised and mitigated, and that residual risk is addressed.

The FRA asserts that any displaced floodwater would be contained within the plot. However, it also confirms that no site‐specific topographic survey was undertaken. The statements regarding existing ground levels, including that a natural depression in the rear garden would be capable of providing compensatory flood storage, are unsupported by measured data, surveyed levels, or any volumetric

From the evidence before me, I am provided with no reliable indication that the curtilage could accommodate the displaced volume of water identified by the FRA. In the absence of quantified modelling or other substantive evidence demonstrating that floodwater could be safely stored on site, the proposal fails to demonstrate that it would satisfy the development plan requirements for managing the displacement of floodwaters and providing suitable compensatory flood storage.

The appellant contends that outstanding matters could be resolved through the imposition of conditions requiring the submission of further details. However, the information before me provides insufficient reliable evidence that the site could accommodate the necessary compensatory flood storage in principle, nor that any necessary engineering solution would be deliverable within the physical constraints of the plot. In these circumstances, the absence of detail prevents me from confidently concluding that an acceptable solution is realistically achievable. A condition cannot be used to defer consideration of a matter that goes to the principle of whether the development can be made safe without increasing flood risk elsewhere, nor is it appropriate where there remains a risk that the required mitigation may ultimately be undeliverable.

Accordingly, I conclude that the proposed development fails to demonstrate that it would not result in the displacement of flood waters, and it has not been demonstrated that suitable compensatory flood storage could be provided on site. The development would therefore have an unacceptable impact in terms of flood risk, and would conflict with [name] DM9 and DM10, CS Policy CS1, and LP Policy SI 12, the aims of which have previously been set out. It would also conflict with the relevant provisions of the Framework, which have similar aims.

For the reasons given above, I conclude that the appeal should be dismissed.