Appeal 3344676

The appeal is Dismissed.

There are a few discrepancies between the submitted drawings and the form and appearance of the appeal dwelling at the time of the appeal site visit. In particular, the dwelling has had a hip to gable roof extension, rear dormer extension and a single storey flat roofed addition located at the side of the dwelling. For the avoidance of any doubt this decision needs to be determined on the basis of the submitted drawings, upon which the council based its decision. This is because any material variations would first need to be formally considered by the local planning authority and subject to any necessary associated consultations.

The main issue is the effect of the proposal on the risk of flooding within the functional floodplain in the locality.

The appeal property is situated within an established residential area, where it is located in a prominent position adjacent to the junction of Crossway and [address]. The property comprises an attached two storey family dwelling, which occupies a comparatively wide plot. The proposed two storey extension would be constructed at the side of the original dwelling and would have a footprint of some 38m2.

With regard to the form and design of the proposed extension, I am satisfied that it would respect the character and appearance of the host dwelling and the street scene as a whole. Also having regard to the distance and juxtaposition between the proposed extension and nearby dwellings it would not have an unacceptable impact on the outlook from or light within nearby dwellings.

The appeal site is located within the Environment Agency’s (EA), [name] 3 and the council’s drainage engineer has stated that the site is partially within the functional floodplain. The appeal site is shown on the EA’s web site surface water flood risk map as being at medium risk from surface water flooding and the EA has also produced a plan which shows that the site flooded in 1968. The appellant’s Flood Risk Assessment (FRA), states that as the proposal does not include a basement the risk from ground water flooding is low.

Paragraph 165 of the National Planning Policy Framework 2023 (the Framework) states that inappropriate development in areas at risk of flooding should be avoided by directly development away from areas at highest risk. Where development is necessary in such areas, it should be made safe for its lifetime without increasing flood risk elsewhere. In accordance with Paragraph 174 and footnotes 59 & 60 of the Framework a full flood risk assessment for the proposal is required although sequential and exceptions tests are not.

Paragraph 173 of the Framework states that development should only be allowed in areas at risk of flooding where, in the light of the flood risk assessment it can be demonstrated that: A) within the site, the most vulnerable development is located in areas of lowest flood risk, unless there are overriding reasons to prefer a different location; b) the development is appropriately flood resistant and resilient such that, in the event of a flood, it could be quickly brought back into use without significant refurbishment; c) it incorporates sustainable drainage systems, unless there is clear evidence that this would be inappropriate; d) any residual risk can be safely managed; and e) safe access and escape routes are included where appropriate, as part of an agreed emergency plan.

Together and amongst other things policies DM F1 and DM F2 of the Merton Local Plan’s Sites and Policies Plan 2021 (DMP) and policy CS16 of Merton’s Local Development Framework Core Planning Strategy (MCS), seek to manage and reduce flood risk from all sources of flooding. To require the implementation of sustainable drainage systems in new developments and across the borough; and to implement flood risk measures across the borough to ensure that any residual risk can be safely managed. Flood resilience and resistance measures should be incorporated into the design of development proposals.

The EA provides standing advice on flood risk for planning applications for minor extensions. Amongst other things it advises that FRA’s should include the estimated flood levels that could affect the development, taking account of climate change over its lifetime; details of finished floor levels; and details of flood resilience and resistance plans.

The standing advice also states that plans need to show how the development would be kept free from flooding. For minor extensions it recommends that floor levels are at least 600mm above the estimated flood level. This can be reduced to 300mm if there is a high level of certainty re flood levels, although where there is uncertainty it should be increased. Flood resistant materials should be used up to at least 600mmm above the estimated flood level. Where these floor levels can be achieved extra flood and resilience measures will be required to protect the property to at least 600mm.

The appellants FRA refers to the [name] Study completed in2008, which show flood risk levels close to the appeal property at 16.10 AOD, which equates to 1% chance of flooding. It is noted that this data does not take into account the current Climate change allowances set out in the Framework.

The appellant’s FRA states that the internal floor level would match that of the host dwelling, however, no site or floor levels have been provided. Without such information it is not possible to compare the site levels with the modelled flood level or whether any part of the proposed extension would fall within the functional floodplain. The proposal’s impact on potential surface water flooding both on and around the appeal site is not known. Similarly, it has not been demonstrated that the proposed extension could be made safe for the life of the development.

The appellant’s FRA does refer to possible surface water drainage measures and the drawings show at rainwater attenuation tank, along with measures to make the extension resistant and resilient to flooding. However, there is no certainty that such measures would all be appropriate or fully effective. The proposal would therefore conflict with the social and environmental objectives of sustainable development, as set out in the Framework.

The above concerns relating to flood risk clearly outweigh the acceptability of the proposal in relation to visual impact design and the benefits for the appellant and their family that would result from the additional living accommodation. Due to the absence of necessary information and the uncertainty regarding the impact of the proposal on flood risk this is not a matter that could be satisfactorily dealt with by condition.

For these reasons I conclude on the main issue that it has not been demonstrated that the proposal would have an acceptable impact on the risk of flooding within the functional floodplain in the locality. Accordingly, the proposal conflicts with [name] DMF1 & DMF2, MCS Policy CS16, Paragraph 173 of the Framework and the [name].