Appeal 3333506

The appeal is allowed and planning permission is granted for a single storey rear extension accommodating a swimming pool, together with raising of roof by 1.2m, front entrance porch, alterations to fenestrations involving replacement windows and doors at [site address] , Enfield in accordance with the terms of the application, Ref 23/02028/HOU, dated 23 June 2023, subject to the following conditions:

The development hereby permitted shall be begun before the expiration of three years from the date of this decision.

The development hereby permitted shall be carried out in accordance with the following approved plans: 01252 P A01 [name], 01252 [name] A01 [name], 01252 [name] A02 [name], 01252 [name] A03 [name], 01252 [name] A04 [name], 01252 [name] A05 [name], 01252 [name] A06 [name], 01252 [name] A07 [name], 01252 [name] A08 [name], 01252 [name] A09 [name], 01252 [name] A10 [name], 01252 [name] A11 [name], 01252 [name] B01 [name], 01252 [name] B02 [name], 01252 [name] B03 [name] and 01252 [name] B04 [name].

Prior to works commencing on the swimming pool element of the proposal and notwithstanding the detail of drawing 01252-P-SW-A12 [name] which is not approved, a cross-section showing the depth of the swimming pool and details of the construction method and flood risk mitigation measures shall be submitted to and agreed in writing by the local planning authority. The plans shall be supported by groundwater level monitoring and assessments. The works shall be carried out in strict compliance with the approved plans and measures. www.planningportal.gov.uk/planninginspectorate Appeal Decision: APP/Q5300/D/23/3333506

The main issue is whether the proposal would be safe from flooding; and would not increase the risk of flooding elsewhere.

The application was amended during the period of the council’s consideration. It is evident that the revised plans were taken into account as they are listed in the decision notice. The original description did not make reference to the swimming pool. The appellant suggests that the description of development should be amended to read ‘Single storey rear extension accommodating a swimming pool, together with raising of roof by 1.2m, front entrance porch, alterations to fenestrations involving replacement windows and doors’. The decision notice includes the same description except it adds reference to the creation of an integral garage. I am satisfied that the appellant’s description adequately describes the proposal and have adopted this wording.

The council’s concerns relate only to the issue of flood risk. Other concerns have been raised by third parties but other than the swimming pool addition and some minor alterations, the proposal follows a similar approved application that accepted the increased scale, height and details now proposed again. As the previous approval represents a clear fallback position that is in the process of being implemented, the other matters are effectively settled. The general form and extent of the swimming pool building has also been previously approved, within the period of the majority of the development plan policies. In any event, the structure itself or the activity associated with it, would not result in any increase in harm to neighbouring amenity. As it is to the rear, it would not alter the appearance of the property or its perceived scale. Given the above, the following relates only to the matters arising with regard to flood risk in relation to the additional works required in relation to the swimming pool.

The only plan that demonstrates the depth of the swimming pool is drawing 01252-P-SW-A12 [name]. This appears to show a construction depth of 2.4m below the ground floor datum level of 98.92m. The supporting documents suggest that the maximum construction depth of the swimming pool would be 2.585m. In response to the council’s reason for refusal, the appellant carried out ground water monitoring at three points, two of which, WS1 and WS2, are in the rear garden area. The highest ground water levels at WS1 are recorded as 2.74m whilst at WS2 it was 2m.

The appellant advises that the WS2 borehole, which lies below the proposed swimming pool, to the south, is on a grassed area and due to [name] and [name], the surface water would have accumulated in the sand layer that lays above the clay layer of ground. The water was therefore considered to be perched water caused by the storms, rather than it being the actual groundwater level. The standing groundwater level at WS1, which is located further into the garden and to the west of the swimming pool was recorded as 2.74m below ground level. As WS1 is closer to the works, the appellant is of the view that the proposed swimming pool dig level would be above the 2.74 level and in any event, would not impede any flood flow routes as the high groundwater level is caused by an accumulation of surface water resulting from the two storms mentioned above rather than a high water table. 2 Appeal Decision: APP/Q5300/D/23/3333506

It is suggested that the developer would be aware of this matter and that pumping could take place during the construction and build stage if necessary. In addition, it is proposed that resilience and mitigation measures would be provided in the form of ensuring that the structures are designed to resist any potential hydrostatic uplift forces which may be imparted by the presence of perched groundwater; and the swimming pool would be designed as a watertight element and a waterproof membrane would be included to address the potential for the soils at foundation depth to deteriorate rapidly in the prolonged presence of water. It is suggested that it may also be prudent to apply a blinding layer of lean-mix concrete to all excavations, if continuous working cannot be achieved.

Given the nature of this appeal procedure, the council has not had the opportunity to comment on the new information submitted by the appellant. I am unable therefore, without prejudicing the council, to accept this new evidence without reverting to the parties. Whilst this procedure does not facilitate this, the swimming pool building itself does not represent a concern with regard to flood risk and has been approved previously in this general form. It is only the depth of development to accommodate a below ground swimming pool that is the issue. Setting aside the cross-section plan, drawing 01252-P-SW-A12 [name], showing the depth of development, the proposal for these works would be acceptable. The only issue is therefore the depth of the swimming pool.

It is not essential for such a pool to be below ground or entirely below ground. It is reasonable, in these circumstances, to impose a condition requiring, notwithstanding the cross-section proposed in drawing 01252-P-SW-A12 [name] which is not approved, that the depth of the below ground works, together with the proposed construction methods and mitigation details, be submitted to and agreed by the local planning authority. This would allow for the council to consider the submissions already made and any more up-to-date monitoring results, outside the periods of the two storms. Whilst the current depth may be considered appropriate based on the information submitted, it would also allow for flexibility with regard to the extent of the below ground depth of the swimming pool which would be agreed between the parties without constraining the completion of the other elements of the development. This approach would be consistent with the development plan and National Planning Policy Framework objectives of ensuring that development would be appropriately flood resistant and resilient and would not result in increased flood risk elsewhere. Subject to such a condition, the development would be acceptable. I therefore allow the appeal.

In addition to the above described condition, I have imposed additional conditions relating to the commencement of development and the details of the approved plans for the avoidance of doubt and in the interests of proper planning. The details of the materials are clearly illustrated on the approved plans.