43 Kenton Gardens
The Brief
RIDA Reports Ltd was appointed to undertake a Level 1 Flood Risk Assessment for a proposed residential development at 43 Kenton Gardens, Harrow (HA3 8DE). The project involves the construction of a single-storey rear extension, adding approximately 14.45 square metres to the existing dwelling. The development’s vulnerability classification is categorised as ‘More vulnerable’.
Why the Client Chose RIDA
Securing planning permission for residential extensions situated within active flood zones requires a detailed understanding of Environment Agency policies and local planning frameworks. The client required a specialist consultancy capable of providing a precise, compliance-driven assessment. RIDA was selected for its proven expertise in evaluating site-specific hazards and delivering the clear technical evidence necessary to seamlessly support household planning applications.
The Challenge
The primary constraint for the development was its location within River Flood Zone 2. The core challenge was to demonstrate that this ‘More vulnerable’ extension would remain safe over its lifetime without increasing flood risk elsewhere. Furthermore, the site’s geology consists of London Clay Formation bedrock overlaid with Alluvium superficial deposits. Strict Environment Agency policy dictated that the new extension’s Finished Floor Level (FFL) needed to be safely elevated above extreme flood levels (factoring in climate change) to ensure a robust water avoidance strategy.
The RIDA Difference
RIDA conducted a detailed flood risk assessment, meticulously evaluating the site using Environment Agency data, LIDAR topography, and the Harrow Council Strategic Flood Risk Assessment. To address the fluvial flood risks, the team analysed the proposed floor heights and confirmed that the extension’s FFL would sit 350mm above the 1% plus 35% climate change flood level—successfully exceeding the EA’s minimum 300mm safety requirement. RIDA also mapped out a safe access and egress evacuation route for future occupants via Kenton Gardens towards Kenton Road. For surface water management, RIDA verified that because the small development area is already impermeable, directing the runoff into the existing drainage system was an appropriate and pragmatic solution.
The Outcome
The detailed assessment successfully demonstrated that the proposed single-storey rear extension was completely appropriate for the site. By confirming a robust water avoidance strategy through the safely elevated floor level and outlining secure evacuation routes, RIDA ensured the project would not result in a net loss of floodplain storage, impede water flows, or increase flood risk elsewhere. The comprehensive report delivered the National Planning Policy Framework (NPPF) compliant technical justification needed to fully support the client’s planning application.