Boutport Street EX31 1SR
The Brief
RIDA Reports was appointed by the owner of 81 Boutport Street to provide a detailed flood risk assessment for a project in Barnstaple. The proposed development involves the demolition of the rear extensions of an existing listed building.
Why the Client Chose RIDA
Given the property’s listed status and location within a flood zone, the client required specialised expertise to evaluate flood risks accurately and outline resilient design strategies. RIDA was chosen to deliver a robust assessment that would ensure compliance with the National Planning Policy Framework (NPPF) and support the required listed building and planning applications.
The Challenge
The site is located within Flood Zone 2, indicating a medium probability of fluvial flooding, with the River Taw situated approximately 200 metres away. A key constraint was that the exact design water depth was unknown, leading to a conservative assumption of potential flood depths between 300mm and 600mm above the ground level of the building. Additionally, the final floor level of the new alterations had to match the existing building’s ground levels, meaning that removing the development from the flood hazard through raised thresholds was not feasible.
The RIDA Difference
RIDA conducted a detailed flood risk assessment using Environment Agency maps and the standing advice approach to evaluate fluvial risks. To address the specific constraints of the site and the inability to raise floor levels, our team specified a dual approach: a ‘water exclusion strategy’ for flood water depths up to 300mm, and a ‘water entry strategy’ for depths between 300mm and 600mm to avoid structural damage. We recommended the use of highly flood-resilient construction materials classified as “Good” against water penetration, such as minimum 150mm thick suspended concrete floor slabs. Furthermore, we outlined a safe egress route for occupants via Boutport Street towards Queens Street, and recommended the use of Sustainable Drainage Systems (SuDS) to manage surface water run-off.
The Outcome
The comprehensive assessment successfully demonstrated that the proposed works would be safe for the building’s 50 to 100-year design life without increasing flood risk elsewhere. By incorporating a resilient design for water entry, the report confirmed full compliance with the NPPF and provided the necessary drainage principles to safely progress the planning and listed building applications.