Finished Floor Level
FFLThe final level of the ground floor of a building, set above the design flood level plus freeboard to protect against flooding for the development's lifetime.
The finished floor level (FFL) is the final constructed level of the lowest occupied floor of a building, specified in metres Above Ordnance Datum (m AOD). In flood risk terms, the FFL is the critical design parameter that determines whether a building will remain dry during a design flood event.
The FFL is derived by taking the design flood level — which incorporates the appropriate climate change allowances for the development’s lifetime — and adding freeboard. This combined level ensures that habitable floors remain above floodwater even under worst-case modelled conditions.
Setting the correct FFL is a central outcome of every Flood Risk Assessment. The specified FFL influences:
- Architectural design: The building must be designed so the ground floor is at or above the FFL, which may require changes to entrance thresholds, ramps, or internal layouts
- External levels: Surrounding ground levels, car parks, and access roads must be graded to maintain safe access at the FFL
- Flood resilience: Where it is impractical to raise the entire ground floor to the FFL, flood-resilient construction techniques may be accepted as an alternative for non-habitable spaces (such as garages)
In areas with significant flood depth, achieving the required FFL can be a major design constraint. Strategies include raising site levels with imported fill, constructing buildings on stilts or raised podiums, and locating ground floors above undercroft parking.
The FFL is typically conditioned on the planning permission and must be achieved before occupation. Aegaea’s flood risk assessments specify the required FFL clearly, supported by survey data and hydraulic modelling outputs.