Flood resilience

Flood resilient construction uses methods and materials that reduce the impact from a flood, ensuring that structural integrity is maintained, and the drying out and cleaning required, following inundation and before reoccupation, is minimised.

Concrete is inherently water resilient and entirely suitable in a construction designed to be either waterproof, as required for water barriers, or water resilient. The extent to which the structure keeps out water depends on the specification of the concrete itself and its design details, corner junctions for example.

Categorisation of the flood resilient properties of various construction materials and guidance on appropriate flood management strategies is provided in the Department of Communities and Local Government publication Improving the flood performance of new building: Flood resilient construction.  

A water exclusion strategy, or resistance, for low depth flooding, is designed to prevent floodwater entering the building and minimise the impact of floodwaters and to give occupants more time to relocate ground floor contents.

A water entry strategy, or resilience, for greater flood depths includes measures incorporated into the building to reduce the impact of floodwater on the property once water has entered.

Insitu and precast concrete has low permeability so resulting in minimal damage or deformation from a flood. It is appropriate for use in buildings that require either a water exclusion strategy or a water entry system, where other construction techniques could incur structural damage due to excessive differential pressures.

Summary of water exclusion strategy construction details:

• Concrete foundations: provide a barrier to water entry into the wall cavity.
• Floors: Ground supported concrete slabs of min. 100mm thick can prevent loss of structural integrity due to uplift pressures due to water ingress from the ground.
• Walls: Clear cavity or solid masonry walls offer better flood resilience than filled or part-filled cavity walls.

Summary of water entry strategy construction details:

• Floors: As for the water exclusion strategy
• Walls: As for the water exclusion strategy. Note: to meet current standards high density internal insulation can be used. Concrete blocks dry more quickly than Aircrete blocks. Internal cement renders should be avoided as these can prevent effective drying.

Concrete proof

The floating house concept was developed by Factor Architecten in Holland. The two-storey houses are each built upon a 70t watertight concrete box which not only provides buoyancy in times of flooding but also provides additional living space in the form of a basement.

When flooding occurs, the homes can raise up to 15ft by floating on the water, guided and kept in place by two concrete piles. The floating house concept proves concrete's credentials of watertightness and robustness, valuable assets for flood-prone areas.