Designing Flood-resilient Homes
8 Nov 2018
Abode at Great Kneighton in Cambridge, designed by Proctor & Matthews Architects
Water damage is the number one cause of property insurance claims in the UK – which is perhaps why 87% of respondents to the survey viewed flood resilience as an important factor in the choice of a new home. The latest guidance for designers, BS 85500:2015, recommends the use of a range of concrete and masonry structures, as they retain their structural integrity after a flood. Concrete has the strength to keep water at bay and has few construction joints to let the water through.
It can be designed to resist very high loads, and is robust enough to withstand impact from debris. But it doesn’t only help to keep water out of a property. It is also easier, compared with materials such as timber, to wash and disinfect if water does get in, and it is more resistant to rot or fungal growth.
This helps to reduce costs and disruption, particularly for shortduration floods. Reinforced concrete or concrete blocks can be used as the structural wall in a solid-wall solution, or as one or both of the leaves in a cavity-wall construction.
Another approach is to adopt an insulated concrete formwork (ICF) system, which uses rigid insulation as the mould within which ready-mixed concrete is cast, before being finished with a surface treatment. The insulation properties are unaffected by moisture, making ICF appropriate for most flood situations.
Where it is not possible to place the ground floor above the predicted flood level, a reinforced concrete slab, at least 150mm thick, is the preferred construction solution. This should ideally be groundbearing to avoid water and mud getting under the building.
Deeper floors are likely to require thicker slabs to maintain their structural integrity – for example, a 200mm slab for a 450mm flood above ground level, or 300mm for a 600mm deep flood. Rigid closed-cell insulation is the preferred choice for all parts of the building likely to be affected by flooding, as it is able to retain integrity and resist moisture absorption.
In floors, a minimum 1,200-gauge damp-proof membrane is also recommended. Suitable floor finishes include ceramic or concrete-based floor tiles that are robust, water-resistant and easily cleaned after a flood..