Me and My Flood

9 Nov 2018

Next week is London Flood awareness week and it got me thinking about my own situation and response to a potential flood.  I live in central London and so, for now at least, feel well protected by the Thames barrier from any large-scale tidal flooding event. But I have been flooded in the past, the result of a blocked drain in my back yard. Luckily my ground floor extension is made of rendered concrete block and raised up a step and so the full depth of the flood water did not enter my property. The floor is concrete with large tiles, so the water that did get in was easily mopped and cleaned away, leaving no permanent damage to structure or finishes.  

More by luck than judgement, these design decisions aligned with the latest guidance for designing for flood situations: Standard BS 85500:2015 Flood resistant and resilient construction - Guide to improving the flood performance of building.

This guidance adopts a hierarchical design approach to design for minimising the impacts of flooding, which can be summarised as Avoidance, Resistance and Resilience. The first principle is to build beyond or above identified flood-risk areas. Any habitable ground-floor level should be above the anticipated flood level where practically achievable. External flood-protection measures, including local bunds or concrete and masonry walls, can be designed to protect individual or groups of houses from flooding, but this can potentially exacerbate neighbouring flood risk areas. The risk from surface-water runoff can be reduced using SuDS, including permeable paving, pervious concrete, storm-water storage and green roofs.

A ‘water exclusion’ or resistance strategy, uses measures to prevent or reduce the entry of water into a property. It is most effective for water depths of 0.6 metres or less and relies on appropriate wall and floor construction as well as the blocking all openings, such as doorways, pipes and vents.

A Resilience, or ‘water entry system’ has construction designed to reduce the impact of flood water when entering the building, limiting the extent of damage caused, maintaining structural integrity and making drying and cleaning both quicker and easier. The term ‘recoverability’ is used to describe this strategy and ‘resilience’ is used to describe the combination of measures to reduce the impacts of flooding. In BS 85500 the recommended new wall and floors are all forms of concrete and masonry construction.

Of course, as a small extension, in my location, there was no requirement to submit a detailed flood risk assessment and so such considerations where not part of my design development at the time. They would be now.  I know now that you don’t have to be close to a river or coast to be at risk. Surface water flooding, burst water mains and blocked drains are flood hazards affecting all housing irrespective of location.

Being part of the team developing the Property Flood Resilience (PFR) action plan, an initiative to raise awareness and improve recovery from flooding nationwide, I am now much more aware of the widespread and increasing likelihood of floods and their impact.

PFR action plan initiatives to date include new training courses and certification schemes for flood professionals, a web based hub for guidance and links to resources (www.floodguidance.co.uk )  and the live projects demonstrating practical methods for improving the flood resilience of existing properties, including the Cumbria Flood Resilient Showcase Project  and the Flood Resilient Repair House at BRE Watford. A new code of practice and guidance for property flood resilience is also underway as well as other campaigns to help drive behaviour change.

I urge everyone to check their current and predicted flood risk when embarking on refurbishment, extension or new build. Some simple measures, taken early in new design development, can make a big impact in reducing risk and aiding recovery.   

Elaine Toogood, senior architect at The Concrete Centre