Anti-flood measures are an essential part of our response to climate change, not just a topic for winter or for high-risk locations
Adaptation is an essential component of responding to climate change, and flood resilience is a core consideration. Currently around one in six UK properties are currently at risk of flooding, and this is set to double by 2050 due to changing weather patterns and increased urbanisation.
Designing out avoidable repair and maintenance and extending the usable life of buildings or components will be key to achieving a net zero carbon society – repeated replacement of water damaged fittings and fixtures has little place in a circular economy.
The threat of water damage is not limited to identified flood risk areas near our rivers and coasts. Surface-water flooding, burst water mains and blocked drains affect all buildings irrespective of location. Choosing a water-resilient structure reduces not only the potential damage from external sources, but also other events such as undetected leaky pipes.
In recent years a greater focus has been put on measures that can be introduced to existing buildings, either during repairs after a flood, or in anticipation of one. But as with retrofit measures for improving energy performance, it is widely recognised that improving flood resilience is much easier when considered from the outset – that is, in new buildings rather than as retrofit measures.
Designing for resilience
Establishing the type of flood event likely to affect a property is fundamental to establishing an appropriate solution. The design strategy should be based on anticipated flood depth, likely duration and source of flooding, but also take project specific factors into account such as the cost of construction, the cost and impact of repair, and ability to recover after a flood.
The first step is avoidance: locating the property at area of least risk and/or raising it above the predicted flood level. The second is site layout: using the landscape to reduce flood risk or delay its impact on the building, without increasing risk elsewhere, using features such as bunds, sustainable urban drainage systems and storage. Mitigation is the final step, where the layout, choice of construction materials and detailing are developed to keep the water out as far as possible, and minimise damage and speed up recovery when it does get in.
The strategies for improving the flood resilience of an existing property are far more complex than for a new-build. It is rarely practical to raise floor levels above the predicted flood level, and opportunities for external measures to delay water ingress can also be limited. Mitigation of the building fabric, fixtures and fittings are therefore the main area of focus – but the limitations of existing layouts and sheer range of construction types mean any solutions must be tailored to specific situations.
It is important that the structure of a building is not compromised by a flood, as this is the most costly and disruptive part to replace. A quick recovery with limited additional expenditure and resources is clearly desirable, and here concrete and masonry construction offer significant advantages.
Its performance is not affected by being submerged, or from drying out. Unlike framed solutions, it can also be installed without voids and with very few joints, helping to keep water out. All the recommended and preferred wall and floor constructions in the current British standard are made from concrete or masonry.
Concrete and masonry can be both structure and final finish, offering the ultimate in material efficiency both during construction and after a flood. The time taken to dry out some types of water-saturated masonry is sometimes seen as a disadvantage to speedy reoccupation, but this is not an issue with an internally lined and drained solution.
Very slow to absorb moisture, concrete can even be water-resistant, as in basement and swimming pools. There are also numerous clear surface-applied sealants that can limit moisture ingress.
Concrete and masonry walls, floors and stairs, can provide resilience at the core of any building, even if all other measures are not installed from the outset. They can facilitate the application of further resilience measures in the future, as risk of flooding increases, especially if a whole building strategy has been considered from the outset.
By embedding good flood-resilience thinking and materials in this quite simple way, we are better preparing our building stock for the future. “Be prepared” has become a mantra for those living with the risk of flooding, and surely all architects and developers should heed this advice.
Elaine Toogood, Head of Architecture at The Concrete Centre.