Flood mapping is only one of several elements that should be considered when seeking to understand the flood risk to a property. Understanding the site-specific risks and vulnerabilities a property may have can be equally, if not more, important. Some of the key considerations when reviewing flood risk at the property or site scale are explained here.
Building Construction
A property’s construction is important when understanding what existing built-in flood resilience a building may have.
Some materials, particularly in traditional historic buildings tend to be inherently durable and relatively resistant to flooding compared with much modern construction (Pickles, D., 2015. Flooding And Historic Buildings. Defra.). For example, stone walls and lime mortar and plaster provide “breathability” to a property. When these materials become saturated, such as following a flood, they naturally dry out overtime with little detrimental impact on their structural integrity. Modern construction materials may be inappropriate in the renovation of historic buildings, and may actually cause damage in the long term.
Floor construction is an important factor. Both older traditional and modern buildings may have suspended floors; timber floors in traditional buildings and concrete beam and block floors in modern buildings. Voided floors provide an opportunity for flood water to enter a property through air bricks or vents, and for water levels to rise internally initially below the floors. In the case of beam and block floors, the upward pressure of the water can cause significant damage to the concrete screed. The potential for damage could be limited by implementing measures to prevent flood water entering the floor void, or by installing a sump below the floor to allow flood water to be pumped out.
Doors and low-level windows are obvious routes of entry for flood water. An assessment of door sizes, thresholds and floor levels can determine which areas are most at risk and prioritise recommendations for flood doors or barriers if necessary.
The nature of the construction of a property should always be considered when determining what flood mitigation or flood resilience measures may be appropriate or effective.
Drainage
How and where a property drains to should always be considered when assessing flood risk. When poorly maintained, drainage can be as much of a problem in exacerbating or causing flooding as it can be at assisting in removing water from vulnerable areas.
Backflow may also be an issue when flood waters reach greater depths; the head of pressure within the drainage network may force water back through the system, and ultimately cause drains and toilets to surcharge internally within a property.
Older public combined sewer systems are particularly vulnerable as they were not designed to cope with the intensity and depths of rainfall we are increasingly experiencing as a result of climate change. Sewers can quickly become overwhelmed during storm events, preventing inflows, and in some cases causing flows to back-up.
Insurance
The ability to insure a property against the loss and damage caused by flooding is also a major consideration. The implementation of the FloodRe scheme has made insurance cover for flood damage more readily available.
However, it is unlikely that the FloodRe scheme will run forever. There is an expectation within the industry that the level of cover offered by insurers in the future may become dependent on the type and extent of flood mitigation and resilience measures implemented by owners to protect their property. Understanding what measures may be required to ensure the greatest level of insurance cover can be provided may be important in the years ahead as the insurance requirements evolve.
How can FPS help?
A Due Diligence Report or Home Buyers Flood Survey can assess the flood risk to a property in greater detail, assessing flood risk and site-specific data beyond the remit of a standard property search. A Property Flood Resilience Survey can also be completed to determine how resistant or resilient the property may be to flooding, and what additional measures could be implemented to minimise the risk.
FPS Environmental Ltd are able to offer Due Diligence Reports, Home Buyers Surveys and Property Flood Resilience Surveys. If you are in the process of purchasing a property, or have recently moved in, and want to be better informed of the potential flood risk to your new home, please get in touch to see how we can help you better understand and mitigate the potential flood risk.