How to flood-proof your property and when to seek help

By Michael Jones, National Waterproofing Manager at Peter Cox & Rentokil Property Care, and Jamie Woodhall, Innovation & Technical Manager at Rentokil Specialist Hygiene 

According to the Met Office, this summer was one of the wettest in the past 10 years. And, as the world warms, the UK is forecast to receive even more rainfall in the future, making extreme weather and flash floods much more likely to occur. With one in six (around 5.2 million) properties in England already at risk of flooding from rivers or the sea, increased levels of rainfall could put even more buildings at risk.

Floodwater often contains sewage or household waste, so it can be a health hazard, while there’s also the potential for it to cause structural and financial damage to a property. At a time when the government is encouraging people to build their own homes, it’s important that anyone undertaking a self-build or renovation project is aware of the waterproofing processes involved, to help ensure their home is adequately defended.

Resistance vs resilience

For properties being built in at-risk zones, it is important to assess protection measures before floods occur. These actions fall into two categories: flood resistance and flood resilience measures.

Resistance measures prevent water from entering areas by creating watertight barriers. These minimise the likelihood of floodwater entering a building and causing damage. This can include temporary flood resistance products which require fitting prior to an expected flood event, or permanent flood resistance products that provide constant protection. Barrier Waterproof membranes and drainage systems are very effective resistance tools for protecting properties.

Resilience measures are designed to mitigate and reduce the damage caused by flooding in a property, covering situations where water enters the structure.  These measures are often included in the building’s fabric or fixtures, for example moisture resistant tiled floors,  masonry protection cream, which repels water penetration through masonry and can also improve thermal efficiency. 

General design philosophy

One of the most effective steps to prevent water ingress in a building is to adopt a combined approach, This approach of combining below ground waterproofing and flood resilient design strategies for both types of event in one building is given credence in BS 8102 2009 “Code of practice for protection of below ground structures against water from the ground” and BS 85500 2015 “Flood Resistant and Resilient Construction”.  

Repair mortars and waterproof slurry coatings to stop or slow down water ingress will initially need to be applied to the internal faces of the structure of the property. On the basis that water will enter eventually you would also need to install an internal protection system to both preserve finishes and drain any water away. This can be done by installing Type C cavity drainage membranes over the floors and walls.

Such membranes act to control and divert water via drainage channels and floor gullies to sump and pump units, which will pump the water out through external walls above the external flood level. The membranes can stay in place and will allow the structure to passively dry following a flood event whilst allowing re-occupation within their envelope, speeding up re-occupation time. 

When having conversations with contractors, be sure to ask if they’re aware of what these are – and how they are going to help ensure your premises is properly flood-proofed.

In case of ‘overtopping’ during protracted periods of ingress or bypassing of prevention measures such as accidentally leaving a door open, the internal finishes should be designed to be resistant and “recoverable.” This is most commonly achieved by using finishing materials that don’t swell or expand when exposed to water, or have water resistant properties to prevent damage to the property’s structural elements.

In the event of a flood

In the case of flooding, prevention is always better than a cure – as damage is not only costly but it can also be extremely traumatic.

It’s important to remember that exposure to flood water can cause infections to wounds, rashes, gastrointestinal illness, tetanus and in some cases leptospirosis. If you need to enter floodwater for any reason, it is advisable to wear protective clothing including gloves, overalls and facemasks. After exiting floodwater, be sure to wash yourself and any reusable protective items thoroughly and dispose of any other protective gear appropriately. For this reason, it’s often better to call in the experts when extreme flooding is experienced.

In these cases, professionals will help to reduce flood levels outside the property and then use a generator powered pump to remove the majority of the water inside. Following this, all furniture, fittings and appliances will be removed as necessary to reduce the chances of mould forming. Experts will also take caution when removing large silt or mud deposits as there may be structural damage caused to the property that is not immediately obvious.

Final thoughts

Given the complexity of waterproofing a building, a design specialist should always be involved as early as possible. While compliance with waterproofing, flood resistance and resilience standards can be an added cost, cutting corners can lead to the building’s structural integrity being compromised, which could cost far more to repair damage and replace fixtures and fittings if something does go wrong in the future. If you are unsure of the correct approach to property waterproofing, then it’s always best to get in touch with the experts.