Flood Prevention Measures

Flood Prevention Measures

Having assessed the risk yourself or engaged a risk assessment consultant to do it on your behalf you have four broad strategies for flood prevention:

• Very low risk, no flood prevention required.
• Low risk of river, seawater or flash floods but a risk of basement/cellar ingress from rising groundwater.
• Requirement to prevent normal flood levels from entering a single property.
• Requirement to prevent normal flood levels from entering an area or several properties.

It should be said that a flood over a metre in depth will cause structural damage to most buildings if kept out because of the enormous weight differential between the outside and inside of the walls, so you will cause less damage overall if flooding of this depth is allowed inside your building.

How water enters a property

Above ground:

• Through doors and windows – look for gaps and cracks in joint sealant
• Through gaps around pipes, cables and other services that pass through the walls
• Through vents from boilers, washing machines and tumble dryers
• Through airbricks
• Through cracked or damaged mortar or cracks in the brickwork
• Through permeable stone, block or brick walls
• Through party walls
• At the damp proof course

Below ground:

• Blocked drains or sewers can backflow into a property
• Rising groundwater can
• - Flood a basement/cellar that is not tanked effectively
• - Enter a property through cracks in solid floors
• - Enter the space below suspended floors

Basement/Cellar Waterproofing

Tanking Systems provide a waterproof lining for a basement or cellar by coating the inside walls with a coating or membrane bonded to the structure. The treatment should be guaranteed to withstand the expected head of water, typically 5 metres or more that will cater for the height of the basement and the expected above-ground floodwater.

Sump and Pump Systems can be operated at basement and ground floor levels. They work by providing a sump (a lined hole 60cm in diameter and deep enough to provide sufficient capacity) into which rising groundwater or floodwater will flow and a pump to remove it outside of the building. The most important factor is sizing your system correctly to cope with the anticipated load. A 1 kW pump is adequate for most homes but bear in mind that the electricity supply to drive the pump may be off in a flood so consider a battery or solar driven pump.

Keeping a single property dry

Probably the most satisfactory solution for most home owners, as a dry home can be achieved relatively economically and will avoid damage to your furnishings, furniture and possessions as well the stress that this causes. However, there will still be damage to your garden, any outside structures such as garages or sheds and your car may be at risk.

Once you have surveyed the property

• Repair any weak or broken brickwork or mortar
• Consider replacing your doors or windows with flood resistant doors or flood resistant windows
• Seal gaps around services that pass through the walls
• Install a Sump and Pump Systems if required. See above.
• If you are semi-detached or terraced check with your neighbours what measures they intend to take.

Each property will require a different portfolio of measures, typically

• A supply of sandbags or custom made removable barriers to block doors, windows and patio doors. Note that although many local authorities and emergency services have a stock of sandbags; when a flood arrives they are unlikely to be available to individual homes or businesses as priority is given to hospitals, nursing homes and other vulnerable groups.
• Purchase drainage plugs and covers that can be fitted once a flood warning has been issued or fit permanent non-return valves to drains that will prevent backflow and the extremely unpleasant prospect of sewage entering your property.



• Protect airbricks and vents with covers. Some can be fitted permanently and will close in the event of a flood. Other types are clipped in place once a flood warning is issued.
• For commercial premises at risk consider installing commercial flood proof doors and windows or installing permanent flood barriers that can be operated hydraulically to seal off large door spaces.

See also: You have been flooded

Area or multiple property protection

Larger areas or multiple properties can be protected by permanent or removable barriers or portable dams. They avoid the need to do work to your property and are available as:

• Barriers that are installed into prepared fittings in embankments or riversides
• Portable coffer dams
• Plastic membranes that can be deployed around a property
• Permanently installed and hydraulically deployed barriers
• Pallet barriers
• See our Supplier Pages for links to suppliers of Removable Barriers, Permanently Installed Flood Barriers and Portable Dams.