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Assessing Flood Risk

The easiest way to assess if your house is at risk from flooding is to find out the history of flooding in the surrounding area. For example, your house may be at risk from flooding if it has flooded in the past or if flooding has previously occurred in the locality. If you have not lived in the area long, your neighbours or a local historian might know if any floods have previously occurred.


You can check a number of OPW websites that provide information about flood risk:

  • Information on past flood events and predictive flood maps are available at
  • Coastal flood hazard maps are available on the website.

Another way to assess the risk of flooding in your area is to study the surrounding land and water courses. You could be at risk from flooding if:


  • Your house is near an open water source, such as a river, the sea, a lake, a stream, ditches or drains.
  • Your house is in a hollow or a low-lying area where floodwater could collect.
  • Your house contains a basement.
  • The Ordnance Survey maps indicate ‘liable to floods’ at the location of your property.

If your property fits into any of the criteria then you could be at risk from flooding due to:


  • Rainfall filling rivers, streams, ditches and urban drainage systems beyond their flow capacity.
  • Floodwater overflowing river banks and flood defences onto floodplains.
  • Coastal storms leading to the breaching of coastal flood defences due to storm surge and wave action.
  • Blocked or overloaded drainage ditches, drains and sewers overflowing across roads, gardens and into property.
  • Overloaded sewers back flowing into property.
  • Rain that is so heavy that run-off flows overland down hills and slopes.
  • Rain soaking into the ground causing ground water levels to rise and flood.

It is important to remember that while flood defences, such as walls or embankments, do provide some protection against flooding, they do not provide total protection. Flooding of areas behind such defences can occur from water behind the defences being unable to drain away (such as storm water from heavy rain) or from floodwaters spilling over the top of defences in particularly extreme events. If your property is behind a defence, it will flood less frequently than if the defences were not there, but it will still be at risk.

Above Ground

Floodwater can enter your house above ground in the following ways:


  • Through doorways and windows (even if they are closed!).
  • Through airbricks or other ventilation openings.
  • Through other gaps and around pipes and cables that pass through walls.
  • Through party walls if the property next door is flooded.
  • Through cracks in the brickwork.
  • Through permeable, weathered or damaged brickwork, blocks, stone and mortar.
  • At the damp proof course.

Below Ground

Below-ground floodwater can enter your house in the following ways:


  • Rising up through the floors (or through the walls of cellars or basements) in areas where the ground is made of permeable material, such as chalk, gravel or sand.
  • Through drainage trenches in impermeable ground.
  • Through drains and pipes leading into the house including:

– Toilets
– Sinks
– Baths
– Washing Machines
– Dishwashers