We’re often asked to justify why our Floodgates are “only” 68cm high and can’t we make taller barriers to cope with deeper floodwater. We also get asked whether it would be better to fit a flood-proof door, so we will attempt to address both these issues here.

Why only 68cm high?

Our Floodgates are designed to protect from flooding up to 60cm deep with an additional 8cm to allow for small waves, typically caused by wind and passing vehicles. The reason for selecting 60cm as the “magic number” was from research into the strength of conventional brick built cavity walls.

Planning Policy Statement 25 Practise Guide written by the department for communities and local government, highlights the need to allow flood water above 60cm to travel through a property as, the weight of the water (hydrostatic pressure) on the outside of the wall risks permanently damaging the wall. If the flood level exceeds this limit it is necessary to allow the water to reach the inside of the wall to equalise the pressure. This should be done gradually to avoid what is known as catastrophic failure – completely removing the existing flood protection at this point would likely cause significant damage as the water rushes into the property, through the doorways. Allowing the Floodgate to “overtop” means that there will be a gradual influx of water until the levels equalise on both sides of the barrier.

What do you do when your flood door breaks?

In the aftermath of Storm Desmond in 2015, over 60 people in Cumbria had flood doors installed which have subsequently failed to perform as intended – It is important to note that not all doors failed but, for the owners of those that did, that is not much consolation. See this item from BBC News for more information:  https://www.bbc.co.uk/news/uk-england-cumbria-47203766

Flood Door or Flood Barrier?

We think that flood doors are a bad idea. This is not because we make flood barriers – quite the opposite – we make flood barriers because we think that flood doors are a bad idea – otherwise we would offer both options. Here is our reasoning…

  1. Our first concern is safety. If you think about a situation where you are flooded and you have a flood door – how do you get out of the property or how do others, such as the emergency services get in? Once the door is closed and there is flood water on the outside, you have effectively lost the use of the door until the flood water has receded. If you have a flood barrier like our Floodgate, as it is erected on the outside of the door you can continue to open the door and step over the barrier if you need to. A simple fact but, one that can make the world of difference. If you read the story of the Fowey Bakery (link) Even while they were flooded, their customers still waded through the water to buy their bread being served over the Floodgates.
  2. A flood barrier is engineered to be used in the extreme situation of flooding but, you mainly need a door to cope with everyday use, opening, closing, being locked and unlocked many times a day. Trying to engineer a door capable of performing both functions is possible but the end result will be very expensive and extremely heavy for everyday use. Current designs, as evidenced in the BBC report referred to above, are a compromise but the result is an unacceptable failure rate on both counts as a door and as a flood protection device.