There are many barriers to building the new homes we so urgently need, but puddles are perhaps the most surprising
Paul Smith is Managing Director of The Strategic Land Group
There are many barriers to building the new homes we so urgently need, but puddles are perhaps the most surprising – and one of the easiest to fix. Surface water flooding is the planning jargon for what happens when it rains so hard that drainage systems become overwhelmed – puddles, in other words, albeit often big ones.
Current planning policy requires surface water flooding to be dealt with in exactly the same way as flooding from rivers.
To secure planning permission for new homes, developers must first show that there are no alternative sites which are at a lower risk of flooding – called the sequential test. This involves looking across the whole of a local authority area, and considering both individual sites and combinations of sites which could deliver the same development. Local authorities can do that work as part of plan-making, but if a site isn’t allocated for development in the local plan, developers must do it themselves. That takes time and costs a lot of money – typically £20,000 or more.
If the sequential test is passed, developers must next contend with the exception test – showing how future occupiers of the site can be made safe from flooding, without making flooding more likely elsewhere.
This is all entirely reasonable as far as flooding from rivers is concerned – there aren’t many other ways it can practically be dealt with – but surface water flooding is of an entirely different character. It is caused, remember, by drainage systems failing to cope with the sheer volume of rainfall. There is an easy solution to that – upgrade the drainage system.
That’s exactly what developers are required to do when delivering new homes. They calculate the likely amount of rainfall that will fall on the site, add in a contingency for the wetter weather and more intense rainfall we’ll see as a result of climate change (the Environment Agency has 3,200 words of guidance on what that allowance should be), and then design a drainage system to deal with it all.
These sustainable drainage systems involve combinations of features like swales and rainwater gardens, which allow water to soak into the ground, alongside ponds, basins and underground tanks which store rainwater at times when rainfall is highest, before gradually releasing it. The result is a drainage scheme that deals with all the likely rainfall both now and in the future, without increasing the risk of flooding elsewhere.
That may sound like a common-sense approach – and it’s exactly the way surface water flood risk was dealt with until early 2024 when a court judgement revealed everyone had been misunderstanding policy all along. Rather than recognising that the new drainage scheme would address any potential flooding issues, the result was that surface water flooding was to be treated in exactly the same way as flooding from rivers.
Surface water flood risk is far more widespread than flooding from rivers – look at the Environment Agency’s recently updated flood map and you’ll see the country is pock-marked with potential puddles.
If the Environment Agency’s map shows some surface water flood risk on a site, developers have three options, all equally unpalatable.
The first is to attempt to pass the sequential test, an exercise likely doomed to fail due to the large areas that need to be searched for potential alternative sites.
The second is to carry out site-specific modelling to show the Environment Agency mapping is wrong. It often is – the data used to prepare the maps is better than it used to be but still quite crude. Proving that, though, costs tens of thousands of pounds and takes many months, in part because input is needed from the Environment Agency at various points in the modelling process.
The third is to simply design around the surface water flood risk shown on the Environment Agency’s map, avoiding putting homes, roads or even changing the ground level of those areas so that the requirement for the sequential test isn’t triggered. For some sites that will be easy, for others the location of the potential flood zones will create awkward-looking layouts that fail to use the land as efficiently as possible.
This is having a very real impact on the delivery of new homes. Planning applications and appeals are already being refused for failing to deal with the policy correctly. A survey of just 20 members of industry body the Land, Planning and Development Federation found that applications for 57,000 new homes were being delayed between them. Extrapolate that figure across the development industry as whole and the number of delayed applications will comfortably be in six figures – on a par with the nutrient neutrality issues that the government has invested so much time in resolving.
If this delivered a reduction in flood risk, perhaps it would be warranted – but it doesn’t. The current approach delivers worse outcomes than what it replaced. Instead of drainage schemes simply reflecting the risk of surface water flooding and dealing with it, the low points on sites where surface water is likely to accumulate as puddles are being left untouched, prone to flooding for ever.
Most frustrating of all is how easy this is to fix. The Planning Practice Guidance could be updated tomorrow to make clear the sequential test is not required for sites which are only subject to surface water flood risk, and where the surface water drainage scheme takes that into account. All those stalled sites would be unlocked without reducing development quality, and the number of new homes being built would increase. The result would be new homes for children who like splashing in puddles, rather than puddles preventing their construction.
This piece is sponsored by the Land, Planning and Development Federation (LPDF).
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