Chris Hodson of Interpave delves into the impact of soon to be mandatory sustainable urban drainage systems (SuDS) in new residential projects, and the transformative role that permeable paving plays

The wider application of concrete block permeable paving to reverse the flooding from the sealing-up of our towns and cities is heralded by new measures to implement SuDS in England.

For some 25 years it has been recognised that Sustainable Drainage Systems (or ‘SuDS’) are essential in curbing flooding and pollution from rainwater runoff. SuDS manages rainwater by slowing it down and cleaning it up – copying, as closely as possible, the natural drainage from a site before any building work takes place. They operate near the surface and close to the source of runoff, slowing the flow and providing additional benefits including clean water for wildlife, planting or recycling. Typical SuDS include living (or ‘green’) roofs and permeable paving, as well as planted features like rain gardens.

MANDATORY SUDS

The 2010 Flood and Water Management Act included provisions for mandatory SuDS on developments, controlled by new local authority ‘SuDS Approving Bodies’ (SABs). But these provisions were not implemented at the time in England – although they were in Wales – relying instead on planning policies to deliver SuDS. Recognising that the planning-based system has not worked, the Government is now implementing Schedule 3 in England to make SuDS mandatory – currently expected during 2024.

New SuDS standards and other changes will then be applied, and SAB approval will be required before construction of drainage systems on new and redeveloped sites. Single homes may well be exempt from SAB approval but SuDS could still be encouraged by other means, such as planning policies. This is an important step forward, not just in the fight against flooding but also in enabling the numerous multifunctional benefits of well-designed SuDS to be realised, particularly in response to climate change. 

ACTION ON EXISTING PROPERTIES

The welcome move towards wider use of permeable paving will help to reverse the ‘sealing-up’ of our towns and cities, highlighted in the government’s recent National Infrastructure Commission (NIC) report on reducing flooding from surface water. This recommends urgent action to move away from impermeable surfaces, both for new developments and on existing properties. 

The NIC recognises that, by 2055, some 50,000-65,000 properties may be put in areas at high risk due to “unplanned” increases in impermeable surfaces, such as front gardens being paved over, which increase the volumes of water entering drainage. 

PERMITTED PAVING

Installing drives or other paving anywhere in your garden used to be considered ‘permitted development’ – in other words, automatic planning permission. But these rights were removed some years ago from new or replacement paving unless it’s permeable paving or drains onto a permeable area within the property. Otherwise, you will need to apply for planning permission, involving drawings and a fee, and with policies in favour of SuDS, the application should be rejected anyway. If you just go ahead without permission, this could result in local authority enforcement action or legal problems when the house is sold. 

However, enforcement of these rules has been limited and now the NIC is seeking a review of options for resolving this issue and potential policy changes to prevent it from adding to the flooding problem. In addition, some water companies already apply ‘area-based charging’ to commercial properties where impermeable paving drains to sewers and Ofwat is encouraging trials with residential customers as well. We shall soon see a much wider application of permeable surfaces – notably concrete block permeable paving – reversing the sealing-up of urban areas we have seen. 

MAKING THE MOST OF PERMEABLE PAVING

There is a wide choice of products available from manufacturers specifically for permeable paving, with more shapes, styles, finishes and colours than ever. Some products have the
same performance as conventional concrete blocks and slabs: slip resistant, durable, strong and sustainable. The difference with permeable paving is joints filled with stone grit – but never sand (like conventional block paving) or mortar. This ensures that water will continue to pass through the joints over many years. 

Concrete block permeable paving can be laid level and still avoids puddles without the need for drainage gulleys and pipes. It provides a safe surface for everyone, unlike gravel and other loose material. It can also provide a gradual supply of clean water for planting – particularly trees. In fact, it works in harmony with trees, allowing air, as well as water to reach tree roots, which grow downwards and don’t damage the paving over time. 

Chris Hodson is a consultant to trade body Interpave, part of MPA Precast