Chris Hodson from Interpave explains the importance of taking a responsible approach to rainwater runoff from paving around both new and existing homes to protect them and the wider community
Another year of flooding around the UK provides a timely reminder of the importance of sustainable drainage (SuDS) and permeable paving in the fight against flooding. As our towns and cities continue to grow, more rainwater is captured on streets, car parks, drives, roofs and other sealed surfaces – which then flows into sewers, rivers and streams. Existing drainage systems simply cannot cope, causing downstream flooding.
In addition, roads, car parks and driveways collect pollution – from car exhausts, tyre and brake wear (including electric vehicles), oil leaks and other sources – and when it rains this gets washed into sewers, harming rivers
and streams.
WE MUST ACT NOW
Climate change means more frequent and heavy rainstorms leading to more flooding. This is because ‘sealing up’ our towns and cities also stops rainfall soaking into the ground naturally. The water table levels drop causing more water shortages, streams and ponds to dry up, and trees to be deprived of water. It could also affect the foundations of your home, particularly on clay soils, as they dry out and shrink.
These problems are made worse when gardens are sealed-up too, particularly when water runs straight to roads and sewers. Of course, one small area of paving in isolation is not going to cause major flooding – but the cumulative impact of numerous properties can. For example, the area of paving in front gardens for car parking in London is equivalent to around 5,200 football pitches. Simply allowing rainwater to run straight off roofs and paving into drains is no longer an option.
SUSTAINABLE DRAINAGE SOLUTIONS
For over 20 years, it has been recognised that SuDS are essential in curbing flooding and pollution from rainwater runoff. SuDS manage 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.
SuDS manage rainwater near the surface and as close to its source as possible, 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.
For new developments, SuDS will generally be required as part of the planning process, although this will depend on which part of the country. In some cases, a single house may be exempt but, increasingly, local policies affecting planning applications will demand SuDS. For example, the ‘London Plan’ says that “development proposals for impermeable paving should be refused where appropriate, including on small surfaces such as front gardens and driveways”.
Using SuDS is a low-cost solution, and the responsible thing to do.
PAVING AROUND EXISTING HOMES
For some time now there has been wide-ranging encouragement to use SuDS widely. Although changes to planning rules in both England and Scotland were instigated years ago, growing awareness of the importance
of permeable paving in the fight against flooding means increasing enforcement by local authorities in the light of climate change.
Installing drives or other paving anywhere in your garden used to be considered ‘permitted development’ – in other words an automatic planning permission. But these rights have been removed from new or replacement paving – unless it’s ‘permeable paving’ or drains onto a permeable area within the property, planning permission will need to be sought.
If you are creating a new drive or parking space, you must also have ‘dropped kerbs’ onto the public highway with a special highway authority licence and, in some cases, planning permission. Again, the drive should meet ‘permeable’ requirements and not drain water onto the road. Going against these requirements could result in local authority enforcement action or legal problems when the house is sold.
PERMITTED PAVING
Interpave’s ‘Paving for Rain’ – referred to in government rules and free to download – offers guidance on concrete block permeable paving, which allows rainwater to filter through grit-filled joints between the blocks to store the water for a short time, and rain gardens – where conventional paving simply drains to a landscaped depression, maybe with plants, to hold water.
In both systems, water is held back on your property during heavy storms to avoid flooding and filtered to remove or trap pollution. What happens next depends on the ability of the ground to absorb water (known as ‘permeability’) and whether you want to recycle the rainwater.
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. They 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 gullies 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 to planting – particularly trees. In fact, it works in harmony with trees allowing air, as well as water, to reach tree roots, so that they grow downwards and don’t damage the paving over time.
Chris Hodson is a consultant to the trade body Interpave