Is your paved driveway putting your house at risk?

When Mary Long-Dhonau moved into her new home, at the top of her list of DIY improvements was to pull up all the ugly paving in her garden and replace it with gravel. She also put back in the lawn and added a water butt to collect water coming off her roof, to stop her drains being overwhelmed. 

Her preoccupation with flood defences was not because her new home was near a river or a stream, but because past experience had taught her just how destructive surface floods can be.

She remembered the devastating floods in 2007 that damaged 55,000 properties and left 1.2 million without water and power. Two thirds of this devastation came from surface water flooding, not rivers bursting their banks. Today, the Environment Agency says that three million homes are at risk of surface flash flooding. And this week, a report from the National Infrastructure Commission stated that more than 600,000 English properties could be in areas at high risk of surface flooding by 2055. 

The NIC singled out one feature in particular for its danger: impermeable surfaces – mostly, paved driveways – that stop rainwater running off into the ground. This is the reason, the NIC says, that 65,000 more properties are being put at risk of flooding in future. Could your driveway cause your house to be wrecked?

In 2005, the Greater London Authority published a report saying an area 22 times the size of Hyde Park had been paved over in London’s front gardens. Ten years later, a study by the Royal Horticultural Society stated that paved front gardens had risen threefold in a decade from 2005.

In July 2021, when parts of London received more than twice the average monthly rainfall in just two hours, the impact was just what you might expect when water is unable to soak into the ground. Of the 1,500 properties that were flooded, half had paved-over front gardens. 

It’s a similar story all over the UK, but particularly in areas of urban creep and infill. 

Whether it is because people need more space to park, or because of a growing disinclination to mow the lawn and tend the shrubs, front gardens across the UK have been falling to tarmac; the only region to have reduced the number of paved gardens is the North East, which has boosted planted front gardens by 50 per cent.

Factor in climate change, which causes unpredictable deluges anywhere and at any time of the year that can overwhelm our drainage systems, and the result is flash flooding. 

If you weren’t already tempted to take a pickaxe to that driveway, then you might be if one of the NIC’s proposals is implemented: that water companies should levy charges based on the area of a property that is paved with a non-permeable surface.

For a certain kind of householder, those for whom their home is their castle and their driveway is its drawbridge, such an idea will seem outrageous. 

But, as Long-Dhonau says: “If we all took small moves to reduce our flood risk at our own property level, then collectively we could make a significant reduction to our own flood risk. At the same time, we would be ‘greening up’ and supporting nature and wildlife, which in turn could have health benefits for us all. We would all enjoy nature thriving around us, the air we breathe would be cleaner, and our mood uplifted, so what’s not to like?”

However, laying the responsibility for preventing flash floods at the doorsteps of homeowners up and down the  country is an oversimplification of the problem.

While Alastair Chisholm, from the Chartered Institution of Water and Environmental Management, fully supports the recommendations of the NIC, he says: “It’s not all about driveways, but all kinds of hard surfaces gradually getting added in to urban areas and taking away the more natural ground that water can filter into.”

Part of the problem is the extra outbuildings that have been built around homes, particularly since the pandemic when it became fashionable to have an outside office. 

Another factor is our failure to implement sustainable drainage solutions as building standards. When Chisholm built an extension recently to his own property, he took care to install a water butt and disconnect his downpipe from the gutter so that instead it runs into a planter or soakaway in his garden.

Any excess rainfall will then be filtered into the ground, rather than into the sewer system. Part of the reason that there have been so many scandals with sewage pollution is because of heavy rainfall causing the systems to become overburdened.

While Long-Dhonau calls paved driveways a “bugbear” of hers, the reason she has become an expert on the subject of surface flooding, earning an OBE for her work, is because her previous home in Worcestershire was flooded a total of 12 times before the water board got to grips with the problem. Her home, it transpired, was located at a pinch point in the drainage system. If there was big rainfall, the manholes would pop. 

The fact that so much of the ground was paved then amplified the problem, but was not the cause. In the end, and after a lot of campaigning, the water company paid for a pumping station to deal with the problem. 

Recent sewage flooding has led to campaigners demanding we upgrade our sewers, which were built more than 100 years ago to cope with fewer and less intense storms than the frequent heavy rain we now experience. Drains are also not maintained as frequently as they once were, owing to squeezed local authority budgets. “They’re being done once a year where it used to be two or three times,” says Chisholm. 

Replacing all these sewers just isn’t practical: “Honestly, there are hundreds of thousands of miles of them and it’s not just the Victorian ones – this was the way we built sewers until the 1960s at least.” Instead, we should be aiming to keep more rainwater out of the sewers by using sustainable drainage systems. “Which isn’t hard to do,” Chisholm says.

“Then there will be plenty of room in the sewers.” As he points out, it’s a lot less disruptive to plant trees beside streets with drainage around them, than it is to dig up the street and lay new sewers.

The Government has a £5.2 billion fund for flood defences. The challenge for local authorities is getting access to the money. “The mechanisms to get that kind of money are quite involved,” Chisholm says. “Especially when a local authority only needs a small amount of money for a few tree planters around traffic calming measures.”

The solution certainly isn’t more legislation, given that the legislation already in place isn’t being enforced. 

Since 2008, any new driveway more than five square metres in area must provide a drainage system for the water to run to a permeable area. If it doesn’t, then you will need to get planning permission. But, says Chisholm, there are so many loopholes, it’s rarely observed, and local authorities don’t have the resources to make it a priority: “You have to go looking for the guidance of what’s permitted and it’s almost a case of ignorance is bliss.” 

One area of legislation that could have a major impact – if only it were enforced – is the requirement that all new developments have sustainable drainage. House builders have an automatic right to connect the drainage of a new house into the existing sewage network.

The Flood and Water Management Act 2010, passed in the wake of the 2007 floods, made this right conditional on putting sustainable drainage systems in so that it’s just sewage that’s carried, not the rainwater as well. But while this was passed into law, it was never implemented. “It was perceived shortly after that point as too much of a burden for developers when post-recession growth and housing delivery was the main agenda,” says Chisholm. “We’ve had opportunities to deal with this in the past but decisions have been made that haven’t dealt with it.”

With the increasing frequency of sewage pollution events and surface flash flooding, how can we not? While builders might not like change, many of these sustainable drainage systems aren’t complex. 

And there are undoubtedly things we can all do at an individual level. “Just imagine if everyone in London installed a water butt and emptied it when a storm was due, what a difference to surface water flooding that could make,” says Long-Dhonau.

You certainly might want to think twice about what sort of driveway you choose in the future. However, pinning the responsibility for surface flash flooding on individual homeowners won’t work. The remedy “needs to be done at a more strategic level”, says Chisholm. “Asking homeowners to change their driveways is locking the stable door after the horse has bolted.”