A third of garden owners do not realise that paving over green spaces increases the risk of flooding, research reveals.
According to a study commissioned by insurance company Flood Re, a third of British garden owners are unaware that paving and other hard surfaces increase flood risk. In a paved garden, even modest rainfall can generate “bathtub loads of water” pouring into local drains, overwhelming systems and triggering local flooding incidents.
As heavier rainfall becomes more common in the UK, drainage systems are struggling to process the increased volume of water, causing surface water flooding. This can occur anywhere in the country, even at the top of a hill.
Green spaces containing soil and vegetation absorb rainwater and prevent it from channelling into drainage systems. Hard surfacing increases rainwater runoff and places pressure on drainage, making it more likely that homes will flood.
“Intense rainfall alone doesn’t cause flooding – it’s all about what happens to rain when it hits the ground,” says Dr Peter Melville-Shreeve, associate professor at the University of Exeter. “Hard surfaces like our driveways and rooftops disrupt the natural hydrological cycle and stop water soaking in. As we pave over our green spaces – a process we call ‘urban creep’ – more rainwater rushes straight into our sewers. Multiply that across a street and even modest rainfall can contribute to downstream flooding.”
On a 20-square-metre paved garden, even 5mm of rainfall can generate around 100 litres of runoff – equivalent to a full bathtub of water being sent straight into local drains rather than soaking into the ground.
Many homeowners choose to pave over their green spaces, preferring hard surfaces for easier maintenance or converting front gardens into hardstanding parking spaces.
“There’s a real risk that households are sleepwalking into a flooding problem without realising it,” says Kelly Ostler-Coyle of Flood Re.
“Hard surfaces send water racing into drains, but greener, more permeable designs help slow, store and absorb it.”
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The Centre for Water Systems at the University of Essex has been researching methods used by cities around the world to address the challenges of surface water flooding. The most effective approach is to prevent excess water from entering the system by ensuring it is absorbed and slowed down by gardens and green spaces.
“Slowing water down at source – in green spaces, gardens and around homes – can be one of the simplest and most effective ways to manage rainwater and reduce downstream flood risk,” says Dr Melville-Shreeve.
To raise awareness, Flood Re is presenting its “Contain the Rain” garden at this year’s Chelsea Flower Show. Designed by John Howlett and imagined as an urban retreat, the garden demonstrates simple, affordable steps gardeners can take to reduce risk. It features hexagonal planters, water storage and permeable surfaces to create a tranquil, cool space that manages excess rainwater.
Garden designer John Howlett says: “This garden is about showing that you don’t have to choose between beauty and resilience. By using planting, permeable materials and thoughtful design, you can create a space that looks great but also works much harder when it rains. It’s about turning gardens into places that don’t just shed water, but actually help manage it.”
The RHS Chelsea Flower Show runs from 19-23 May 2026.
