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Su DS rainwater

What are Sustainable Drainage Systems?

When open ground is built upon or paved over with a non-permeable surface, such as traditional paving, the surface water due to natural precipitation accumulates. Previously, this rainwater may have been directed into a drainage system where it would eventually be treated at the water treatment plant. This is no longer sustainable for several reasons, such as placing an unnecessary burden on these treatment plants and wasting valuable resources cleaning what is already relatively clean water.

Sustainable Urban Drainage Systems (SuDS) aim to manage stormwater in ways that are closer to nature, with one of the benefits being flood risk management. SuDS generally involves allowing collected surface water to filtrate back into the ground as close to where it fell, allowing it to return to the natural water cycle.

Climate Change is also impacting ever more heavily on our environment. Strategies for dealing with surface water are having to adopt new methods that closely mimic the natural environment. This includes slowly returning the surface water to the hydrological cycle and consequently reducing the impact of human development in the built environment.

At a residential level, strategies include greater use of soakaways and the creation of rain gardens and swales. For areas that need to be covered with some form of surfacing, the use of permeable or porous materials or systems is now strongly preferred.

Antique Oak Millboard Su DS
Su DS rainwater 2
The use of Millboard decking is fully in line with the core principles of SuDS

Where does Millboard Decking fit with SuDS?

A properly constructed Millboard deck, constructed over open ground provides a safe, secure and permeable surface that will not place any additional burden on the existing local drainage system. It can return surface water to the ground more-or-less where it lands, a SuDS strategy known as Source Control – dealing with the water where it arises.

A Millboard deck constructed with small gaps between each board results in rain initially collecting on the surface of the board and then passing through the gaps without impediment. Rainwater then returns to the open ground beneath the deck structure, just as it would have if there were no surface present.

The use of Millboard decking is therefore fully in line with the core principles of SuDS. No surface water is sent into a drainage system; it’s returned ‘at source’ with no additional, unnecessary structures; it has minimal impact on the immediate environment and can support biodiversity, plus no toxic chemicals such as wood stain are needed to maintain it. Thanks to Millboard’s decking longevity, there is also no wasted energy spent producing replacement decks every few years, unlike the softwood options available on the market. Finally, should a Millboard deck need to be fitted over an impermeable surface, the use of a soakaway or a rain garden can be considered.

For more information on SuDS, visit

With thanks to Tony McCormack, Hard Landscape Consultant for his input in this article.

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