First Dutch Detention Roof at Vrumona against urban flooding

At soft drink supplier Vrumona’s headquarters in Bunnik, the Netherlands, the first Detention Roof has been realised. An innovative blue-green system that captures, stores and slowly releases rainwater. Developed by Sempergreen together with Green Business Club Bunnik, it marks a milestone in climate-resilient urban design.

Multifunctional surface

Every part of the roof contributes. Rainwater is buffered and nature is given room to grow.

Climate adaptive design

The roof stores water during heavy rainfall and helps cool the surroundings during summer heat.

Biodiversity in the built environment

A diverse planting plan attracts pollinators, birds and native insects. This turns the roof into a thriving ecosystem.

Innovative blue-green roof concept against flooding

In October 2021, the first Detention Roof in the Netherlands was installed at soft drink producer Vrumona’s site in Bunnik, the result of a powerful local collaboration within Green Business Club Bunnik. The 588 m² roof combines vegetation, water buffering and smart drainage technology to drastically reduce the risk of flooding during extreme rainfall. Officially opened by Councillor Jocko Rensen, the project demonstrates how business, government and innovation can work together toward a climate-proof future.

A living water buffer on the roof

Unlike traditional roofs, which discharge rainwater immediately into the sewer system, the Detention Roof temporarily retains it in multiple layers before slowly releasing it. Even when fully saturated, the system delays runoff by up to 24 hours, preventing sewer overloads and reducing the risk of flooded streets. This Sempergreen system also meets the increasingly strict water-management requirements set by Dutch municipalities and water boards.

"This green roof is a wonderful example of local cooperation. It fits perfectly with the circular and sustainable mission we pursue within Vrumona."

Built in just two days

The installation was completed in collaboration with Van Doorn Roofing Specialist and De Dakdokters, who installed the Detention Roof across two roof sections within just two days. The pre-grown Sedum roof system from Sempergreen ensured an instantly green result. Despite being lightweight and modular, the system is robust and suitable for roofs with a pitch of up to 2°, making it ideal for both renovations and new-builds.

Nature’s own water engineer

The Sedum vegetation plays a vital role in the system. These hardy plants withstand extreme weather and provide natural cooling, air purification and CO₂ absorption. The result is a living roof that keeps the building cooler in summer, extends the lifespan of the waterproofing layer and supports biodiversity in the urban environment.

Circular design, local roots

Vrumona’s sustainability mission focuses on circular production and responsible water use, values that perfectly align with the Detention Roof philosophy. Both Vrumona and Sempergreen are active members of Green Business Club Bunnik, a local network of companies and public partners dedicated to making the Spoorzone area more sustainable. This shared ambition created the ideal breeding ground for innovation at the heart of the Utrecht region.

An advanced system structure

The Detention Roof is made up of four carefully engineered layers:

Sempergreen Sedum-mix blanket – a pre-cultivated vegetation layer with 6–8 Sedum species.
Substrate Roll – a water-absorbing layer that also serves as the plants’ growth medium.
Sempergreen storage layer HC40/60 – a honeycomb structure that acts as a temporary water column.
Sempergreen detention layer T5 – the unique slowing layer that uses capillary tension to push water upward, delaying drainage for up to 24 hours.

This intelligent construction ensures effective water buffering even during the heaviest storms, a proven innovation born from scientific research within the Purple-Roof Concept.

Sustainable detailing with peach stones

Even the roof’s edge finish reflects circular thinking: the border is made from peach stones supplied by Nocciolo, a residual by-product that doesn’t rot, mould or absorb moisture. With a lifespan of over 30 years, it’s a durable and aesthetic alternative to traditional gravel.

A blueprint for future-proof business parks

By integrating the Detention Roof, Vrumona and Sempergreen have set an inspiring example for other companies in the region. The project shows that climate adaptation can go hand in hand with innovation and collaboration. As part of the Green Business Club network, this initiative contributes to a more resilient and sustainable Spoorzone; one roof, one storm, one project at a time.

Vrumona’s new Detention Roof was officially opened on 8 November, 2021 with (from left to right) Jocko Rensen (Councillor Bunnik), Evelien Sanders – de Boer (General Director Vrumona) and Stephan Beerends (Sempergreen).

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