Delay up to 24 hours
Bluegreen roofs store rainwater and delay runoff for up to 24 hours, reducing sewer overload.
Bluegreen roofs for smarter water storage
Extreme rainfall is a growing challenge. Sempergreen bluegreen roofs capture, store and gradually release rainwater, reducing sewer overload. At the same time, they boost biodiversity, cooling and aesthetics in cities.
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How bluegreen roofs work
Climate change leads to heavier and more unpredictable rainfall, often overwhelming city drainage systems. Streets flood, infrastructure suffers damage and urban liveability decreases. The solution? Manage rainwater where it first falls: on the roof.
Sempergreen’s bluegreen roofs combine water storage with greenery, turning unused surfaces into climate buffers.
Meets local regulations
All systems comply with local stormwater bylaws and water policies, making approval and subsidy applications easier.
For roofs over 50 m²
Bluegreen roofs are designed for larger roofs from 50 m², with tailored calculations and project-specific advice.
There are two types of systems: Purple-Roof, a lightweight solution for sloped roofs and renovation projects, and Bluegreen Roof, a robust system for flat, load-bearing roofs, typically used in new builds. Both designs temporarily store rainwater and release it gradually, reducing peak loads on sewers and lowering runoff coefficients. At the same time, evapotranspiration from plants cools the city, while sedum and biodiversity planting boost nature in dense urban areas.
With bluegreen roofs, water challenges become water opportunities. Every roof becomes a contributor to a greener and healthier city.
FIND THE PERFECT BLUEGREEN ROOF FOR YOUR PROJECT
Feeling a bit flooded with ideas? Don’t worry! We’ll help you find the right solution for your project. With just a few quick questions we’ll help you find the right approach and system for your project. You’ll receive customised advice to make green work for you.
Purple-Roof
Purple-Roof is the ideal solution for existing buildings and renovation projects. The system is lightweight and can even be applied on roofs with a slope of up to 5°. Its build-up consists of a detention layer, a storage layer, a substrate roll and a Sedum mix blanket. Thanks to the detention layer, rainwater discharge is slowed down through friction. Runoff can be delayed by up to 24 hours, significantly reducing peak loads on sewer systems.
Because of its low weight, Purple-Roof is perfect for buildings that cannot support heavy constructions. At the same time, it offers multiple benefits: it reduces the runoff coefficient, enhances biodiversity, and contributes to cooling and aesthetics. For multifunctional use, the system can be combined with our lightweight vertical solar panels. This way, any existing roof can be transformed into a sustainable, climate-resilient solution.
- Urban Greening
- SemperGreenwall Outdoor
Healthcare architecture rooted in nature
- Biodiversity Boost
- SemperGreenwall Outdoor
A green welcome at BMW Group Dingolfing
- Urban Greening
- SemperGreenwall Outdoor
A green pioneer for over a decade
"Quote nog in te vullen"
Bluegreen Roof
Bluegreen Roof, Sempergreen’s roof system, is designed for flat, load-bearing roofs and is often used in new construction projects. Instead of traditional drainage, this system uses water retention crates. These crates temporarily store large volumes of rainwater, which is then gradually discharged or evaporated through the vegetation.
The retention roof can be tailored to the specific water challenge of each project, as both the type of crate and the required storage capacity are flexible. With its very low runoff coefficient, Bluegreen Roof provides optimal performance in urban water management. The system can be covered with Sedum blankets, a mix of nectar and host plants, or a combination of both. Biodiversity packages and solar panels can also be added. In addition, either static or dynamic (smart) outlets can be installed to control the speed and timing of discharge. This makes water management more effective and future-proof.
When to choose a Bluegreen or Purple-Roof?
Choose Purple-Roof if:
- You’re working on an existing building
- The roof has a slope of up to 5°
- A lightweight solution is required
- You need temporary water storage and delay up to 24 hours
- You want the option to combine with lightweight vertical solar panels
Choose Bluegreen Roof if:
- You’re developing a new construction project
- The roof is flat (0°) and load-bearing
- You need large-scale water storage capacity
- You want to add biodiversity packages, Sedum mix or solar panels
- You value static or dynamic (smart) outlet control for discharge timing
Smarter together: Sempergreen × Wavin
Green roofs meet smart water management. Sempergreen and Wavin combine their expertise to create integrated blue-green systems that store, filter and slowly release rainwater. By connecting Sempergreen’s green roof layers with Wavin’s advanced retention and drainage solutions, cities become more resilient to heat and heavy rainfall.
This partnership turns rooftops into living sponges, capturing water when it’s abundant and reusing it when it’s needed most. Together we shape the cities of tomorrow, one drop at a time.
Smarter together: Sempergreen × Purple-Roof
Science meets stormwater resilience. As one of the founding contributors to the Purple-Roof research consortium, Sempergreen helped develop a scientifically proven green roof concept that doesn’t just retain water, but detain it.
The Purple-Roof Concept, born from years of research at Green Roof Diagnostics in Virginia, uses a unique friction-based drainage layer to temporarily hold rainwater and release it slowly, even during extreme storms. This proven innovation turns rooftops into active water buffers that protect cities from flooding and urban heat. A lightweight, data-driven solution that keeps both people and nature in balance, turning every roof into a living buffer for a climate-proof urban future.
Replanting the planet together
Explore more smart green roof systems for energy, nature and water
Our green roof systems transform rooftops into climate solutions. They retain rainwater, cool cities, enhance biodiversity and even boost solar performance. Each system is carefully engineered for durability and designed to make every square meter count for people and the planet.
See how this works for your project!
Joris Balvers
Questions about our bluegreen roofs
Curious about our bluegreen roofs? Here you’ll find the most frequently asked questions. Want to know more? Contact us directly with one click.
Can green roofs prevent flooding?
Green roofs contribute to flood prevention and mitigation by absorbing and buffering stormwater. Depending on the amount of water storage needed within your project and the roof construction, you can choose between a regular green roof, a Detention Roof, or a Retention Roof.
Does a green roof buffer water?
Yes, every green roof absorbs and buffers water. The best green roof for your project depends on the amount of water storage required and the roof construction. Sempergreen offers two green-blue roofs for storing or buffering large amounts of rainwater during peak rainfall: the Detention Roof and the Retention Roof.
How much water can a green roof retain?
The exact performance is always calculated project-specifically, based on roof design, load capacity, and local rainfall patterns. An extensive green roof can typically retain 25 to 45 litres of water per m², depending on the build-up and substrate depth.
With advanced systems such as retention or detention roofs, designed for water buffering or delayed drainage, water storage can be significantly higher. In these systems, runoff delay can extend up to 24 hours or longer, reducing peak loads on urban sewer systems and helping prevent flooding.
How much runoff does a green roof have compared to a conventional roof?
A conventional roof drains almost all rainwater immediately, with a runoff coefficient of around 0.9 to 1.0 in urban environments. This means nearly all rainfall flows directly into the sewer. In contrast, an extensive green roof has an average runoff coefficient of 0.5 to 0.7. This indicates that 50 to 70 percent of the rainfall is drained, while the rest is temporarily retained in the vegetation, substrate, and drainage layers. By buffering and delaying runoff, a green roof helps reduce peak loads on sewer systems and lowers the risk of flooding during heavy rain events.
How does a water-retaining green roof project with a retention roof or detention roof work?
Sempergreen’s blue-green roofs are suitable for larger roofs, starting at 50 m2. For new construction projects, there is the Retention Roof, and roofs of existing construction and renovation projects can be made water-retaining with a Detention Roof. The installation is similar to that of other Sempergreen green roof systems. If the roof is larger than 50 m2, we offer you the option of requesting a water calculation. Based on this calculation, we can determine exactly what the Detention or Retention Roof can do for your project.