Unique solar retention green roof in the Dutch city of Brunssum combines many advantages

The Sanforum center for health and diagnosis in the Dutch city of Brunssum, which was built mostly during the last year, contains several health and spa features. This modern complex contains everything related to health e.g. doctor's consulting offices, chemist's shop, ergo-, physio- and speech therapy.  It also offers ambulant primary care and subsequent secondary care. Additionally there are informative events, workshops and conferences related to health issues. Furthermore, there are plans for assisted living facilities. The objective of both owners and planners is to create a spa and health center for the region, that thoroughly covers every aspect of these topics. All this should be accomplished by means of a modern building which should be friendly towards visitors and patients, which should also be functional and appealing and blend harmonically into the green surrounding landscape.

Multi-functional use of roofs. Solar-Water retention-Green roof

Already at the planning stages there were special requirements for the use of the 4.000 square meter flat roof:

  • Ecological issues (blending with natural surroundings, biodiversity)
  • Energy generation through photovoltaics
  • Rain water retention

In a project group consisting of planners and system providers, several solutions were analyzed. In the end two existing Optigrün System Solutions were selected, combined and adapted to each other, after consultation with the involved trades. It was clear from the beginning that the roof had to be greened to comply with the ecological issues mentioned above and equipped with photovoltaics .The combination of photovoltaics and roof greening is a long-standing, proven issue, both in Germany and the Netherlands and was implemented by means of the System Solution „Solar Green Roof“. At that, the newly developed photovoltaics supports „Sun Root 15“ with module inclination of 15° were used, so that narrower row spacings were possible. By having more modules per surface, unit the peak power (kWp) increases and the profitability of the system also.  „Sun Root 15“ is a mounting system secured by means of an applied load, which is not only light and easily installed, but can also store 15 liters of rain water per m². „Sun Root“ is  multi-functional: it is permeable and held down by applied loads, increases profitability, retains and drains water. Optigrün's „Solar Green Roof“ is suitable for most of the conventional photovoltaic modules, has been tested for stability and can be used in new constructions or renovations. Optigreen's Engineering Department offers a free service, which consists of planning the mounting system for south and east-west alignments, available for 30° or 15° module inclinations.

Due to the fact that rain water retention demands were larger than those rendered by extensive roof greening, and that there was no room for the planned ground-level storage reservoirs, the roof was used additionally as a retention area. The System Solution „Retention Roof Type Flow Control“ was used in this case. This System Solution was developed years ago and now refined so as to use available retention volumes on roofs and integrate them into the rain water management project.  The basic principle may be explained thus: a water reservoir is created on the roof. On top of this you install either intensive or extensive roof greening or a public roof which may be used by pedestrians or vehicles.  The building block of such a system is the Water Retention Box WRB 85, which in combination with a Flow Control Regulator can store up to 80 liters per square meter. In the Brunssum project the Solar Green Roof was installed over the filter fleece that covers the retention boxes. This Retention Roof is most effective on a 0-pitch roof. The decisive module of the system is the regulator on the roof's drain, whose accumulation level and other parameters may be calculated exactly with the computer simulator program „RWS“. Important factors in this simulation are, among others, local rainfall values and the desired drain patterns. With the „Retention Roof Type Flow Control“ you may adjust the maximal flow up to 1-10 l/s x ha and control its retention time.

Certification according to BREEAM

BREEAM is an internationally recognized certification system that assesses the sustainability of construction projects.  In the case of the Sanforum in Brunssum, the building complex was consciously integrated into the green surroundings and several measures were implemented in favour of the environment as well as animal and plant life. Roof greening was one of these measures. Roof greening not only provides a habitat for many insects, but contributes to cool the building and its surroundings on hot days.


A roof may not contain only greening or only photovoltaics. There are many good reasons to combine photovoltaics, greening and water retention on a given roof:

  • The performance of a photovoltaic system is increased by the processes of evaporation and cooling associated with roof greening, thus contributing to a faster profitability of the project.
  • Solar Green Roofs contribute to improve the energy balance of a building by screening and insulating heat, by reducing energy consumption and COemission, by reducing noise and binding dust as well as toxic substances.
  • Roof greening and retention roofs retain rain water, reduce drainage peaks and unburden the sewer system.
  • As more water is available, plant biodiversity will be greater.
  • Greening also protects roof insulation, so that an operating life of 20-25 years without interim mending or renovation can be achieved.

Additional information regarding the mentioned System Solutions:

www.optigruen.de (Webcode „web244“ and „web509“)


Construction-site billboard at the Zorgplein Sanoforum in Brunssum

Roof area:4.000 m²
Building owner:Zorggroep Sanoforum/Jongen Compaan
Architect:AMA Group Associated Architects
Constructor:Jongen Landgraaf
Roofer:Dakspecialisten Verkoelen Weert
Roof greening:Optigrün-Partnerbetrieb Jonkers Daktuinen, Venlo
Greening system:Optigrün international AG
Solar:Duurstroom/Binksolar Zundert
Fall protectionEurosafe Latchways, Zwolle

Photos and diagrams

Photo 1: Finished Solar-Retention-Green Roof: green, stores a lot of water and provides energy – multi-functional roof usage
Photo 2: Cooling due to evaporation increases performance of the photovoltaic system
Photo 3: Water Retention Box WRB being installed
Photo 4: Mounting photovoltaic supports Sun Root 15
Photo 5: Partial view during installation. Solar Green Roof is installed on top of Retention Roof
Diagram 1: Schematic representation of the build-up in the Solar Retention Green Roof

Photo credits „Optigrün“. Thank you!