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Dutch flower bulb company gets fast and energy-efficient roof renovation

Dutch flower bulb company Royal De Ree Holland had plans to renovate their roof for some time, but the decision to install a photovoltaic system accelerated the project. The renovation involved their two locations in Lisserbroek (North Holland). From March to July 2019, a total of 33,000 m² of roof surface was insulated, covered with Elevate’s RubberGard EPDM waterproofing membrane and equipped with 11,000 m² of solar panels.

Project ID

Lisserbroek, The Netherlands


PV roofs

Project type


Building type

Industrial building


33,000 m²


Elevate RubberGard EPDM 1.5 mm


Fully adhered

Flower bulbs are treated in air-conditioned halls, so moisture infiltration and lack of proper insulation can have a harmful impact. A few years ago, there was a collapse on the roof due to water accumulation. In order to avoid a new collapse and following the decision to install solar panels, an assessment of the entire roof was carried out. The report showed that additional measures were needed almost everywhere, such as installing extra slope insulation, drains, scuppers, and the creation of compartments on the roof.

"You definitely want a roofing membrane with proven durability under solar panels" says Jaco Rip from the J. Rip Plumbing and Maintenance Company, whose company acted as a cooperating contractor during the project. "RubberGard EPDM has high resistance to ozone, UV radiation and extreme temperatures. It is easy to install and is available in large seamless panels, resulting in fewer seams and shorter installation time. Because of the positive experiences with the material and the supplier, we opted for this roofing system from Elevate."

The original roof was insulated with mineral wool and covered with a bituminous waterproofing membrane. The new roofing system was installed directly over the old one. After cleaning and drying the original roof covering, two layers of PIR insulation boards were mechanically attached to the substrate, except for a part where the roof deck consisted of wood wool cement. In this section, the insulation was adhered with Elevate I.S.O. Twin Pack insulation adhesive because it was not possible to screw into this support. Elevate’s RubberGard EPDM 1.5 mm thick roofing membrane was fully adhered on top of the new layer of insulation.

Because of the project scope, the time constraints and previous positive experiences, Elevate Master Contractor Lukasse Dakbedekkingen was engaged to carry out the installation during the quiet period in the production of flower bulbs before the summer. The deadline of July 1, when high season starts, had to be respected. Thanks to good work preparation and teamwork, up to 2000 m² of roof surface were completed per week. The contractor worked with RubberGard EPDM rolls of 5 m wide by 30 m long. They also used the SuperSpreader, which further sped up installation time to adhere the EPDM membrane. Seams were sealed with Elevate’s self-adhesive QuickSeam Splice Tape.

"Little can be seen of the roofing now, but we are proud of it," says Bram Lukasse from Lukasse Dakbedekkingen. "The project was located not far from the coast and the wind sometimes bothered us during installation, but everything went smoothly in the end. This is largely due to the good follow-up and project management of Elevate, who guided us on site every week. It was very pleasant working together. The schedule was met even slightly earlier than expected," he added. "It was a great project, a great reference. We hope to be able to make one like this every year."

The solar panels, which are expected to last for 25 to 30 years, were ballasted in place with tiles. The energy supplied is for the flower bulb company's own use, which wants to use it as CO2-neutral source.

This project was nominated for the "Roof of the Year 2019" (Dak Van Het Jaar) award organized by Dutch magazine Roofs. The winners will be announced on 25 September 2020.