Building within canals is a challenge

"This is a unique project," says Roeland Pullen, consultant roof and facade greenery at idverde NL. There will be roof gardens and roof greenery on four levels at the DNB headquarters. idverde NL is involved in the project as consultant and executor.

"We elaborated the basic specifications and drawing work in technical depth," Pullen explains. "In doing so, we fine-tuned the original plan in terms of technical details, furnishing elements and planting, and contributed ideas on how to optimize the project financially and technically within the framework. This of course includes practical feasibility, long-term quality and facilitating future maintenance."

"When constructing roof gardens on an existing building, you have to take into account the supporting structure, gable connections, roof upstands, water drainage and new or existing roof elements, among other things," Pullen says. "In the case of the roof garden with trees at ground level, for example, it turned out that the basement roof in question was less load-bearing than thought. How can you achieve the same appearance with less weight? We have a lot of experience in that. Working closely together, we always come up with great solutions. We also had a lot of coordination with the contractor and roofer. That is very important in roof gardens with regard to waterproofing and drainage."

idverde NL performs the work within Amsterdam's canal belt. "That makes transport challenging, because heavy truck traffic is not allowed within the canal belt," says Pullen. "That's why we use a hub outside the city, from where we use smaller trucks to transport the material further. Vertical transport with cranes near the building is also trial and error. We blow the substrate for the roof gardens onto the roof with long hoses from a silo truck at some roof sections."

"This project is unique in every possible way," Pullen concludes. "The size, the fact that it is an existing and iconic building, the location in the heart of Amsterdam with the associated challenges of accessibility and logistics, and the multiple levels of roof gardens. From the highest roof garden, at 65 meters, you look out over the entire city. It is a special experience to be able to realize a roof garden there and to work with DNB on greener solutions on their building."