The roof of the NEMO Science Museum in Amsterdam is not only an architectural masterpiece, but also a much-loved public space. The striking rooftop square, designed by Renzo Piano, recently underwent an extensive renovation. The reason: persistent leaks and an outdated rainwater system. But the renovation also offered opportunities for renewal. With a greener, future-oriented redesign, Amsterdam gained a fresh city square to mark its 750th anniversary – and at one of the highest points in the city, no less. For the flooring, Accoya wood was deliberately chosen, on account of its sustainability and robustness.
Steyn van Hamersveld, Head of Facilities at the NEMO Science Museum, explains why the renewal was necessary: “The roof had been leaking for over ten years. Because of the complex angle of inclination and the structure with heavy concrete elements, however, the renovation was no easy task. Initially, after repairing the waterproof layers, we wanted to reuse the original concrete blocks. But that offered little added value and remained expensive. So we asked ourselves: if we are going to invest anyway, could we not make the rooftop square more contemporary at the same time?”
Both the museum management and the City of Amsterdam were immediately enthusiastic. With this new layout, we wanted to strengthen the bond with the city and our visitors. After all, NEMO is there for everyone. The square had to invite people to meet and be usable in a multifunctional way.
Sustainability was central to the choice of materials. Steyn: “Renzo Piano brought Accoya wood to our attention, produced at Accsys in Arnhem and supplied by Carpentier. This fast-growing wood is resistant to fungi, rot-free, and has a long service life. I went to see Accsys for myself and was immediately convinced – especially because near our museum there has for years been a Chinese restaurant floating on the water alongside a jetty made of Accoya.” Alongside ecological sustainability, robustness also played a role. “Our roof welcomes hundreds of thousands of visitors every year. Accoya can withstand that load and has a low CO₂ footprint,” says Steyn.
For Jeffry Nuis, project coordinator at contractor Ooijevaar, it was also a first: “For us it was the first time we worked with Accoya, as well as with the concealed clip system for installation. Fortunately, our installation partner did have experience with this. The advantage is that the floor is easy to dismantle, although that will rarely be necessary. What is more, the wood remains untreated, so that it weathers beautifully to grey – exactly as the architect wanted.”
The museum’s location – surrounded by water and above the IJ tunnel – made the site logistically challenging. Jeffry: “We placed a crane on the existing lift shaft. After investigation, this proved to be the best solution. That way we could easily bring materials in and out, with minimal load on the quay.” The old roof layers were completely removed down to the concrete surface. “On top of that we applied insulation again and a bitumen layer as a water barrier.”
“Next we installed the feet for the supporting structure of the new timber decking. Together with a partner, we developed feet of various lengths, each adjustable in height by around 10 centimetres, in order to accommodate the differences in level in the original roof. Between the smallest and largest legs there was no less than 35 cm of difference. On top of these came galvanised steel L-profiles, timber joists, the aluminium clip system and finally the Accoya floor,” Jeffry explains.
Thanks to Ooijevaar’s smart approach, the museum largely remained open. Steyn: “The works took place in winter, when it is quieter. Everything went according to plan. So the impact on visitors was limited.”
Since May 2025, the renewed rooftop square has once again been open to the public. Jeffry: “It has become greener, more inviting and multifunctional. The square is freely accessible, without having to go through the museum. At the bottom of the stairs there is now also a kiosk for snacks and drinks, which enhances the user experience.”
Steyn adds: “The result exceeds our expectations. During the ToekomstTiendaagse (Future Ten Days) in June, we used the square exactly as it was intended: as an open space where all kinds of activities can take place. That worked excellently. In the future we plan to hold more events on the roof.” Finally, maintenance remains important, Steyn stresses: “Just as with the previous concrete floor, regular cleaning is necessary. But we are prepared for that.”
Source: Architectura - author: Joris Hendrickx
