The Boomtoren, the newest addition to the Hof van Cartesius, a circular workspace for creative and sustainable entrepreneurs in Utrecht, the Netherlands, is a tower made of 99 per cent reclaimed materials, including recycled CLT and windows from demolished Dudok buildings.

The Boomtoren (Tree Tower) is a proof-of-concept that it is possible to build circularly, including up in the air. The building was designed by Alessandro Zeno (Archifre) and adds 5000 m2 of space to the Hof van Cartesius.

The foundation of the tower is made of glass foam, a material made from recycled glass which cannot be turned in new glass. Glass foam can be completely reused if the building is demolished. Another benefit is that less concrete has to be used. The floors are made of concrete, but to make them more sustainable, cement was mixed with recycled concrete, ensuring that 20 per cent less cement was needed compared to conventional concrete. The concrete had to be left to dry for a longer time (56 days vs. a usual 28 days), but it had a significant lower carbon footprint than if conventional concrete was used. You can learn more about the foundation and flooring in the video below (in Dutch).

The tower of four stories is made mostly out of wood, CLT (Cross Laminated Timber) to be exact. The material was reclaimed from a demolished school in Rotterdam and offers a good alternative from concrete and steel. The doors and windows, including solar screens, are from a housing renovation. The window in the façade was reclaimed from a post-war garage designed by Dudok that had to make way for housing.

The façade is partly clad in yellow signs of the Dutch railway operator NS, which shows the train timetables. Railway tracks are also used in the design, as well as parts of the platform of station Maarn, which were used in the pavement and foundation.

The side façade is clad with wooden mosaic tiles, offering shelter to insects, birds and bats. The tiles are made from waste wood from the construction process and were in part designed by engineering students.

The Boomtoren owes its name to an oak tree and willow tree that were already on the lot. Rather than being cut down, the trees remained where they were, proving that it is possible to build nature inclusively.

In the interior, old consoles of the air traffic control base in Soesterberg are reused.

https://www.youtube.com/watch?v=t2SaoLZAPew

Photos: Inez Faber