Carré Belge Cologne: A Forest in the Sky

In the heart of Cologne, the Capitol, an historic 1920s movie theatre, has been converted into a stylish design hotel and retail complex by Ingenhoven architects and project developer and investor Proximus Real Estate AG. The name Carré Belge comes both from the location near the city’s Belgian Quarter and from the new façade – a distinctive chequerboard of square forms – alternating concrete with window-like open spaces. Enea Landscape Architecture was commissioned to transform the property into a green lung in the city and to design a verdant, varied, yet harmonious urban garden that unifies the complex. The landscape architects did so by creating a playful and dynamic ‘floating forest’, planting trees in the square openings of all six floors of the new façade, including on the green roofs and in the inner courtyard.

A detailed, site-specific study was carried out, including the climate, wind and shadow conditions. This analysis provided valuable insights which trees and native plants could be selected. The distinctive landscape design on the facades features mature trees of various heights and species to create visual interest. Apart from considerations of the site conditions and constraints of planting on upper levels, the trees were chosen to be in harmony with the seasons all year round. For example, the cherry trees like the bride fuji cherry (Prunus incisa ‘The Bride’) and Amanogawa Japanese flowering cherry (Prunus ser. ‘Amanogawa’) bloom at staggered times in the spring, and the deciduous trees turn into a palette of yellows, oranges and reds in autumn. Evergreens such as Scots pines (Pinus sylvestris), blue star juniper (Juniperus squamata ‘Blue Star’) and English yew (Taxus baccata ‘Repandens’) give winter appeal, as well as the choice of trees with a distinctive bark like the Doorenbos Himalayan birch (Betulus utilis ‘Doorenbos’), hornbeam (Carpinus betulus) and ironwood (Parrotia persica).

Enea’s engineering expertise enabled the landscape architecture firm to both design and build this innovative vertical garden. In order to plant large, heavy, mature trees in the sky, so to speak, on concrete buildings, Enea designed special planters, in coordination with the architects. They attached these to all six floors of the facades, as well as on the roof, to ensure the trees had enough soil depth to grow and that the load requirements of the planters and trees were taken into account in the construction of the building. In addition, Enea anchored the trees to the planters to ensure they do not blow over in strong winds.

As Enea are tree specialists, who believe in the importance of planting trees in urban contexts, in order to create shade, lower building temperatures (and therefore energy consumption in summer), promote biodiversity and clean the air, at Carré Belge they planted a selection of what they term climate resilient trees. These are particularly robust tree species that, for example, tolerate severe frost, drought and heat well and can survive weather extremes, such as storms or strongly fluctuating temperatures. In the city, it is also important that the trees planted there are “suitable for the urban climate”. Depending on their location, they must also be able to cope with higher levels of air pollution, often small root spaces with low humus contents, limited sunlight, and sometimes high salt concentrations in the soil due to winter maintenance.

With this project Enea demonstrates that even in an urban context with limited space and depth of soil, it is still possible to create a lush green environment with trees and understory planting. Focusing on sustainability, this “forest in the sky” and the large proportion of green areas throughout the site contribute to improving the urban climate of Cologne.