Urban Nature: Green Facades

Green facades generate a “breathing urban space” and promote biodiversity in urban areas. The plants bind CO2 and clean the air. Greening improves the microclimate of sealed and overheated urban spaces. For building owners and users, green facades also offer noise reduction and visual protection. The plants provide shade and sun protection as well as lowering the ambient temperatures. The rainwater retention provided by green façades is also important – not only because of the increasingly frequent heavy rainfall events.

Green façades offer significant added value, but also lead to slightly higher investment costs, additional costs for care and maintenance and (depending on the design) possibly additional loads for the supporting structure. Special features in the planning phases include requirements from the greening itself, such as fire protection, integration of supply technology, frost and heat protection, and height access for maintenance and care by gardeners. Using three selected project examples, the following will explain in more detail what the special features are in the planning and realisation of green facades and how they can be taken into account appropriately.

Calwer Passage, Stuttgart/Germany

The new building of the Calwer Passage in Stuttgart has a length of more than 130 metres and, in addition to office use on the upper floors, also accommodates flats as well as areas for retail and gastronomy. On the façade sides facing the street, intensively greened strips are created along the upper floors as well as roof gardens. The façade greening consists of a load-bearing horizontal steel substructure along the opaque brushing strips, which serves to accommodate the pre-cultivated plants in inner troughs. These green strips are arranged one above the other on each storey and connected to each other with vertical climbing aids in front of the glazed surfaces. It is therefore not a small-scale vertical greening along a wall surface, but a construction in front of the building with planters of considerable size.

The large trees on the Calwer Passage already reached heights of up to 10 m and weighed up to 7 t when they were installed in May 2021. Later, they are to reach crown heights of up to 15 m.

The irrigation and drainage of the approximately 2000 planters is integrated into this construction, which also provides access for the gardeners, for example for the care and pruning of the plants. The green facades are complemented by the intensive greening of the roofs using a wide variety of shrubs and large tree species. The planters themselves release excess water downwards through openings. From there, it is drained off and collected in a controlled manner.

An additional irrigation system is used to supply the plants; monitoring is carried out, among other things, via humidity and temperature sensors installed at selected points within the façades. The system can be operated fully automatically, but is of course also monitored by experienced gardeners. The plants that will be used on the façade were cultivated before the construction of the shell began, so that they would have reached a certain size and robustness by the time they were used in Stuttgart.

KII, Düsseldorf/Germany

The trapezoidal, six-storey office and commercial building, together with the “food court” opposite, forms a green urban ensemble. The building is planted with over 30,000 hornbeams – an absolute novelty in Europe. The hedges are set in a kind of trough-in-trough system. The rows of troughs are staggered in such a way that a natural supply of sunlight and rainwater to the plants is guaranteed. To ensure adequate height access for pruning and maintenance of the plants in the façade, maintenance walkways and safety systems for the gardeners have been installed. In places where there was no space for maintenance walkways, a drive-on system was installed along the trough rows.

Design sketch for the supporting structure of the trough system at KII.

In order to keep the number of penetrations of the insulated building envelope as low as possible, a special substructure with intermediate beams in the insulation level was developed for the green façade. A sheet metal cladding above the insulation and sealing layer acts as weather protection and allows fallen leaves and branches to slide down as if on a large slide. On the ground floor, green waste is collected in large-volume gutters and removed by the landscape gardeners.

The hedges were pre-cultivated over a long period of time in a tree nursery and delivered to Düsseldorf for installation in the interior troughs. The façade structures include supply systems for irrigation, fertiliser application and drainage. The installed technology regulates itself in part automatically on the basis of information on humidity, temperature, etc. provided by sensors distributed across the façade. In addition, the façade is inspected and maintained at regular intervals by experienced gardeners.

Q20, Stuttgart/Germany

In the course of the urban district development of Stuttgart’s Neckar Park, a new residential and commercial area is to be built on a total area of approx. 25 hectares. The Q20 ensemble consists of three above-ground, non-orthogonal building sections and a shared underground car park. The green facades and roofs, especially those facing the publicly accessible courtyard of the three buildings, are intended to form a “green valley”. The buildings taper towards the top in this area, thus enabling optimised use of daylight while at the same time implementing the municipally required green component in the façade through large-volume plant troughs. The use of rainwater through retention bodies rounds off the sustainable neighbourhood development.

Greening with large-format, pre-cultivated plants is much more demanding in terms of construction than a soil-bound system. In order to limit the effort required for the substructure, Q20 mainly aims to transfer the load for the plant troughs of the green façades through the building’s supporting structure itself.

The partly cascade-shaped arrangement accommodates this; to secure the troughs behind the curtain-type rear-ventilated façade in the parapet strips, they are only secured in position. In addition to the planted troughs, components of the greening at Q20 will include climbing aids, supply systems with sensors for monitoring and drainage. Similar to the Calwer Passage, the plants will be selected from a variety of different species.

Would you like to hear more about the importance of green facades and their engineering? Do take a look at the following videos on our YouTube channel, as well – it’s certainly worth it. In the first video, managing director Roland Bechmann speaks about the ecological and the functional importance of green facades.

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In the second video, facade team manager Florian Starz explains how he helped engineer some of the world’s largest green facades.

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