Cooling cities

Greening buildings has been a niche topic in the real estate sector to date, but that is now changing. Greening of roofs and façades is increasingly gaining ground as a strategy for adapting to climate change. Innovative real estate projects highlight the potential. By Dagmar Hotze

Mention green buildings to people and many will think of old buildings swathed in ivy or courtyard walls half hidden by masses of straggling vegetation. In Germany, the 1980s saw the advent of numerous ideas to visually upgrade urban concrete jungles by adding as much “biomass” as possible. 

Today, green roofs and façades serve a much broader purpose. As elements of the climate adaptation strategy of many cities, they are being used to avoid sealed surfaces and improve the local microclimate. At the same time, they are designed to absorb and retain rainwater with delayed runoff and provide replacement habitats for flora and fauna.

Developers and investors discover the power of nature

Their positive environmental impact is considerable. According to German trade association Bundesverband Gebäudegrün (BuGG), one square metre of easy-care green roof can store 30 litres of water, reduce the air temperature by 1.5 degrees Celsius, absorb 800 grammes of CO2 and reduce noise levels by 20 decibels. A green façade yields similarly good results. Developers and investors are increasingly harnessing this power of nature to create sustainable properties.

One example is the prominently situated, part new and part heritage-protected Calwer Passage complex in Stuttgart, which was designed by Ingenhoven Associates. The 27-metre-high and 133-metre-long seven-storey building is home to a mixed mini-forest of 40 trees on the roof, while the street-facing façades feature 11,000 plants in 2,000 continuous troughs that run the whole length of the upper floors. A digital supply system is used to ensure the green façade is amply provided with water and nutrients. Depending on the season, foliage and flowers erupt all over the building, attracting an abundance of insect and bird life – to the delight of the tenant, law firm CMS.

Inner-city greening has a really positive impact, especially in climatically challenging conditions like those presented by Stuttgart’s location in a basin.
Florian Starz engineer at Werner Sobek Group

“Inner-city greening has a really positive impact, especially in climatically challenging conditions like those presented by Stuttgart’s location in a basin,” says Florian Starz, an engineer at Werner Sobek Group who was involved in designing the façade. The layer of foliage that shields the façade significantly reduces the surface temperature through shading and evaporative cooling, thereby minimising the heat island effect, with up to 50 percent of the incident solar radiation being used for water evaporation. 

The Eden Tower under construction at the entrance to Frankfurt’s ­Europaviertel district, financed by Belgian investor Immobel, is another eye-catching green project. The vertical ecosystem of the 98-metre-high residential building, which was designed by Helmut Jahn and won the bronze FIABCI World Prix d‘Excellence Award in 2022, consists of 200,000 robust plants that wind their way up 28 storeys and add green life to 263 apartments. 

The 14-storey Canyon building, created by CV Real Estate in Frankfurt’s banking district and based on plans by architects KSP Engel, is also something of a trailblazer, offering flexible office space and artists’ studios plus restaurants and retail facilities across some 38,000 square metres of floor space. LEED Platinum certification is being sought for the building, with highlights including the striking greening of its façade with ferns, grasses, perennial shrubs and climbing plants. With the assistance of a special trellis, they snake their way over two, and in some places three, storeys. Multiple greened roof areas are also accessible by the tenants. These areas absorb up to 2,000 kilogrammes of CO2 a year and reduce nitrogen levels by up to 40 percent. 

As an added bonus, the nature-inspired design of the building contributes to energy savings of around 10 percent and reduces particulate matter pollution by up to 30 percent. “Permanent and sustainable greening would be impossible here without the considerable amount of substrate and insulation of the troughs, which significantly reduces plant death caused by frost damage,” explains Horst Robert Schinschke, Deputy Director at KSP Engel. “It’s also advisable to avoid monocultures in order to head off the risk of losing all the plants in the event of a pest infestation,” adds Caspar Schmitz-Morkramer, Managing Director of Caspar architects, which designed the Cannion new build in Stuttgart’s Neckarpark for Fay Projects. Featuring a green façade, the 27,000-square-metre complex consists of offices, a hotel and other facilities. A DGNB Gold certificate and an equivalent WiredScore label will be sought. Greening taxonomy-aligned new builds can only be a start, though.

Greening new builds and transformed properties

When it comes to retrogreening the façades of properties undergoing transformation, Drees & Sommer relies on a nonwoven solution from Vertiko, which is showcased on the company’s OWP12 headquarters building. The green façade extends over an area of 100 square metres, taking in three storeys with a total height of twelve metres. A wall-mounted nonwoven substrate system is used, more than 95 percent of which consists of glass and basalt composite. “­Nonwovens as a material are important to meet the strict fire protection requirements in building construction,” says Daniel Hof, a green façades expert at Drees & Sommer, adding that it was also easy to install the comparatively lightweight panels over finished façades. 

From a global perspective, trade body BuGG sees Germany as a frontrunner when it comes to roof greening. But there is still much room for improvement. The revision of the EU Buildings Directive, which makes the creation of green infrastructures mandatory for new buildings and buildings undergoing major renovation, could accelerate building greening. It is set to be adopted by the European Parliament in late 2023. As such, it is high time for developers, real estate investors and building owners to engage with this important issue.

Greening the Canyon is aimed at making the building itself look like a canyon.  The design that architects KSP Engel came up with features horizontal and vertical plantings at different levels. The project will be constructed by CV Real Estate at Mainzer Landstraße 23 in Frankfurt am Main by the end of 2026.

Some local authorities and a number of German federal states offer direct funding for building greening. There are also nationwide funding programmes, such as the Federal Grant Programme for Efficient Buildings and funding for serial refurbishment, which include greening of buildings as an eligible measure. Urban development programmes are also subsidising green roofs and façades as elements of green infrastructure. 

By Dagmar Hotze

Title image: Bloomimages

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