Climate change is intensifying weather extremes, cities are overheating, and scientists are looking for a solution that will be long-term and sustainable. The thesis of Jan Vystrčil from the Institute of Civil Engineering, Faculty of Civil Engineering, Brno University of Technology, under the supervision of Karel Šuhajda, investigates vegetated facades as a solution for a better urban microclimate, with an emphasis on their behaviour during hot summer weather. The work is part of a long-term extensive research, which the scientists from FAST BUT have been working on comprehensively since 2015.

The climate challenge up close

Research into the impact of green facades on buildings and their immediate surroundings has become more urgent in recent years. "I was interested not only in the immediate effect, but also in how the façade behaves throughout the day, how it reacts to temperature fluctuations and what kind of thermal microclimate it creates in the building's surroundings," says Jan Vystrčil. Observations included monitoring humidity, temperature, water consumption or changes in the weight of the substrate caused by water consumption and vegetation growth. The results of the research confirmed that the greenery on the external walls does indeed "air-condition" not only the buildings themselves, but also their surroundings, and contributes to a higher quality of environment in built-up areas.

Facades as green air conditioning

Vegetated facades, i.e. vertical surfaces covered with plants, are not just an aesthetic addition to modern architecture. According to Vystrčil, they are an effective tool to counter the phenomenon of urban heat islands (UHI) and reduce heat stress. Heat islands are created by the accumulation of solar radiation in solid urban surfaces, which leads to an increase in the air temperature in the urban environment by up to tens of degrees Celsius compared to the surrounding landscape. While conventional façade materials such as ceramics, wood or HPL panels enhance this accumulation, green façades actively cool their surroundings through evapotranspiration. The plants in them act as natural "coolers". In addition, they consume energy when evaporating water, thus lowering the temperature of their surroundings even further. According to long-term research, greenery on facades can reduce the surface temperature of a building by up to 14.5 °C.

Various systems are currently being used for greening buildings: climbing plants planted in the ground or in boxes climbing up the wall, selected plant species placed in containers or panels fixed to the wall or a pre-set structure. Most of the plants used for vertical green walls are commonly available unpretentious perennials, such as cacti, stonecrops, bergenias, dye plants or American cowslip with attractive red leaves.

Directly at the Faculty of Civil Engineering, researchers have previously developed a modular system of panels created by 3D printing. Manufactured from recycled or composite material, other advantages are low weight, high durability and customisation to a specific solution, which includes not only the design but also the ability to integrate different elements directly into the structure.

Experimental research and digital twin

In addition to reducing the temperature directly on the building, the research also showed a reduction in average daily air temperatures in the immediate vicinity of the façade of more than 5 °C. On some days, the difference in maximum temperatures reached more than 11 °C.

To refine the results of the experiment, Vystrčil also used computer simulation to create an accurate digital model of the facade under study. The Envi-met software allows the modelling of temperature, humidity and airflow behaviour. He created two models - one with a vegetated façade and one without - and compared them in terms of key thermal comfort indicators: the MRT (mean radiant temperature), PET (physical equivalent temperature) and UTCI (universal thermal climate index). All these indicators improved in the green façade scenario.

The results clearly demonstrated the positive impact of vegetation on environmental quality at human level, i.e. approximately 1.5 meters above the ground. A lower level of heat stress was observed in the location with vegetation, confirming the sensibility of applying these systems specifically in densely populated areas.

Efficient, affordable, beautiful

Water consumption was found to be quite low - 1.15 l/m² of green facade per day. The price of one square metre of the facade without construction preparation was 13,500 CZK, which is comparable to high quality cladding materials. "We have been monitoring water consumption for a long time as one of the main economic indicators of green facades. The values confirm that it is comparable to the normal watering of houseplants in the home," adds David Bečkovský, one of the founders of the green walls research at the Faculty of Civil Engineering of the BUT. In addition to its air-conditioning function, the façade also increases biodiversity by attracting insects, capturing dust and emissions and visually enlivening the urban space

Green facades are one of the ways to use vegetation as part of the building fabric. More well-known and still more widespread are green roofs. When considering the possibility of applying a green roof and façade at the same time, it is necessary to think, for example, about rainwater management. Green roofs effectively reduce rainwater runoff from the roofs of buildings. However, if the investor also wants to use rainwater for watering the vegetated façade, the amount may not be sufficient. With regard to reducing the temperature of the building surface and the outdoor living space in cities, vegetated facades can be more beneficial than, for example, green roofs. "When designing a particular solution, it is ideal to have experts who have knowledge of both systems working on the project from the outset. In the design and implementation phase, the design of façades and roofs is a cross-disciplinary work. Particularly architecture, civil engineering and horticulture or landscape architecture. For proper design and implementation, an interdisciplinary dialogue is necessary to link the different disciplines and determine the design solution, suitable materials and plant species," explains Vystrčil one of the pitfalls of green walls. The research team is working on the topic of vegetated facades and green roofs and their interconnection, and believes that its contribution will become increasingly significant in the context of sustainable construction.

Research continues

Jan Vystrčil's dissertation is not the end of his research. He wants to further analyse the different types of vegetation facades, their long-term behaviour and the effect on the airflow in the ventilated gap behind the vegetation. He is also considering real case studies in urban environments and linking research to practice, for example by working with architects, developers or cities. In this context, work is also needed to quantify the long-term costs for different types of vegetated facades, their irrigation or maintenance and the suitability of their use in specific cases.

 

Green facades are not just an architectural experiment today, but are gradually becoming a functional tool for urban adaptation to climate change. Jan Vystrčil's dissertation provides evidence that greenery on facades has a measurable and positive impact on the environment in which we live.