Green Facades
Measuring their Environmental Benefit
Green roofs and planted facades have become a familiar feature in urban planning and construction – and their benefits are considerable, not least in relation to climate change and the measures needed to address it. In densely built environments, sealed surfaces store heat and turn cities into so-called urban heat islands, exposing residents to higher temperatures. Green facades can help counter this effect. Through transpiration, plants act as a kind of green skin on the building – they “sweat,” releasing moisture and cooling the surface. As a result, the building envelope heats up less, indoor temperatures rise more slowly, and less heat is radiated back into the surrounding urban environment.
A current example at RWTH is the new building for the Institute of Transport Science (VIA), which features extensive use of wood and integrated greenery. According to the Building and Real Estate Management Agency of North Rhine-Westphalia, “a three-sided green facade makes the building’s sustainability concept visible from the outside. The planted panels are pre-grown in greenhouses, trained for vertical growth, and then installed on the facade” (see also the press release Nachhaltiger Holz-Hybridbau für die RWTH). The benefits of the green facade are clear: In addition to helping regulate temperature, it improves air quality and enhances the quality of the surrounding outdoor space.
But how significant is the ecological impact of a green facade? A research project at the Chair of Building Technology led by Professor Daniele Santucci is examining this question. Initial work began in the summer semester of 2024, when researchers from the chairs of Landscape Architecture and Building Technology conducted prototype measurements using a student-developed system known as the “BauGrünKit” (which was featured in the University’s second Sustainability Report). Building on this, the facade of the VIA’s new timber-hybrid building is now being examined.
Innovation Through Sensor Fusion
The project measures particulate matter, CO₂ concentrations, air and radiant temperatures, and humidity to assess the thermal performance of green façades. As the researchers explain, “together with measurements of air temperature, humidity, and air quality, the sensors generate a robust dataset for analyzing thermal comfort.”
The team uses a custom-built measurement system developed by Harald Lesan at the Chair of Building Technology. “At its core, we use a standard experimental setup with small IoT devices—IoT meaning Internet of Things,” he explains. “We also deploy thermal imaging cameras and distance sensors to build a three-dimensional picture of how the facade reflects radiation. Combining these different data streams, known as sensor fusion, is what makes our approach innovative.”
The project also captures the subjective perceptions of passersby, which are analyzed qualitatively and compared with the measured data. The aim is to use this approach to predict how ecological factors influence the well-being of building users. The researchers hope to apply the measurement method to other facades, enabling predictions for comparable systems — with potential economic benefits as a further outcome.
The technical setup relies on a local network in which IoT devices continuously collect environmental data, including particulate matter, CO₂ concentration, air temperature, and humidity. A mobile measurement station supplements this with thermal imaging, capturing radiation patterns in three-dimensional space. Together, these data help build a more precise understanding of how green facades influence the urban microclimate.
The project “Thermal Performance of Green Facades” is funded by RWTH’s Sustainability Fund, which supports initiatives in research, teaching, and operations that contribute to a more sustainable University.