The waste heat generated from the use of air conditioning systems in cities significantly contributes to the urban heat island effect (UHI) during the summer months. Thus, one of the key measures to mitigate this effect is to limit the use of active cooling systems. In the city of Vienna, air conditioning units are common in nonresidential buildings, but have so far been much less installed in residential buildings. This is mainly due to the fact that the Viennese summertime climate is still considered to be relatively comfortable and planning guidelines related to energy efficiency are already strict, resulting in high-quality buildings in regard to thermal performance. However, during the last decade, an increase in summertime temperatures and so called “tropical nights” has been recorded in Vienna and subsequently the postconstruction installation of air conditioning systems in residential buildings has significantly increased. In a study undertaken for the City of Vienna, a series of passive design measures have been simulated with current and future climate scenarios in order to determine the most effective combination of architecturally driven actions to avoid the use of air conditioning systems in residential buildings whilst maintaining comfortable indoor temperatures.

In urban areas, summer temperatures are continuously increasing, and cities are aiming at implementing measures to mitigate the urban heat island (UHI) effect. Reducing sealed surfaces and adding plants have been shown to be beneficial for urban microclimates. Green roofs are thus a viable alternative to standard roofs made out of materials that completely seal the top layer. However, roofs are, at the same time, also ideal for the integration of photovoltaics (PVs), as they are mostly unshaded. With both applications competing for the same surface area, solutions must be found that symbiotically combine the benefits of vegetation and renewable energy. Using an interdisciplinary study, various designs were developed for prototypical applications to integrate PV systems into rooftop gardens, with a specific focus on retrofitting flat roofs. The prototypes were analyzed and tested based on structural design aspects, suitable plant choices, and energy output. The results showed that the concurrent integration of PVs and green roofs into the same surface area can be achieved with lightweight construction, which is particularly suitable for existing buildings. The system can contribute to much-needed urban renewable energy generation, the mitigation of the UHI effect, and the provision of recreational spaces.

Building refurbishment plays a key role in the de-carbonization of the European building stock. Whilst the renewal of the thermal envelope increases energy efficiency during the operational phase, the type of material is highly relevant for the overall environmental impact of the refurbishment. Expanded polystyrene (EPS) is most widely used for external thermal insulation systems but is also a material based on fossil resources. Thus, alternatives made from renewable raw materials must be more widely used in order to reach the climate goals. However, comparable data on long-term material effects over the life cycle are needed for developers and planners to make informed decisions. In a Viennese case study for the largest social housing property manager in Europe, two different façade systems have been analyzed to assess the overall environmental impact of the materials. In a comprehensive life cycle assessment, a Multi-Active Façade system based on recycled paper has been compared with a conventional external thermal insulation composite system (ETICS) using EPS. It shows that whilst the evaluation during the operational phase alone results in a similar ecological footprint of the ETICS, the analysis over the whole life cycle provides a clear positive indication for the novel Multi-Active Façade.

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