The Green Vienna – greening of the Gemeindebau in Vienna to reduce urban heat islands

Vienna is getting hotter and hotter. High building densities and increasing degrees of sealing as well as rising temperatures due to climate change are causing the city to heat up significantly more than the surrounding area. This urban heat island effect (UHI effect) can be counteracted by raising the proportion of green space. However, because green spaces must often give way to residential buildings and the pressure for use of public space is increasing, the greening of roofs and facades offers an efficient addition as it does not take up any additional space but, among other benefits, has been shown to have a positive impact on the microclimate.

A high potential for building greening is offered by the approximately 1,800 municipal buildings owned by the City of Vienna. The Gemeindebau represents a special feature in social housing and is internationally regarded as a best practice, not least because of the large number of buildings that are spread throughout the city and house about a quarter of the Viennese population. They originated during the time of “Red Vienna” and until today all buildings are entirely owned by the City of Vienna. So, what if the Gemeindebau could contribute to mitigating urban heat by gradually greening these buildings? What would happen if “Red Vienna” became “Green Vienna”?

The questions of how a greening offensive can succeed in Vienna and why the existing residential buildings owned by the City of Vienna are the ideal starting point for this are explored based on information on climate change impacts in Vienna, the UHI effect, building-related greening as well as the history of municipal buildings. A spatial analysis of the location of municipal buildings within urban heat islands forms the basis for the development of a criteria grid, which provides a foundation for decision-making to prioritise the municipal building stock regarding greening measures. A model calculation shows expected costs and scale of benefits from measures combating heat stress. The analysis of heat locations is based on the so-called Urban Heat Vulnerability Index (UHVI) that considers residents who are particularly affected by heat due to their age (0-14 and 60+) and thus indicates the heat tolerance in a specific area.

A large part of our city of tomorrow has already been built. Therefore, it is essential to use the potential of the existing building stock and to make housing an integral part of climate change adaptation. The contribution that the greening of municipal buildings can make to reducing urban heat islands depends on the quantity and quality of the measures applied. The cooling performance varies greatly depending on the system in question. The more of the criteria are fulfilled, the higher the cooling capacity of the measure and thus the contribution to cooling the city. The results show that greening municipal buildings is both economically feasible and can be a significant component on the path to climate neutrality, as the potential in terms of surfaces is almost inexhaustible and the costs of those measures are low relative to the cost of inaction. In addition to ownership of structures in the Gemeindebau facilitating implementation and the large number of buildings, these measures can become a significant lever for the entire city and beyond due to the role model effect, while preventing social inequality that often comes with climate change adaptation measures.