Cluster Building Sector

Living and working, commercial activity, trades and services, culture and education, health and leisure – the buildings are used for, or closely connected with, a great variety of human activities. It has always been a core function of buildings to protect users and their properties from impacts of weather conditions. This also applies to the variety of functions which can be carried out in buildings. The existing building standards and norms ensure that buildings meet these requirements when confronted with a variety of climatic conditions prevailing at their location and that they are protected, as far as possible, from any predictable types of damage. Regional differences in terms of snow loads, wind pressures and heavy rain or in terms of summer climate regions are described. Such differences must be taken into account in the design of buildings – at both architectural and engineering levels.

In view of the considerable range of possible interpretations of existing standards, it is particularly the increase in frequency and greater intensity of extreme events which will present challenges to the building sector. Buildings and towns / cities must continue to provide users and residents with comfortable, healthy and safe conditions, whilst facilitating ongoing adaptation to potential weather extremes.

However, the adaptation to climate change is just one of the topical challenges currently facing the building sector. The increasing urbanisation in turn increases the demand for affordable new housing as well as commercial areas, especially in economically strong cities and their peripheries. At the same time, the challenge is to make the building sector greenhouse-gas-neutral by the middle of this century. To this aim, existing buildings are being successively refurbished and updated in the course of the next few decades, in order to reduce their energy requirements and to convert them to using renewable types of energy. Such long-term processes of transforming buildings and towns / cities comprise both the necessity and the opportunity to employ or develop solutions that serve both protection from and adaptation to climate change.

Recent years have very clearly demonstrated the impacts of climatic change on buildings, settlements and towns / cities. Stresses due to high temperatures have been experienced in the years 2018, 2019 and latterly 2022, especially by city inhabitants. In Berlin, Frankfurt am Main and Munich, hot days with daily maximum temperatures of 30 °C and more, as well as ‘tropical nights’ with temperatures not decreasing below 20 °C, have generally become more frequent than the nationwide mean (cf. Indicator BAU-I-1). This was particularly the case in the years mentioned above when the summer months of June, July and August were hotter than average. Moreover, hot days have occurred in towns and cities as early as May and as late as September. The specific temperature conditions in towns and cities are characterised by the ‘urban heat island effect’; the maximum intensity of this effect is closely linked with, among other things, the size and density of a town or city. In 2018 in Berlin, for instance, a maximum temperature difference between the inner city and the city’s periphery was observed which exceeded 11 °C. The effect magnifies the urban stresses on a town / city’s population, caused by high temperatures. It is so far not possible to ascertain to what extent the urban heat island effect is intensified by climate change (cf. Indicator BAU-I-2). The continuous urbanisation and densification of towns and cities goes hand in hand with increasing the area potentially affected by this phenomenon. Nationwide, rising temperatures increase the requirements for heat protection of buildings in summer. This is indicated by the so-called cooling degree days which have been significantly on the increase in Germany (cf. Indicator BAU-I-3).

In addition to heat, more frequent and more intensive heavy rain and flooding constitute highly relevant risks to settlements and buildings. In people’s collective memory the deluge-like rainfalls of the ‘Bernd’ low-pressure system in July 2021 will be remembered for its catastrophic effects, particularly in Rhineland-Palatinate and North Rhine-Westphalia, but also in other German Länder. There has been no other year since the beginning of nationwide radar detection of precipitation levels that indicated such a high proportion of settlement areas affected by rainfalls at the severe weather warning level (cf. Indicator BAU-I-4). The catastrophic events of July 2021 caused material damage to residential properties, household effects and business premises and led to insurance claims amounting to a total of 8.1 billion Euros, which is the hitherto highest claims expenditure in terms of property insurance for natural hazards. In addition to natural hazards, it is possible to take out insurance cover for material damage caused by storms and hailstones. Issues resulting from individual extreme weather events such as hailstorms in 2013, are a major case in point, with a view to the particularly high claims expenditure arising in that year (cf. Indicator BAU-I-5).

Concerning the DAS building sector action field, the 2021 Climate Impact and Risk Analysis (KWRA) envisages a high climate risk in terms of the incidence of damage to buildings from floodwater as early as the mid-century. The same applies to the risk of increasing urban climate stresses in conjunction with an expansion of areas affected by the urban heat-island effect. Likewise, the risk of adverse developments of the indoor climate was assessed as high. Any negative impacts from rising indoor temperatures can also affect the air quality and hygiene conditions, as high temperatures can favour the release of hazardous substances and mould infestation. As far as vegetation in settlements are concerned, the risk of adverse effects from rising temperatures, more drought periods and possibly more extreme and more frequent storms was assessed as medium up to mid-century, and as high up to the end of this century. Moreover there is a risk that the vegetation, owing to climatic changes, will become more vulnerable to pest infestation and disease thus losing its ecological function including the improvement of urban climates.

The DAS Monitoring Indicators can be used to thematise the challenges to the building sector from increasing heat stresses, especially in urban environments. Such thematisation is also possible with regard to the impacts of extreme events on the building stock. By comparison, the data situation is less favourable with regard to other consequences of climate change. Primarily this concerns the impacts of climate change on the interior climate of buildings. Whilst the existing indicator BAU-I-3 takes cooling degree days into account in terms of the prevailing external conditions, there is currently a lack of reliable data to illustrate changes in terms of climate-related comfort in rooms. Currently there are not sufficient data available to convey a picture based on in-situ measurements for the impacts of climate warming on the building stock. Another important theme that cannot currently be based on adequate data, concerns the impacts of climate change on the condition of urban vegetation. Satellite remote sensing provides opportunities for a nationwide monitoring of the vitality of urban vegetation. It is, for example possible, on the basis of Sentinel 2 data, to calculate the Disease Water Stress Index (DSWI) in order to observe the impacts of drought stress on urban verdure.¹³⁰

As far as response indicators are concerned, satellite remote sensing also offers starting points for new and continued developments. This technology allows the observation of the degree of urban verdure in greater detail than by the current indicator BAU-R-1 Recreational areas. In this respect it would seem appropriate to keep developing and assessing the urban verdure grid designed as part of the research project entitled ‘How green are Germany’s towns and cities?’ (Wie grün sind bundesdeutsche Städte?)¹³¹ The indicator BAU-R-2 also consults data collected by satellite remote sensing. In this context, it is imperative to keep an eye on further developments regarding the data situation, such as the quest for a higher resolution of satellite images and to be consistent in using them in order to optimise the indicators. In other respects the inadequate availability of data continues to act as a distinct barrier to the development of response indicators. For instance, it would be desirable to know, with a view to hazards to settlements from heavy rain and related flash floods or inundations, to what extent municipalities and districts are prepared to deal with such events in terms of maps indicating hazards from heavy rain. Neither are there any central data sources available for the adaptation of building stock. An apposite starting point might be the database outlining the refurbishment level of the building stock, which is currently being established. In addition to aspects of climate protection and energy efficiency, this data collection might also include precautionary measures applied to buildings, such as the use of materials relevant to adaptation or structural measures for protection from damage caused by flooding, storm or hailstones. Furthermore, regular information on the prevailing state of climate-related knowledge and regarding the attitudes of real-estate proprietors and the real-estate sector at large would seem desirable: For example, what is the current knowledge of climatic hazards to owned buildings and of precautionary measures, and to what extent is there a willingness to take such measures in line with the requirements of climate protection.

In the past, the political focus in the building sector prioritised the provision of sufficient and affordable housing. However, the energy transition currently experienced, made it necessary to include the objective of a successive development of climate-neutral building stock by means of energy-efficient building and refurbishing activities. In recent years, the adaptation to climate change has also become more and more essential with respect to a broad range of issues in town planning and the building sector in general. Dry and hot summers such as 2018 and 2019 as well as incidents of heavy rain in numerous locations have increased public awareness of the fact that buildings, villages and towns/cities have to become more resilient to cope with the impacts of climate change.

In urban areas it is essential to ensure close coordination of any developments in terms of building planning and design at urban, district and infrastructure levels. If town planning is well adapted to climate issues, it will provide ample green and blue spaces in its infrastructure thus offering the basic requirements for a healthy urban climate that facilitates lower stress even when hot or dry weather prevails. Owing to their intense urbanisation, cities face challenges in terms of maintaining or creating spaces which are conducive to urban climate balance and recreation (cf. Indicator BAU-R-1). Sufficient green structures and water structures also function as important components in the concept of a ‘sponge city’. The term signifies a type of rainwater management which entails, for instance, the creation of retention capacities in municipal parks and other suitable areas where rainwater is stored as close to the location as possible, thus making it available for reuse or for letting it seep into the aquifer or ultimately letting it drain into sewer systems. In case of heavy rain, areas available for flooding help to reduce pressure on the sewage system and to avoid the inundation of settlement areas. At the same time. water retained temporarily on those surfaces increases the effect of cooling by evaporation thus creating a reservoir which, in drought situations, can supplement the grey water supply to municipal green spaces.

The Federal Government supports climate-compatible town planning and development in a variety of ways: In their research projects – the Federal Institute for Research on Building, Urban Affairs and Spatial Development (BBSR) as well as the BMBF and the UBA – address issues in respect of research on climate adaptation and urban development. The direct exchange of communications with pilot municipalities is an elementary part of these projects, and their outcomes are regularly made available to towns, cities and municipalities. In recent years, special emphasis was placed on a more precise ascertainment of the volume and quality of urban verdure and its effect on the urban climate. In addition, municipal strategies for the safeguarding and development of urban verdure were assessed. The motivation underlying various activities does not need to arise from climate adaptation, because urban verdure also provides a number of positive effects for health, active mobility, social cohesion and biological diversity (cf. the strategy process for the White Paper ‘Weißbuch Stadtgrün’¹³²). In addition to technical and methodological assistance in terms of research projects, the Federal Government and Federal States also support climate-compatible urban development by means of promotional programmes: In the summer of 2022, the Federal Ministry for Housing, Urban Development and Building (BMWSB) started the Federal Programme entitled ‘Anpassung urbaner Räume an den Klimawandel’/ ‘Adaptation of urban spaces to climate change’ which promotes projects targeting the maintenance and development of publicly accessible green and open spaces. Within the framework of DAS the BMUV launched a programme entitled ‘Measures for Adaptation to Impacts of Climate Change’ primarily in order to support municipalities and municipal institutions in their efforts to adapt to climate change. Opportunities for advice, continued professional development and networking in the field of climate adaptation are offered to competent persons and stakeholders in municipalities as well as bodies responsible for social services. These opportunities are provided by the Centre for Climate Adaptation / Zentrum KlimaAnpassung (www.zentrum-klimaanpassung.de), founded in 2021 by the BMUV.

In the same way as adapted town planning, climate-compatible continued-development of the building stock is addressed by research and development. An important theme in this context is the greening of façades and roof spaces. Numerous town and municipalities promote the greening of buildings (cf. Indicator BAU-R-2). Opportunities for support are already available from Federal Government.¹³³ Besides, in research and development emphasis is placed on heat protection of buildings in summer, which – if planned correctly – can have synergetic effects on climate protection and adaptation (cf. Indicator BAU-R-3). In view of ongoing climate warming, heat protection in summer is gaining ever more importance for the quality of functionality and ambience in both public and private buildings. Another theme that requires to be addressed by research is the need to adapt structural norms or standards and regulations to changed climatic conditions so that climate adaptation is integrated from the outset in planning and construction of buildings.¹³⁴ In order to reinforce the role-model function of public buildings in terms of climate adaptation, the Assessment System for Sustainable Building (BNB) is currently being developed further, with the aim to facilitate the quality assessment of planning and building performances in respect of climate-compatible building outcomes, which can then be reflected in the certification system.

^{130 - Meinel G., Krüger T., Eichler L., Wurm, Michael, Tenikl, Julia, Frick A., Wagner K., Fina S. 2022: Wie grün sind deutsche Städte? Ergebnisse einer bundesweiten Erfassung. Bundesinstitut für Bau- Stadt- und Raumforschung (BBSR) im Bundesamt für Bauwesen und Raumordnung (BBR). Bonn, 62 pp. https://www.bbsr.bund.de/BBSR/DE/veroeffentlichungen/sonderveroeffentlichungen/2022/wie-gruen-deutsche-staedte.html.}

^{131 - Meinel et al. 2022, cf. endnote no. 130.}

^{132 - BMUB – Bundesministerium für Umwelt, Naturschutz, Bau und Reaktorsicherheit (Hg.) 2017: Weißbuch Stadtgrün – Grün in der Stadt – Für eine lebenswerte Zukunft. Berlin, 51 pp. https://www.bbsr.bund.de/BBSR/DE/veroeffentlichungen/ministerien/bmub/verschiedene-themen/2017/weissbuch-stadtgruen.html.}

^{133 - Mann G., Fischer B., Fischer S., Gohlke R., Mollenhauer F., Wolff F., Köhler M., Pfoser N. 2022: Förderrichtlinie Dach- und Fassadenbegrünung – Machbarkeitsstudie. Bundesinstitut für Bau-, Stadt- und Raumforschung am Bundesamt für Bauordnung und Raumwesen (Hg.). 105 pp. https://www.bbsr.bund.de/BBSR/DE/forschung/programme/weitere/gruen-in-der-stadt/machbarkeitsstudie-gebaeudegruen/endbericht.pdf.}

^{134 - Kind C., Golz S., Sieker H. 2022: Klimaanpassung und Normungsverfahren. Analyse bestehender bautechnischer Normen und Regelwerke für einen Anpassungsbedarf an die Folgen des Klimawandels. 85 pp. https://www.bbsr.bund.de/BBSR/DE/forschung/programme/zb/Auftragsforschung/5EnergieKlimaBauen/2019/klimaanpassung/endbericht.pdf.}