Grey emissions can be measured and limited more effectively: researchers in the KEA-Bauwerk project are developing basic principles and tools to reduce energy consumption and CO2 emissions in the life cycle of buildings. They are identifying practical data and benchmarks, for example.

In Germany, there are almost 20 million residential buildings and nearly two million non-residential buildings, which fall under the scope of the German Buildings Energy Act (Gebäudeenergiegesetz (GEG)). All these buildings, from multifamily homes to office complexes, consume energy for heating, cooling, and water heating. Annually, the operation of buildings accounts for more than 30 % of energy consumption in Germany (approx. 3,084 petajoules and thus around 184 million tonnes of CO₂ in 2019). In order to achieve climate protection goals, buildings in operation must be supplied with energy in a climate-smarter and more efficient way.

However, is a building supplied entirely from renewable sources automatically climate-neutral in its life cycle? No, because grey energy and grey emissions (i.e. the amount of energy required and emissions created to produce the individual components) must also be taken into account. In addition, energy consumption and emissions that occur throughout the building’s life cycle as a result of repairs and modernizations, and finally the demolition and disposal of the components, must also be accounted for.

How can grey energy and grey emissions be measured and limited?

With regard to climate protection goals, grey emissions should also be reduced. Researchers from the Karlsruhe Institute of Technology (KIT) investigate how this can be achieved in the future in the KEA-Bauwerk project, which aims to create basic principles and tools to minimize energy consumption and greenhouse gas emissions in the life cycle of buildings and to contribute to IEA EBC Annex 72. The findings of the research project will not only be incorporated into national directives but also contribute to decreasing energy consumption and greenhouse gas emissions in the life cycle of buildings at international level as part of IEA EBC Annex 72.

“The starting point for our project are discussions at international, European, and national level,” explains project leader Prof. Thomas Lützkendorf. “The question is whether, when, and how the consumption of non-renewable primary energy as well as greenhouse gas emissions in the life cycle of buildings can be limited, and how this can ultimately lead to the implementation of binding requirements in funding programmes and laws.”

The KEA-Bauwerk project will establish and develop the methodological foundation to answer these questions. Such an applied life cycle assessment (LCA), which involves using the ecological balance of a building, is multifaceted since many aspects are intertwined. For example, using insulation material, which requires less energy to produce but which insulates less effectively, reduces the amount of grey energy consumed and the grey emissions decrease. In the long term, however, the building consumes more energy for heating, which means that greenhouse gas emissions increase.

The researchers are therefore investigating, for example, whether there is an optimum between the energy required for production and maintenance on the one hand and the energy required during the utilization phase on the other hand. In addition, they are exploring how the utilization phase can be precisely differentiated and how the generation of renewable energy in or on the building can be included in the assessment process. They are also studying the particular features associated with biomass and the carbon content of building products as well as the ways in which compensatory measures can be formulated and recognized.

The more efficient buildings become, the more the focus shifts to grey emissions

What is considered climate-neutral? A matter of definition

These considerations started with the question of what is actually considered climate-neutral since the definition varies depending on the assessment model and country. The researchers analysed 35 different approaches according to which buildings can be certified in different countries. The KEA-Bauwerk team found the most ambitious approaches in Canada, France, Germany, Norway, Sweden, the UK, and the USA. All these certificates focused on achieving greenhouse gas neutrality throughout the full life cycle.

What is building information modeling (BIM)?

Building information modeling (BIM) is a method of digital planning that involves creating a digital twin of a building. Using this digital model, planning, construction, and operation of the building can be optimized and it is possible to respond quickly to any changing requirements. The issue of LCAs can also be integrated into the BIM process.

However, the various methods differed with regard to the questions of how the use of electricity is taken into account in terms of corresponding emission factors, how the time aspect is included, and how emissions can be compensated. Another study shows the impact of these differences. Here, the researchers investigated the CO₂ emissions of a reference building using 17 different international approaches and databases related to life cycle assessment.

According to the study, the biggest differences between the various methods include the data on the building products LCA that were used for the analyses, the system boundaries of the building and life cycle model, and the period under consideration. However, although the calculated greenhouse gas emissions for the reference building differ, the individual results are relevant for comparisons in the respective national context. The researchers conclude that it is important that benchmarks correspond to the particular LCA approach and the data basis in the respective country. They also found evidence that the production and maintenance of building constructions make a significant contribution to the environmental impact of buildings and should therefore be included in life cycle assessments.

Strengthening knowledge of fundamentals and tools in architecture and construction planning

The researchers concluded from the results that not only relevant data and tools support an increased use of LCAs. In addition, it is important to establish standards and legal requirements to drive client demand. “We expect that binding provisions to limit greenhouse gas emissions in the life cycle of buildings will be introduced in Germany in the medium term,” says Lützkendorf. “Until then, architecture and construction planning should be prepared for this task and the industry should be provided with the necessary knowledge and tools for life cycle assessments. The demand must then come from the investors and building owners – initiated and increased by factors such as advantages in financing and valuation or due to legal requirements.”

Results are incorporated into national and international standards

The results of the KEA-Bauwerk project are being incorporated into the discussion on the development of European standards, which are also being adopted in the German set of standards, including DIN EN 15643 and the future EN 15978-1. The results directly contributed to the balancing rules for the German quality seal for sustainable building (QNG) and are currently playing a role in the discussions on a future GEG. The international cooperation within the framework of the IEA project collaboration has also led to the fact that information on the creation and development of databases is now being used in India.

After the conclusion of the IEA project at the end of 2022, project reports with detailed information, practical examples, and recommendations for action will be published. (Editorial note: After their publication, the reports will be made available at (ks)

  • the standardized operational energy expenditure during the utilization phase of buildings, the non-standardized operational energy expenditure, and the user- and use-related expenditure
  • the energy produced/generated in/on the building (building-integrated) or on the property (near the building), including exports and the consideration of corresponding effects regarding the operational and building-related greenhouse gas emissions
  • biomass in ecological balancing using the 0/0 or -1/+1 approach
  • benchmarks and target values including their description
  • additional requirements and guide values for requirements
  • effects outside the system boundaries in the form of recycling potential and emissions potentially avoided in third parties
  • compensatory measures to achieve a net-zero emission balance
  • additional indicators to identify undesirable side effects and avoid a shift in loads
Zuletzt aktualisiert am: 24.08.2022

At a glance 

Funding reference no: 03ET1550A

Project duration: 1 January 2018 30 November 2022 Today

Topics: Energy-optimized buildings

Funding: € 338,125 


Karlsruhe Institute of Technology (KIT)
Sustainable Management of Housing and Real Estate

Tel: +49 721 608 4 8336

Digital tools, concepts, and methods

Information and communications technology plays an important role in buildings and districts, as innovative building technology and the electric, thermal, and digital networking of buildings, districts, and energy systems can help to significantly optimize their energy performance.


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