Buildings are pivotal in achieving climate neutrality, as their operation alone accounts for about one-third of the energy-related greenhouse gas emissions in Germany. Many crucial decisions are made in the early planning phases of modernizations or new constructions. However, there is currently no adequate tool available for estimating lifecycle energy and emissions at this stage, which provides robust lifecycle assessments with minimal input and can also be used by interested laypersons. The goal of the LezBAU project, funded by the Federal Ministry for Economic Affairs and Climate Action, is to develop a tool that can be used for free with relatively few inputs and low entry barriers. To achieve this, scientists and architects are working closely together in the tool’s development. Additionally, early and continuous exchange with a project advisory board, stakeholders, and participants helps to make the future tool practical and well-known.

Both the European Union and Germany have set climate neutrality as a legally binding goal. To achieve this goal decarbonizing the building sector is essential, as building operations alone are responsible for around 35 percent of final energy consumption and 30 percent of CO2 emissions (BMWK, 2023). Besides these operational energy consumptions, which have been the focus so far, other building-related consumptions and emissions must also be considered to achieve climate neutrality in the building sector: the emissions from the materials used for construction, transport, erection, maintenance, and demolition of buildings. However, planners and especially building owners currently lack adapted tools for decision-making towards climate-friendly building materials in the early phases of building planning.

The environmental impacts of buildings over their entire lifecycle can be quantified using Life Cycle Assessments (LCA) based on methodologies established in existing standards. If such LCA data is available in the early phases of the planning process for building modernizations or new constructions, it can enable decisions that reduce the environmental impacts of buildings (Bogenstätter, 2000; Braganca et al., 2014). However, Lützkendorf et al. (2020) show that only about 16% of architects in Germany currently use the LCA approach in their projects, despite a clear majority being familiar with the concept. Barriers to the use of LCA include a lack of in-house expertise (for 56% of respondents), time requirements (for 42%), data shortages (for 34%), and cost (for 22%).

Against this backdrop, the LezBAU project was initiated under the leadership of the Institute for Housing and Environment (IWU) in Darmstadt, with funding from the German Federal Ministry for Economic Affairs and Climate Action (BMWK). Research partners include the German Environmental Aid (DUH) and the Frankfurt University of Applied Sciences (FRAUAS). The research participants are the Arge B.A.U.-LezBAU GbR, consisting of members of the Bundes Architektur & Umwelt e.V. (B.A.U.). The goal is to develop an easy-to-use and, above all, freely available online tool that allows lifecycle impacts to be estimated in the early planning phases. The tool is primarily aimed at smaller projects in modernization and new construction, which make up a significant portion of the construction volume in Germany and for which the use of a commercial LCA program would lead to disproportionate cost increases.

The LezBAU tool is intended to complement the existing set of lifecycle calculation tools in the building sector with a critical component. Detailed calculations can already be performed today with commercial software such as LEGEP or Generis, which lead to precise results and may be approved for certification. However, a disadvantage is that only limited information is available in the early planning phases, making detailed LCA difficult. Therefore, assumptions must be made to supplement the missing data with plausible values (Hollberg, 2016; Röck, 2018). Another possibility is to combine LCA with Building Information Modelling (BIM) using scripts or commercial interfaces (Tally, One Click LCA, CAALA) (Röck, 2018; Hollberg, 2018). In this case, data on building geometry (and possibly building materials) is taken from the BIM model. This approach may be more suitable for early planning phases if BIM models are already available, which is rarely the case (BIM is standard for only 18% of the surveyed architects, see Lützkendorf & Balouktsi, 2020). Additionally, simple checklists, such as the SNAP method, can provide rough estimates for the lifecycle analysis of buildings, although they can only offer more general guidance. Available software for the usage phase of buildings usually relies on secondary software, potentially resulting in double data entry efforts. The capture of so-called embodied energy or embodied emissions is usually not combined with energy use and the corresponding greenhouse gases in the usage phase.

There is a need for a tool that facilitates practical and integrated lifecycle assessment: the LezBAU Tool. Besides the tool itself, extensive catalogues of example buildings (existing, new constructions, residential, and non-residential buildings), components, and systems will be developed, which were previously unavailable. A scaling method will also be created to adapt the example buildings provided by the tool to specific applications. By developing simplified catalogues of components and systems and integrating them into a simplified LezBAU Tool, important foundations for creating scenarios for building stocks will be established. Existing classifications for buildings in the lifecycle will be tested against climate protection goals using the LezBAU Tool. To apply the assessment to energy-efficient modernization, existing calculation methods for the assessment of new buildings will be further developed. This includes researching existing LCA benchmarks and developing general benchmarks for buildings in Germany (residential and non-residential, new and renovated) based on them. Additionally, tool-specific benchmarks (LezBAU) will be developed by defining and calculating best-practice and business-as-usual variants.

As shown in Figure 1 users begin by selecting a building from a catalogue that most closely matches their project. The example buildings provided are typically completed projects where feasibility in terms of fire protection, sound insulation, structural stability, financing, etc., has already been demonstrated in practice. In addition to the selected type, rough dimensions of the user’s construction project can be provided for scaling. Further selection of materials and building technology is possible but not necessary for the subsequent calculation steps, as predefined calculation values are already stored in the tool with the type selection. By entering the data, the tool then calculates a lifecycle assessment of the planned building, which can be displayed in a PDF document. It is also planned to generate intermediate results to show optimization possibilities through the use of other materials or constructions. Users can save intermediate states and reuse them in the LezBAU Tool for further editing at a later time. Thus, no (project) data remains on the LezBAU project’s servers after processing. The goal of the tool is to provide information with minimal input effort that can significantly reduce the CO2 emissions of the object—whether it is a modernization or a new construction of a residential or non-residential building. Additionally, the tool may also form the basis for future certification after its completion.

Figure 1: Methodology of the LezBAU Tool

The initial concept for the LezBAU Tool arose from practical experience, represented in the consortium by the working group B. A. U. GbR. Previously, lifecycle aspects were inadequately or not at all considered in the early planning phases from the perspective of architects. This led to a project and development design where practical experience is not only considered but directly integrated into the tool development work in the spirit of co-production. Additionally, through the project partner DUH and its extensive network, there is a close connection to relevant policy processes in the building sector, which should help the LezBAU Tool have an impact in the broader governance context. Contributions from FRA-UAS bring indispensable expertise in building technology and provide an opportunity to use the LezBAU Tool in the education and training of the next generation of specialists in the building sector. The IWU contributes its scientific expertise in the building sector, building modelling, lifecycle assessment, project management, and tool development, and coordinates the work processes significantly.

After initially developing the conceptual foundations within the consortium, the first project advisory board meeting took place in Berlin in September 2023. The initial project concept was presented to experts from various areas of the building sector and discussed together. This exchange showed that optimization possibilities should be more strongly integrated into the tool. Additionally, it was discussed to what extent the databases for building components and technology should be made available as Open Data. This is necessary to reach the majority of small projects, which are relevant for achieving climate goals, with low barriers. Building on these discussions, the first stakeholder workshop took place as planned in October 2023 in an online format, with 59 participants from politics, research, industry, associations, and practice. Here, too, the great potential benefit of the LezBAU Tool was evident. Once again, the importance of optimization possibilities for designs within the tool was emphasized.

In the building sector, as in the transport sector, the legally binding targets of the Climate Protection Act for Germany have not been met. However, these targets only address the combustion of fuels in buildings (electricity consumed in buildings is attributed to the energy sector, not the building sector), while embodied energy and associated emissions from the production of building materials, as well as from the construction, maintenance, and demolition at the end of a building’s life, have so far received little attention in socio-political awareness and control processes. At the same time, it is becoming clear at the European and international levels that Life Cycle Assessments (LCA) are increasingly coming into focus in the building sector (see, for example, contributions in Azari & Moncaster, 2023). With decreasing operational energy, the percentage share of embodied energy or embodied emissions of a building over its lifetime correspondingly increases (Bischof and Duffy, 2022). Against this backdrop, solutions are needed that allow planners and architects to estimate lifecycle emissions early in the planning process—when essential and often irreversible decisions about modernization or new construction are made. Additionally, building owners should be enabled to make their own estimates and use these as a basis for discussions with planners.

The LezBAU Tool is designed to provide such an opportunity. It contributes to climate protection in the building sector and thus to the common good by being offered free of charge and internet-based. This aims to reach and inspire the multitude of smaller architecture and planning offices that would otherwise not be able to acquire and/or use the corresponding software. Also, with a view to the broader governance landscape, the LezBAU Tool can have an impact—whether by increasing the demand for ecologically sensible building materials or by further developing governance approaches to reduce lifecycle energy and emissions in the building sector. Based on the current state of work, we can expect the new tool to be accessible to the interested public in the course of 2026.