Why Europe Needs One Language
for Building Performance
From A to G, those colour-coded labels pinned to every house, apartment, or public building show how efficiently it uses energy. These Energy Performance Certificates (EPCs) do more than tick a legal box: they help determine who receives support to renovate and who does not. Yet across the EU, the way we calculate building performance still differs widely between Member States.
Those differences matter because Energy Performance (EP) data underpin decisions on where renovation programmes will deliver the greatest impact. When performance is measured one way in Lisbon and another in Ljubljana, results cannot be compared fairly and public money risks flowing to whoever has the most generous methodology rather than the greatest need.
The EU’s push for a single, converged approach to building performance is a question of fairness and level playing field ambition. Reliable, comparable data allow Member States to target renovation support more accurately, plan their energy transitions more credibly, and prove that European funds are spent where they make the biggest difference. This is what the European funded project openBEP4EU is striving to achieve.
How does reliable EPC data influence renovation planning for municipalities and social-housing providers?
The work with EPCs can serve several purposes. Beyond the legal requirement, an EPC gives insight into a building’s energy performance and potential — though only at a static level. Many building owners use the EPC as a lever when applying for investment funding from foundations or banks.
The obvious cases are the energy-saving measures listed in the EPC that have short payback times, as these are ‘easier’ to obtain financing for. But there can be more good cases if EPC recommendations are combined with long-term operation and maintenance plans that look many years ahead in the building’s lifetime.
Here in Brøndby, we are in the process of renewing the EPCs for the municipality’s own buildings in order to apply for Green Energy Loans to help finance upcoming renovations. This also ties into the Energy Efficiency Directive’s requirement to lift public buildings towards NZEB [nearly zero-energy buildings].
From Everyday Life to EU Policy
For citizens, EPCs influence more than abstract policy. They affect the price of homes, eligibility for renovation grants, and whether tenants in social housing see their buildings upgraded or left behind. A certificate with a higher grade can make the difference between qualifying for a low-interest loan or facing rising energy bills.
Municipalities rely on aggregated EPC data to decide which neighbourhoods to prioritise for retrofits. Private banks use them to design green-finance products. And if the underlying data aren’t consistent, entire investment programmes rest on uncertain ground.
How does open and comparable data improve market confidence or digital tool development?
From a software developer’s perspective, open and comparable EPC data are what allow digital tools to scale across borders instead of being rebuilt for every country. When the calculation engine is based on the EPB standards and exposed through open interfaces, we can validate algorithms once, reuse them many times, and focus development effort on user‑friendly services rather than on decoding national quirks.
For markets, that transparency builds trust: investors, banks, and public authorities can see how results are generated, compare portfolios on equal terms, and link EPC data directly to renovation and financing products.
In short, open data and open methods reduce technical risk and make it much easier to bring innovative tools to the entire EU building stock.
The Standards Behind the Numbers
To address that, the recast Energy Performance of Buildings Directive (EU) 2024/1275 requires all Member States to describe their EPC calculation methodologies in line with a shared technical foundation: the CEN/ISO 52000 family of Energy Performance of Buildings (EPB) standards. Adopting these standards directly as the calculation method is the simplest and recommended option. These standards describe, in mathematical form, how energy use, heat transfer, lighting, and ventilation are assessed. The EPB standards are consensus‑based CEN/ISO documents that provide harmonised, transparent, and software-ready procedures for assessing building energy performance, supporting both regulation and design.
openBEP4EU is translating this framework into an open-source EP calculation engine so it can be applied consistently across Europe. Rather than replacing national systems, the goal is to make sure that the logic behind every calculation is traceable and comparable. National EPC systems remain in place, while openBEP4EU contributes an EPB-based common calculation layer, including a Smart Readiness Indicator (SRI) engine and shared data libraries, that Member States can integrate into their existing platforms or use as a reference for assessing alignment with the CEN/ISO set of EPB standards. The same open toolbox also underpins a European Sustainable Design Data Hub, making it easier for countries to share and reuse building‑ performance data in line with the Energy Performance of Buildings Directive (EPBD) recast.
• The EPC (Energy Performance Certificate) is the rating and label issued to the building following an EP (Energy Performance) assessment.
• The EPB (Energy Performance of Buildings) standards are the harmonised calculation methods that define how the rating is obtained.
The Buildings Providing Data
Five sets of buildings across Europe are providing data to test the approach in openBEP4EU. Together, they supply evidence for one open calculation core. Each building type helps verify that the same logic holds whether applied to a museum, a social-housing complex, or a university campus.
• In Aspra Spitia, Greece, identical post-war housing blocks reveal how small differences in data handling affect results.
• In Denmark, urban and rural buildings provide contrasting climate conditions for the same calculation engine.
• Spain contributes mixed apartment blocks in Murcia; Cyprus adds warm-climate housing; and Switzerland contributes methodology alignment for colder regions.
Current Tools and National Systems
With the current tools and national systems in place, Joint Research Centre reported persistent gaps in data quality and training across Member States. Consumer organisations such as ANEC say certificates remain difficult for households to interpret, and many experts argue that transparency must extend beyond software to the people carrying out the assessments.
openBEP4EU’s open-source model aims to close these gaps by making every step of the calculation visible. Anyone, from a researcher to a municipal planner, can see how results are generated, improving both accountability and reusability. Read more about the tools in use now >
What Member States Gain
For Member States, the benefits go beyond comparability. Harmonised EPC data help make renovation planning and funding more evidence-based. While EPCs are not the only factor, comparable results give Member States and EU bodies clearer insight into where improvements would deliver the best value. When data show that one country’s building stock already performs well, as in Denmark or Finland, the Commission can justifiably prioritise more direct renovation aid to regions where improvements deliver greater impact. High-performing countries, in turn, can focus on innovation, digitalisation, and export of expertise rather than basic efficiency upgrades. This does not punish success; it clarifies priorities. Transparent, harmonised data make spending defensible and attract private investment. Banks and energy-service companies trust information built on the same calculation logic used across Europe. For policymakers, it provides a solid base for long-term planning instead of repeated pilot schemes and ad-hoc corrections.
What does using the CEN/ISO set of EPB standards actually change for assessors or public authorities?
Using the CEN/ISO set of EPB standard means that assessors and public authorities are no longer working with a patchwork of incompatible rules, but with one common technical language for assessing, certifying, and managing building performance.
For assessors, it clarifies which data to collect and how to calculate indicators, so software tools and results are consistent, traceable, and easier to explain to building owners.
For public authorities, it offers a transparent and consensus-based framework where national choices are clearly documented yet aligned with the same European core. That is what turns EPCs from a simple administrative form into a robust instrument to plan renovations fairly, compare buildings on equal terms, and channel finance where it has the greatest impact.
The Fairness Thread
Reliable data help governments justify renovation budgets and identify where support is most needed, not just those easiest to measure or those in countries with the most favourable software. They help governments defend renovation budgets, allow citizens to understand the value of upgrades, and give Europe a coherent way to track progress toward climate-neutral buildings.
In that sense, one language for building performance is not just a bureaucratic exercise. It’s a technical foundation to increase trust between Member States, between institutions and citizens, and between the numbers on a certificate and the energy use behind them.
Hopefully, shared standards will provide every Member State a more fair starting point, turning building data into decisions that improve homes, communities, and climate targets alike.