1. Stage 1: before design
Four checks precede everything else, and the second is particularly important at present. They concern establishing the requirement.
| Check | Why |
|---|---|
| Fix when the application will be submitted | determines the applicable version |
| Check the date of entry into force in the legislation | entry into force has been amended |
| Determine whether this is a new building, substantial reconstruction or neither | two different requirement levels |
| Check whether an exemption or relief applies | they are not the same thing |
The second check matters especially in 2025 and 2026, since entry into force was changed from 1 March to 1 June 2025. Two regimes ran in parallel.
2. Stage 2: early design
Four decisions that cannot be compensated for later. They are made in the first design phase.
The building's shape, orientation and volume determine the basis of the energy demand. Roof orientation, pitch and shading may determine which requirement applies at all. The basic solution of the external envelope determines the size of the demand.
Fourth, commission the calculation early enough for it to influence the solution rather than merely evidence compliance. This distinguishes a useful calculation from a formal one and is the decision with the greatest effect for the client.
3. Stage 3: calculation and certificate
Four checks before commissioning and after delivery, with one more where uses are mixed. They concern the content of the certificate.
| Check | When |
|---|---|
| The specialist's competence in the professional register | before signing the contract |
| The limit value from the annex to the regulation in force | not from an earlier project |
| The regulation's concept of area, not the register's | the basis of the calculation |
| The certificate is in the building register | a document outside the register is not an energy certificate |
For a building with several uses a fifth check is added: whether the weighted average has been calculated for the result and for the limit value alike. Otherwise the result is wrong.
4. Stage 4: occupancy and beyond
Three things follow, and the third holds even where it is widely ignored. They concern the register and retention.
The ETA's two-year validity runs from the issue of the occupancy permit, and after two years a certificate based on actual data is prepared, valid for ten years. On a sale or a letting the energy class must be stated in the advertisement, as covered by the article on what to watch.
5. What to take from the regulation, not memory
Four things this guide deliberately does not state, because a wrong value is harmful here. They must be taken from the regulation in force.
The limit values for the energy performance value, which changed on 1 June 2025. The definition of substantial reconstruction. The definitions of room-temperature and heated area. The precise wording of the exemptions. All four are in the text of the regulation in force, and none can safely be memorised.
6. Five critical moments
At these moments an error becomes expensive, and the fourth is the likeliest with an experienced designer. They are the decision points of the project.
| Moment | Why critical |
|---|---|
| Signing the design contract without determining the applicable requirement | the whole project rests on a wrong basis |
| Deciding shape and orientation without assessing roof area | may change which requirement applies |
| Commissioning the calculation too late | it evidences but no longer influences the solution |
| Reusing an earlier project's limit value | the values changed |
| Commissioning a specialist without checking competence | the certificate is unusable in the procedure |
7. What applies to an existing building
Three steps, and the third matters to a seller and is rarely weighed. They concern a sale and a letting.
Check in the building register whether a valid certificate exists and when it was issued. Do not compare classes from certificates issued at different times directly, since the scale and methodology have changed. Weigh before commissioning a new certificate whether replacing a valid one is beneficial, because the class may change without the building having changed.
8. One sentence that sums up the guide
Three statements that are really the same statement seen three ways. They all reduce to the regulation in force.
Energy performance is not one technical requirement among others but a condition of the permit procedure. Without a calculation meeting the requirements, neither new construction nor substantial reconstruction moves forward. And the result of that calculation is settled by choices made before any device has been chosen.
Summary and four practical rules
The process divides into four stages: determining the applicable requirement before design, the early decisions on shape, orientation and roof, the calculation together with competence and register checks, and occupancy, from which the ETA's two-year validity runs. The limit values, the definition of substantial reconstruction, the area concepts and the wording of the exemptions must be taken from the regulation in force rather than from memory. Of the five critical moments the likeliest is reusing an earlier project's limit value, precisely because of experience.
Four rules: determine the applicable requirement before the design contract. Assess the roof and orientation in the first phase. Take every figure from the regulation in force. Check competence and the register entry, both of which are quick and free.
This article offers professional orientation as at the date of verification. It replaces neither the regulations in force nor the assessment of a competent specialist.