1. The largest open question
According to professional assessments one question weighs more than the others, and it is not a technical detail. It concerns transposition of the directive.
The draft's largest question mark is the use of total primary energy in calculating the energy performance value, in place of the former non-renewable primary energy. The difference lies in how renewable energy is treated in the calculation.
| Basis of calculation | Effect |
|---|---|
| Non-renewable primary energy | rewards the use of renewable energy more strongly |
| Total primary energy | counts all consumption, whatever its source |
Results on the two bases are not directly comparable, which affects every calculation made to date. According to professional sources, worked examples for an Estonian nearly zero-energy apartment building have been used to illustrate the problem, which indicates the effect is significant.
2. The timetable for the cost-optimal methodology
The second open question concerns where the limit values come from at all. The basis of the calculation has not been published.
According to professional sources the European Commission undertakes to update the cost-optimal methodology by 2026, and calculations under the new methodology are to be made in 2028. The new methodology should work equally well for energy and emission performance, reflect the price of carbon dioxide adequately, and take account of health effects, including the financial effect of improved indoor and outdoor air quality.
Calculations made under the current methodology therefore remain valid for some years yet, and the next major change is known as a principle. According to professional sources the directive stresses that the nearly zero-energy building requirements remaining in use until 2030 must rest on earlier cost-optimal calculations.
3. What it means in practice
Three consequences, and the third concerns documents that end up in an archive. They last long after the project.
The current limit values are not final, but they will not change in the coming months either. A change of calculation basis affects results more than an adjustment of limit values, because it changes what the figure means rather than only how large it is permitted to be.
Comparing earlier calculations with new ones therefore requires knowing the methodology, not merely the date. This affects existing projects whose documentation is read years later.
4. Why it is worth knowing
Three reasons, all practical, and the third holds for this guide as a whole. They explain the cautious wording.
A promise given to a client must allow for the fact that the bases change, and when planning a long-term project it is useful to know the direction of travel. Professional credibility further requires that an open question is not presented as settled: what has not been decided must not be presented as certain.
5. What this guide does not do
Two limits follow directly from the above. The guide does not state numerical limit values for zero-emission buildings, because they depend on transposition, and it does not predict which basis of calculation will finally apply. Both are available in the legislation in force, once adopted, and must be checked there.
Summary and four practical rules
The draft's largest open question is the use of total primary energy in place of non-renewable, which changes the weight of renewable energy in the calculation and makes earlier results not directly comparable. The European Commission updates the cost-optimal methodology by 2026 and new calculations are made in 2028, while the nearly zero-energy requirements remaining in use until 2030 rest on earlier calculations. The current values are not final, but they will not change in the coming months either.
Four rules: distinguish the settled from the unsettled when explaining matters to a client. Record the methodology used alongside the calculation, not only the date. Allow for a change of calculation basis in a long-term project. Do not predict final values, but name what is open.
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.