The Ministerial Decree 28.10.2025 (new Minimum Requirements Decree, in force, as we have seen, from 3 June 2026) introduces a substantial change in the energy assessment of buildings, significantly modifying the checks on the building envelope. This is not a simple update of the performance limits, but a revision of the very logic with which these checks must be addressed.
The system is no longer unique, but structured on multiple levels, depending on the extent of the intervention. The designer is therefore called upon to move within a complex framework, in which each check represents a different degree of in-depth analysis.
Understanding how the checks on the building envelope change with the new decree is essential to avoid interpretative errors and correctly set up the energy design.
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Classification of interventions and logic of building envelope checks
The checks are applied depending on the type of intervention:
- new construction and demolition/reconstruction;
- major first level renovation;
- major second level renovation;
- energy requalification;
- extensions and similar cases.
It is important to underline that this classification is not new, but derives from the previous Ministerial Decree of 06.26.2015. The new decree therefore does not change the categories of intervention, but substantially redefines the system of associated checks, making it more consistent with the complexity of the intervention.
Checks on the building envelope: from component to system
The Ministerial Decree 28.10.2025 introduces an increasing level of three prescriptive checks:
- transmittance of the current section Outc;
- average transmittance Umed;
- global heat transfer coefficient H’T.
These checks represent progressive levels of analysis:
- from the evaluation of the stratigraphy alone;
- to the consideration of thermal bridges;
- up to the overall reading of the building.
Usc: verification of the stratigraphy
The transmittance of the current section Usc represents the most immediate level of verification. It considers exclusively the stratigraphy of the building element, without including thermal bridges or discontinuities. The calculation is based on the sum of the thermal resistances of the layers, including surface resistances.
Applies to:
- energy redevelopments;
- major second level renovations.
Umed: the role of thermal bridges
The Umed average transmittance, already present in the Ministerial Decree of 06.26.2015, introduces a reading more in line with the construction reality. In addition to stratigraphy, consider the contribution of thermal bridges and geometric and structural discontinuities. The novelty of the Ministerial Decree 10.28.2025 is that the limit values to be respected incorporate tabular thermal bridges within them.
Applies to:
- major second level renovations.
Thermal bridges in the reference building
A particularly relevant aspect introduced by the Minimum Requirements Ministerial Decree 2025 concerns the explicit presence of thermal bridges also in the reference building. They are modeled through standard linear transmittance tabular values, contained in Table 5-bis of Appendix B.
There are five types considered:
- sill;
- shoulder;
- architrave;
- box-window;
- balcony.
If there is a thermal bridge belonging to one of these types in the real building, it will also be present in the reference building. However, if in the real building there is a thermal bridge that cannot be traced back to these typologies, it will be considered in the model of the real building, but will not be present in the reference building.
The modeling of thermal bridges therefore becomes crucial, since it directly affects the configuration of the reference building and the limits to be respected.
H’T: the global heat transfer coefficient
The global heat transfer coefficient H’T represents the most advanced verification among building envelope checks. It expresses the weighted average of the transmittances of the entire envelope, including opaque and transparent components and taking into account the geometry of the building.
Applies to:
- new buildings;
- major first level renovations.
A coherent progression of checks
The system of checks on the building envelope follows a clear progression:
- Energy requalification → Exit check
- Major level II renovation → Usc + Umed checks
- Major level I renovation and new construction → check H’T
The latter are accompanied by checks on energy needs:
- EPH,nd for heating;
- EPc,nd for cooling.
The role of RED III and Legislative Decree 5/2026
The transposition of the RED III directive through Legislative Decree 5/2026 introduces further design constraints. In fact, for major second level renovations the following is envisaged:
- the obligation to cover at least 15% of primary energy needs for heating and cooling through renewable sources and the integration of systems for the production of energy from renewable sources, including the installation of photovoltaic systems.
It may therefore no longer be sufficient to intervene only on the building envelope.
Conclusions
With the Ministerial Decree of 28.10.2025 the transition is clear: the integrated casing-system design is no longer an option, but a necessity. The new regulatory system imposes a change of approach, in which checks on the building envelope cannot be addressed in isolation, but must be read within a coherent and complex system.
New challenges arise for technicians, which include:
- full awareness of the tests to be mastered;
- knowledge and correct modeling of thermal bridges;
- the ability to integrate casing and system right from the early design stages.
This is a complexity that requires continuous study and constant updating.
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