Thermal bridges and thermal performance of buildings

In the construction sector, the assessment of the thermal performance of the building envelope is often associated with parameters such as the thermal transmittance of building components. However, practical experience shows that the actual behaviour of a building depends not only on the characteristics of individual elements, but also — and above all — on the quality of construction details.

What is a thermal bridge?

Thermal bridges are one of the most critical aspects in the assessment of the building envelope. Their impact on key parameters such as thermal transmittance and thermal resistance makes it essential to adopt an approach that considers not only the declared performance of individual components, but also their actual behaviour once integrated into the building system.

Thermal resistance and thermal transmittance: what do these parameters indicate?

Thermal resistance (R) represents the capacity of an element to resist heat flow, while thermal transmittance (U-value) describes the amount of energy passing through a building component per unit area and per unit temperature difference.

These parameters, determined on homogeneous elements, make it possible to assess the performance of building components under ideal conditions. In actual construction practice, however, the continuity of the building envelope is interrupted by junctions, material changes and geometric nodes. At these discontinuities, thermal resistance decreases locally and thermal transmittance increases, generating more intense heat flows compared to surrounding surfaces.

As a result, the overall performance of the building envelope may significantly differ from the values predicted during the design phase.

Thermal bridges: effects on comfort and durability

The consequences of thermal bridges are not limited to increased energy losses.

The reduction in internal surface temperatures can create favourable conditions for the formation of surface and interstitial condensation, with the consequent risk of mould growth and material degradation phenomena. At the same time, localised thermal discomfort may occur due to radiant asymmetry or the presence of colder surfaces compared to the surrounding environment.

These aspects directly affect indoor environmental quality, the durability of structures and the building’s compliance with the thermo-hygrometric comfort requirements increasingly demanded by current regulations.

UNI EN ISO 10211 and advanced aalculation methods

The analysis of thermal bridges requires tools capable of realistically representing the behaviour of construction nodes.

In this context, the UNI EN ISO 10211 standard introduces calculation methods based on finite element method (FEM) numerical simulations, allowing professionals to:

• assess the distribution of heat flows within construction details;
• determine specific parameters such as linear thermal transmittance (ψ-value);
• analyse internal surface temperatures for condensation risk assessment purposes.

The use of these tools makes it possible to overcome the simplifications of traditional models and bring theoretical assessments closer to the actual behaviour of the building, through a mathematical model supported by results in the form of isotherms and heat flow lines.






 

Example of a corner made with a wood-cement insulated concrete form (ICF) block with internal insulation – modelling and results

The italian regulatory framework: when thermal bridge assessment is required

Thermal bridge assessment is not only considered good design practice, but is also explicitly required under the current Italian regulatory framework.

In particular:

• Legislative Decree 192/2005, implementing the EPBD Directive, establishes the general criteria for the energy performance of buildings and delegates the definition of calculation methodologies to implementing decrees;
• Ministerial Decree of 26 June 2015 (the so-called “Minimum Requirements Decree”) requires energy performance assessments to be carried out according to the relevant technical standards, including UNI/TS 11300, which provide for the evaluation of the contribution of thermal bridges through analytical or numerical calculation in compliance with UNI EN ISO 10211 or UNI EN ISO 14683;
• the update introduced by the Ministerial Decree of 28 October 2025 (effective from 3 June 2026) further strengthens this approach by introducing the explicit assessment of thermal bridges in the reference building for new constructions, demolitions and reconstructions, and major renovations of the first level;
• for hygrothermal purposes, the verification of the absence of condensation and mould risk is required with reference to UNI EN ISO 13788, with particular attention to building envelope junctions.

In light of this framework, an accurate thermal bridge assessment becomes an essential step for the preparation of the technical report pursuant to Italian Law 10, for verifying compliance with minimum requirements, and for the correct energy classification of buildings.

Thermal bridges assessment: from design to installation

Issues related to thermal bridges often arise at the interfaces between systems: window-to-wall connections, structural element junctions and insulation system discontinuities.

For this reason, thermal bridge management cannot be delegated to a single phase of the process, but requires an integrated approach involving design, manufacturing and installation. In thermal bridges assessment, boundary conditions and the actual installation methods of systems also play a decisive role.

The definition of effective construction details and their correct implementation are therefore key elements in ensuring continuity of performance under real operating conditions.


The effects of thermal bridges on the building envelope: mould and condensation

Services offered by Istituto Giordano

In this context, the Institute, through its Heat Transfer Laboratory | Calculations division, is able to support designers, manufacturers and industry professionals through an integrated range of technical services, including:

• numerical analysis of thermal bridges using finite element calculations in accordance with EN ISO 10211;
• determination of linear thermal transmittance values (ψ-values) and internal surface temperatures;
• condensation and mould risk assessment in support of hygrothermal requirements;
• support in the design of construction details, including comparative evaluation of alternative solutions.

The integration of advanced calculation methods and laboratory expertise enables the Institute to provide concrete support throughout the entire supply chain, from product development to in-service performance verification.

Today, rigorous thermal bridge analysis represents an indispensable tool for designing buildings that are more energy-efficient, comfortable and compliant with current regulations.