Glass façades place high demands on both architecture and engineering. They must provide daylight, transparency and a light façade expression, while at the same time meeting increasingly strict requirements for energy performance, indoor climate and durability. In this context, thermal bridges are one of the most important issues to address systematically.

For consultants and engineers, the challenge rarely lies in the basic principle itself. Most are aware that heat flows towards the weakest parts of the building envelope. The difficulty arises in the interfaces where façade systems, the structural frame, brackets, glazing assemblies and installation meet. These are precisely the areas where thermal bridges typically occur, and where they often have the greatest impact on U-values, condensation risk and the overall operational performance of the building.

In façade projects, it is therefore not sufficient simply to select a façade or window system with good laboratory values. The real performance is largely determined by the details.

A thermal bridge is an area in a construction where heat flows more rapidly than through the surrounding building elements. In glass façades, this typically occurs when a material with high thermal conductivity connects the exterior and interior, or when the insulation layer is interrupted at a junction.

The consequence is not only increased heat loss. Thermal bridges also reduce the internal surface temperature. When the temperature drops sufficiently, the risk of condensation increases, which in some cases may lead to moisture-related problems, reduced thermal comfort and poorer indoor environmental conditions.

For consultants, this means that thermal bridges should be considered as more than just an energy issue. They are also a matter of function, durability and user comfort.

Typical thermal bridge zones in façade projects

In practice, certain areas repeatedly prove to be critical.

1. The connection between façade and floor slab

The junction between the glass façade and the slab edge is a classic thermal bridge zone. Here, concrete, steel, fixings, fire stopping, insulation and façade profiles often meet in a compact detail where space is limited and requirements are numerous.

Problems typically arise when the slab edge has not been coordinated with the façade principle from the outset. If insulation is interrupted or compressed, or if there is direct contact between internal and external material layers, linear heat transmission can increase significantly.

At the same time, this detail must accommodate other requirements, including fire protection, tolerances, installation access, movement accommodation and water management. For this reason, the slab edge detail often becomes a compromise if it is not properly addressed early in the design phase.

The technical point is simple: even a façade with good centre-of-glass values can have significantly poorer overall performance if the slab edge connection is not optimised.

2. Brackets and structural fixings

Brackets and support brackets are necessary to transfer loads from the façade to the building’s structural frame. However, they are also among the most critical thermal bridges, as they are often made from steel or aluminium and therefore act as efficient heat conductors.

In many façade projects this effect is underestimated, particularly when brackets are treated as secondary components rather than as an integrated part of the building envelope’s thermal performance. A bracket may be structurally necessary, but from an energy perspective it can become a weak point if it penetrates the insulation layer without sufficient thermal separation.

The risk is greatest in projects involving heavy façade elements, large cantilevers or complex installation principles where brackets increase both in size and number. In such cases, the cumulative effect of many small thermal bridges can become significant.

It is therefore important to consider:

• minimising the number of through-fixings

• optimising bracket geometry and positioning

• using thermally broken brackets where possible

• documenting the bracket’s contribution to overall heat transmission

3. Spacer bars in insulated glass units

The edge of the glazing unit is another critical area. While the glass surface itself may have a low Ug-value, the edge zone is strongly influenced by the spacer bar and the interaction between the glass, edge seal and frame profile.

Traditional metal spacer bars can create a significant thermal bridge along the glass edge. This reduces the internal surface temperature and locally increases the risk of condensation. In practice, it is often at the edge of the glass where the first signs of condensation appear on cold days with high indoor humidity.

For this reason, the choice of warm-edge spacers and the overall design of the glazing edge is important. This is particularly relevant in systems with slender profiles and large glass panels, where an elegant architectural expression is desired without compromising thermal performance.

HansenMillennium has been developed to replace older steel window systems with solutions that address issues such as thermal bridging and insufficient insulation while maintaining very slim profiles. The system can be supplied with both double and triple glazing, and technical documentation demonstrates the energy performance of different window configurations depending on glazing specification and build-up.

Impact on U-Values

When assessing glass façades, it is important to distinguish between individual component values and overall performance. A low Ug-value for the glass does not necessarily mean a low U-value for the entire façade element.

The overall U-value is influenced by:

• the performance of the glazing

• the thermal properties of the profiles

• the glazing edge zone

• linear thermal bridges in junctions

• fixings, brackets and connections to the structural frame

For this reason, two façade projects using the same glazing type may perform very differently in practice. The decisive factor is how the details are resolved.

With prefabricated façade solutions, part of the advantage is that details can be developed, repeated and quality-controlled under more controlled conditions. Hansen Group Ltd, for example, develops modular façade systems designed with high levels of insulation, low weight and a focus on energy performance and spatial efficiency, while digital design tools are used to ensure transparency in energy calculations and technical detailing.

Condensation risk is often the first sign

In many projects, thermal bridges are not first identified through energy calculations but during operation. Building users may experience cold zones near the façade, draught sensations or visible condensation at glass and profile junctions.

Condensation occurs when the surface temperature drops sufficiently relative to indoor humidity. Thermal bridges are therefore critical even when they do not significantly affect the calculated energy balance. Local temperature reductions alone can create problems.

For consultants, it is also worth remembering that condensation risk is not limited to extreme winter conditions. It may also occur in buildings with high internal moisture loads, fluctuating ventilation rates or spaces with high occupant density. Therefore, assessments should always be made in relation to the building’s intended use.

How can thermal bridges be reduced in practice?

The short answer is that thermal bridges cannot be eliminated through a single product choice. They are reduced through consistent detailing and coordination.

Early coordination between disciplines

The most important decisions are made early. When architects, engineers, façade contractors and suppliers work together on façade principles from the outset, it becomes possible to resolve junctions before they are constrained by structural design, module dimensions and fire requirements.

Focus on junctions rather than system data alone

Good system data is necessary but not sufficient. Junctions at slabs, plinths, spandrels, window interfaces and brackets must be analysed as individual details. Both linear heat loss, installation principles and potential temperature drops should be considered.

Reducing through-metal components

Where possible, the number and size of through-brackets should be limited and solutions with thermal separation should be used. Even small improvements can have a significant impact when repeated across an entire façade.

Improved glazing edge zones

The choice of spacer bar and the correct integration between glazing and frame are crucial. In large glazing areas and slender profiles, the edge zone becomes particularly important because the thermal bridge represents a larger proportion of the overall performance.

Precision in installation

Even a well-designed detail can lose effectiveness if it is poorly executed. Tolerances, compressed insulation, incomplete sealing or incorrectly positioned brackets can significantly reduce thermal performance. Design and installation are therefore closely connected.

System design and detailing

From the perspective of Hansen Group Ltd, work on thermal bridges does not begin with the final energy calculations. It begins with system design and with the details that connect façade, window, structural frame and installation.

Three main approaches are particularly relevant.

First, systems are developed to address common issues such as thermal bridges and insufficient insulation found in older solutions.

Second, prefabricated façade principles are developed with high insulation performance and digital design processes.

Third, strong emphasis is placed on detailing, installation guidance and technical support throughout the project.

It is precisely this combination that holds much of the potential. Thermal bridges are most effectively reduced when system selection, detailing and installation principles are considered together from the start.

Thermal bridges in glass façades rarely occur in the large façade surfaces themselves. They occur in the junctions – at slab edges, brackets, glazing edges and in the interface between what has been designed and what is ultimately built.

For consultants and engineers, the key lesson is therefore that thermal bridges should not be treated as an add-on to façade design. They are an integral part of façade performance. When addressed early and systematically, it becomes possible to improve U-values, reduce condensation risk and create more robust façade solutions.

A well-performing glass façade is therefore not only a matter of transparency and aesthetics. It is also a matter of well-designed details.