Thermal Bridging in window applications
What causes thermal bridging around windows? What are the most effective interventions to prevent and resolve it?
Eliminating thermal bridging around windows poses a significant challenge in energy-efficient design. Thermal bridges pose a threat to living comfort and the energy balance of homes, making it mandatory to find solutions during the design phase.
In this article, we delve into the issue of thermal bridging around windows and practical solutions to eliminate it, ensuring a more comfortable and sustainable living environment.
To ensure accurate analysis and precise verification of solutions, you can use a thermal bridge analysis tool, as demonstrated in the accompanying video.
Thermal bridge fixed in the center of a wall insulated from the outside with a flap
Contents
What Is a Window Thermal Bridge?
A window thermal bridge is a significant issue in building energy efficiency. This architectural flaw occurs when there is an imbalance between construction materials or when necessary precautions are not taken during window installation, resulting in heat or cool air leakage into the home due to a “cold” or “hot” spot that encourages airflow from outside to inside.
The lack of thermal insulation, such as in a concrete structure combined with brickwork or a steel structure with other materials, is the root cause of window thermal bridging. Resolving this issue involves restoring balance between construction elements. Mold and condensation, particularly common problems in homes, are often caused by the presence of thermal bridges around windows.
Therefore, careful attention to the correct installation of windows is essential, paying particular attention to all window components to create a perfect connection between the window element and the masonry, resulting in a building envelope free of thermal bridges.
Unfortunately, not all industry operators adopt necessary practices to ensure proper window installation, often simply fitting windows without sufficient attention to detail. Therefore, it is advisable not only to consider window prices but also to inquire about detailed installation procedures.
Thermal bridges around windows can be avoided or mitigated through carefully studied installation methods to achieve the perfect window opening renovation. This approach not only solves or prevents mold and condensation problems that negatively affect living comfort but can also contribute to improving building energy efficiency, leading to higher energy certification classes.
According to UNI 10818 and UNI 11673-1 regulations, the designer is responsible for selecting the type of window, identifying performance levels, and drafting the executive project for joints between the window and surrounding technical elements, paying particular attention to window fixing to the support, reducing thermal/acoustic bridges, and ventilating spaces. It is also important to evaluate morphological, dimensional, and physical compatibility between the window and surrounding elements, as well as conducting thermal analyses and condensation checks to ensure correct window installation and reduce thermal bridges.
Effects of a window thermal bridge
How to Eliminate a Window Thermal Bridge
As we have seen, the causes of thermal bridging can be manifold but can be (not always) predicted, studied, and therefore corrected and eliminated.
Eliminating or reducing thermal bridges around windows requires targeted intervention. There are several feasible solutions to address this issue, depending on the specific conditions of the building and windows.
Resolving Thermal Bridges Caused by a Pass-Through Sill or Threshold
One of the most common cases is the presence of a pass-through sill or threshold, where the marble slab or other material extends from the exterior to the interior, transmitting heat or cold from outside to inside the home. To solve this problem, it is necessary to interrupt the thermal bridge by cutting the slab and inserting insulating material between the two parts of the sill. This process, similar to that used for thermally broken windows with double glazing, ensures the separation of the two surfaces to prevent heat conduction.
Solutions for Thermal Bridges Caused by the Cassette
Another critical point is the cassettes, representing one of the most common thermal bridges in homes. When replacing windows with high-energy performance models, such as Class A, it is essential to also address cassettes to avoid thermal bridge formation. Replacing the cassette with a thermally insulated model or inserting adequate insulation is an effective solution to address this issue and prevent mold and condensation formation inside the structure.
Dealing with Thermal Bridges Caused by Metal Counterframes
The perimeter metal counterframe represents another critical point in terms of thermal bridges since iron is a good conductor of heat. In the presence of high-energy performance windows, the risk of thermal bridge formation is high. To mitigate this issue, it is advisable to replace the metal counterframe with a thermal structure or make a cut around the perimeter of the counterframe using specific tools. While this solution may improve the situation, it does not completely solve the problem but can help reduce its impact.
Correcting Balcony Thermal Bridges
Similar to windows, balconies can also be subject to thermal bridge formation due to the materials used and the lack of adequate insulation. To address this issue, it is possible to install an insulating system on the entire balcony facade or insert insulating elements. Thanks to technological innovations, such interventions can also be carried out on very old buildings, thereby improving energy efficiency and living comfort.
Material Selection Strategies to Reduce Window Frame Conductivity
The reduction of thermal conductivity in window frames largely depends on the choice of materials and their configuration within the profile. Metallic materials, such as aluminum and steel, have high thermal conductivity and therefore require specific corrective solutions; on the contrary, PVC, wood, and composite materials offer significantly lower conductivity values, making them more suitable for achieving high energy performance without particularly complex additional interventions.
An effective strategy involves adopting low conductivity (λ) materials or using multilayer composites that combine structural rigidity and thermal insulation. Multi-chamber PVC frames, for example, utilize internal cavities that reduce convective movements and improve longitudinal thermal resistance. Similarly, laminated wood frames benefit from the naturally low conductivity of the material, enhanced through impregnations and treatments that improve durability without compromising performance.
Hybrid materials such as wood-aluminum or PVC-aluminum profiles allow for a combination of aesthetics, robustness, and energy performance, provided there is effective separation of the metal parts through appropriate thermal barriers. Increasingly common are frames made of fiber-reinforced materials (FRP or GFRP), characterized by an excellent combination of mechanical stability and low conductivity coefficient, particularly suitable for high-performance buildings such as passive houses or NZEB.
The comparative analysis of materials must also consider parameters such as linear thermal expansion, torsional stiffness, and resistance to degradation, in order to ensure not only energy efficiency but also the stability and durability of the window system as a whole.
Integration of Thermal Break Technologies in Window Assemblies
The integration of thermal break technologies in window assemblies represents a fundamental step to reduce linear thermal bridges associated with metallic profiles. The thermal break consists of interposing a low conductivity element between the internal and external parts of the frame, interrupting the continuity of the high conductivity material and thus limiting heat transmission by conduction.
In aluminum windows, the most common solution is the use of insulating strips made of polyamide reinforced with fiberglass, characterized by excellent mechanical resistance and a drastically lower conductivity coefficient compared to metal. These strips are inserted between extruded metal shells and joined through mechanical rolling, generating a structurally monolithic profile but thermally decoupled. In some high-performance systems, wider or double strips are combined with additional insulating inserts made of polymeric foams or aerogel to increase the overall thermal resistance of the frame.
The effectiveness of the thermal break does not only depend on the conductivity of the insulating material but also on the geometry of the profile: internal air chambers, transverse webs, and multi-cavity configurations contribute to reducing conduction and convection paths. Advanced technologies include the use of aerogel in thin panels or closed-cell microstructures, capable of achieving extremely low λ values while maintaining reduced thicknesses.
In wood-aluminum and PVC-aluminum systems, the thermal break is often directly integrated into the profile design, where the external metal part serves as a protective coating while the internal part made of low conductivity material performs the main structural function. This natural separation significantly reduces the need for additional inserts while ensuring superior performance in the most severe climatic zones.
Finally, the implementation of an effective thermal break must be accompanied by careful control of the continuity between the frame and the wall node. Even with highly performing profiles, non-optimized installation or lack of complementary insulation at the joint can compromise the benefits of the technology, keeping linear losses (ψ) high. For this reason, the design of the thermal break must be integrated with the definition of the entire installation system, including vapor barriers, compressible insulating materials, and thermal expansion tapes.
Thermal Bridge Calculation
Below, I want to show you a video on the use of software for thermal bridge calculation, which facilitates identifying thermal bridges.
To learn more, read also:
The FAQs
What is a thermal bridge in a window?
The thermal bridge in a window is a point in the building envelope where there is an imbalance between materials or incorrect installation, causing heat or cold loss. The presence of a ‘cold’ or ‘hot’ element facilitates thermal flow between the interior and exterior, with risks of mold and condensation in the window opening.
What effects does a thermal bridge in a window cause?
Thermal bridges in windows can cause energy losses, deterioration of living comfort, mold and condensation formation, and a general increase in the building’s energy consumption.
How to eliminate or reduce the thermal bridge of a window?
To eliminate or reduce the thermal bridge, a properly designed installation is necessary. Solutions include: insulating passing thresholds with cutting and inserting insulating material; replacing or insulating the box; removing or modifying the metal frame; improving insulation in balconies; choosing low conductivity materials for frames and integrating thermal break technologies in window assemblies.
How to address a thermal bridge caused by a passing threshold?
To correct a passing threshold, it is necessary to interrupt the continuity of the material by cutting the slab (in marble or other material) and inserting an insulating element between the two parts. This prevents thermal conduction between the interior and exterior.
How to intervene on thermal bridges caused by the box?
Boxes represent one of the most frequent thermal bridges. To eliminate them, it is possible to replace the box with a thermally insulated model or add an adequate internal insulation layer, avoiding mold and condensation after replacing the fixtures.
How to reduce thermal bridges caused by the metal frame?
The metal frame is highly conductive. It can be replaced with a thermal frame or a cut can be made around the perimeter to reduce its continuity. This solution does not completely eliminate the problem but limits its impact.
Is it possible to eliminate thermal bridges in balconies?
Yes, the thermal bridge of balconies can be treated by applying insulating systems on the facade or inserting specific insulating elements. Modern technologies allow effective interventions even on older buildings.
What materials reduce the thermal conductivity of window frames?
Materials such as PVC, wood, composites, and fiber-reinforced profiles (FRP or GFRP) offer low thermal conductivity. Multi-chamber configurations or wood-aluminum and PVC-aluminum composites can also improve performance, provided there is adequate separation of the metal parts.
What does it mean to integrate thermal break in window assemblies?
The thermal break consists of inserting an insulating material (such as reinforced polyamide or polymeric foams) between the internal and external parts of a metal profile, interrupting heat transmission. In high-performance systems, aerogels and multi-chamber configurations are also used to further reduce conductivity.
Why is installation crucial for eliminating thermal bridges in windows?
Even with high-performance frames and materials, incorrect installation can maintain high thermal dispersion. It is necessary to ensure continuity between the frame and the wall node, integrating thermal expansion tapes, insulating materials, vapor barriers, and thermo-hygrometric checks to avoid condensation and energy losses.
