Imagine standing barefoot on a tiled floor in winter – that sudden chill you feel underfoot perfectly illustrates the concept of thermal bridging. They create pathways for heat to escape our buildings, leading to energy waste and potential structural issues. Recent studies suggest that thermal bridges can account for up to 30% of a building’s heat loss, making them a critical consideration in modern construction and renovation.
In this comprehensive guide, we’ll explore what thermal bridges are, why they matter, and most importantly, how to address them effectively. Whether you’re a homeowner, architect, or simply interested in building science, understanding thermal bridges is crucial for creating energy-efficient, comfortable, and sustainable buildings.
What are Thermal Bridges?
To understand thermal bridges, let’s first consider a basic principle of physics:
heat always moves from warmer to cooler areas, seeking equilibrium.
A thermal bridge is an area in a building’s envelope where heat flow is different compared to the heat flow through the surrounding elements. This typically occurs where materials with different thermal conductivities meet or where there is a discontinuity in the insulation. Simply said,
thermal bridges are places in the building envelope through which heat can escape easier.
The physics behind thermal bridging is straightforward but significant. Materials conduct heat at different rates, measured by their thermal conductivity, also called lambda value illustrated as ‘K-value’ or ‘λ-value’ and it is measured in W/(mK) [Watts per meter Kelvin]. The higher the value the higher the heat losses and lower the surface temperatures! When we use highly conductive materials that penetrate the insulation or if parts of the building envelope are less insulated, we inadvertently create superhighways for heat transfer and paths for heat to bypass the insulation in a building’s thermal envelope.
Examples for lambda values of common building materials are:
- Aluminium – 160 W/(mK)
- Steel – 50 W/(mK)
- Stainless steel– 17 W/(mK)
- Reinforced concrete – 2.3 W/(mK)
- Wood – 0.13 W/(mK)
- Mineral wool insulation – 0.031 – 0.052 W/(mK)
From this it becomes evident that aluminium which has a lambda of 160 W/(mK) conducts heat more than 1200 times better than wood which has a lambda of 0.13 W/(mK) and even more staggering that aluminium conducts 4000 times more heat compared to common insulation materials which have lambda of around 0.04 W/(mK).
To quantify the impact of thermal bridges, we use the psi-value (ψ), which measures the additional heat flow caused by the thermal bridge compared to the surrounding undisturbed elements. A higher psi-value indicates a more significant thermal bridge, meaning more unwanted heat loss or gain. If the psi-value is below 0.01 W/(mK), the detail is considered thermal bridge-free, ensuring minimal energy loss and improved overall building performance.
Now let’s get a bit more practical and compare 3 wall types with 20cm insulation – a wall with steel studs, with timber studs and an undisturbed wall assembly. The steel studs even though they are only 2 mm thick, are causing a massive thermal bridge with a lambda of 0.21 and the overall U value of the assembly is 0.50 W/(mK). The timber studs (6x20cm) also cause a thermal bridge but much smaller with a lambda of 0.04 W/(mK) and an overall U-value of the wall 0.24 W/(m2K). For comparison – the wall without the thermal bridges has a U-value of 0.18 W/(m2K).
All in all, the steel profiles increase the U-value of the wall by 178% and the timber studs only by 33% due to the thermal bridges caused by these materials.
The 3 main types of Thermal Bridging:
- Structural thermal bridges: occur where building elements like steel beams or concrete columns penetrate the insulation layer.
- Geometric thermal bridges: form at building corners or joints where the external surface area differs from the internal surface area.
- Material-induced thermal bridges: happen when materials with different thermal conductivities penetrate the insulation material, such as metal fasteners penetrating insulation boards.
The Impact of Thermal Bridges
The consequences of thermal bridging extend far beyond simple heat loss. In a typical modern home, thermal bridges can increase heating costs by 20-30%, but their impact reaches deeper than just energy bills. Consider the comfort implications: thermal bridges create cold spots on interior surfaces, leading to uneven temperatures throughout a space. You might notice this as a cold zone near an exterior wall or window, even when your heating system is running full blast.
More concerning is the risk of condensation. When the warm and humid indoor air meets a cold surface created by a thermal bridge, it can condense into liquid water. Over time, this moisture accumulation can lead to mould growth, deteriorating air quality, and even structural damage. In severe cases, this can compromise the building’s integrity and create health hazards for occupants.
From an environmental perspective, the increased energy consumption caused by thermal bridges directly translates to a larger carbon footprint. In an era where building sustainability is crucial, addressing thermal bridges becomes not just an economic consideration but an environmental imperative.
Where Thermal Bridging occurs?
Thermal bridges can be found in numerous locations throughout a building, often hiding in plain sight. Window and door frames represent one of the most common thermal bridging sites, where old metal frames (unless they have thermal breaks) can create a direct thermal connection between interior and exterior environments. These areas often reveal themselves through condensation on windows during cold weather.
Balcony connections present a particularly challenging thermal bridge in apartment buildings. Traditional balcony slabs that extend from the interior floor structure create a massive thermal bridge, essentially acting as a cooler that draws heat from the building. In the example below, the thermal bridge has a psi-value of 0.74 W/(mK) – 74 times higher than for thermal bridge-free design.
Other common places where thermal bridges occur are junctions between walls, floors, and roofs, the installation thermal bridge around window and doors, penetrations through the insulation layer, such as structural beams or utility pipes, etc. Even seemingly minor penetrations, like mounting brackets for exterior ventilated facades or insulation fasteners, can create significant thermal bridges if not properly detailed.
Preventing and Addressing Thermal Bridges
The most effective way to address thermal bridging is to prevent it during the design stage. This requires detailed thermal bridge calculations to assess potential weak points in the building envelope. Advanced software tools, like flixo, allow architects and engineers to model heat flow and optimize construction details before the building is even built. By eliminating or minimizing thermal bridges in the design phase, energy efficiency and occupant comfort are significantly improved, reducing the risk of condensation and mould growth.
For existing buildings, thermal imaging cameras can help identify some thermal bridges by visualizing temperature differences on the surface of walls, ceilings, and floors. This is particularly useful for spotting areas of heat loss and locating problem zones that contribute to discomfort and increased energy use.
Solutions
Addressing thermal bridges requires different approaches for new construction versus existing buildings. In new construction, the focus should be on prevention through thoughtful design. This includes specifying thermal breaks for balconies, using insulated window frames, and carefully detailing junction points between different building elements.
For existing buildings, solutions range from simple to complex. Adding exterior insulation can help minimize the impact of structural thermal bridges, though this may not be practical or permitted in all situations. Interior insulation can also help, but requires careful consideration of moisture dynamics to avoid creating new problems.
Going back to the example with the balcony connection – modern construction often employs thermal break technology to address this issue and the thermal bridge can be reduced down to a psi-value of around 0.08 W/(mK). Using thermal breaks in retrofit projects, however is not an option and then the best way to tackle the thermal bridge is to use flanking insulation which reduces the thermal bridge value more than two times down to 0.30 W/(mK)
Innovative materials and technologies continue to emerge in the battle against thermal bridges. Thermal break materials, which provide structural support while minimizing heat transfer, have become increasingly sophisticated. High-performance windows now incorporate multiple chambers and thermal breaks within their frames to reduce heat loss.
Cost-effective solutions for homeowners might include sealing gaps around windows and doors, installing insulated covers for attic hatches, and ensuring proper insulation around utility penetrations. While some thermal bridges may require professional intervention, many can be addressed through DIY efforts.
Conclusion
The future of construction will likely bring even more innovative solutions for thermal bridging, but the principles remain constant: identify the paths of heat loss, understand their impact, and implement appropriate solutions. By addressing thermal bridges, we not only create more comfortable and efficient buildings but also contribute to the broader goal of reducing our environmental impact.
To master thermal bridge calculations and learn how to optimize them in the design phase, explore our Thermal Bridges Masterclass. For a deeper dive into energy efficiency, consider our Certified Passive House Designer/Consultant Course!
