What Is Thermal Bridging? And Why Is It Important When Building a Passive House?
Building a passive house requires attention to detail, especially when it comes to minimising energy loss. Thermal bridges, or cold bridging, are areas where heat escapes more easily—typically found around windows, doors, and structural junctions. In order to meet the rigorous passive house standards, addressing every potential thermal bridge with proper insulation and sealing is essential. This helps retain warmth, enhances energy efficiency, and promotes year-round comfort.
At the core of passive house construction are five key principles that guide each phase from design to completion: Thermal Insulation, Ventilation and Heat Recovery, High-Performance Windows and Glazing, Airtightness, and Thermal-Bridge Free Design. In this blog, we’ll dive into the fifth principle—thermal bridging—exploring why it’s crucial for passive houses, where these weak spots commonly occur, and how to effectively prevent them.
Why Does Thermal Bridging Matter in Passive Housing?
Thermal bridging plays a critical role in passive house design. According to the Energy Saving Trust’s Thermal Bridging and Air Tightness report, ‘Around 30% of the total heat loss through a building’s fabric can be caused by thermal bridging’. This loss significantly impacts the performance gap between a building’s predicted and actual energy demand, leading to higher-than-expected energy costs for homeowners. By rigorously eliminating thermal bridges, passive houses offer a solution that enhances energy efficiency and reduces unnecessary expenses—making them a smart, long-term investment in sustainable living.
Where Do Thermal Bridges Commonly Occur?
To design a truly thermal-bridge-free passive house, identifying common weak points is essential. Thermal bridges typically fall into five main categories:
Repeating thermal bridges – These occur where regular interruptions break the continuity of the thermal envelope, such as at mortar joints, studs, or wall tiles.
Non-repeating (linear) thermal bridges – These arise from irregular gaps in the insulation layer, often found around openings like windows, doors, loft hatches, roof and floor junctions, and internal walls.
Geometrical thermal bridges – These result from the shapes and contours of a building’s design. Areas with a high external surface area relative to internal volume, such as external corners, roof-wall junctions, window reveals, and floor-to-wall junctions, tend to have greater heat loss.
Material thermal bridges – These occur where materials with different thermal conductivity meet. Examples include metal fasteners, columns, and window frames.
Point thermal bridges – These are single penetrations in the thermal envelope, providing a direct path for heat to escape. Typical examples include balconies, chimneys, and beams.
Understanding and addressing each of these categories is crucial for achieving an efficient and thermally secure passive house design.
How Do You Prevent Cold Bridging?
Preventing Thermal Bridging in a Passive House requires careful design and the implementation of best practices to avoid creating linear or repeat point thermal bridges. Key methods include:
Timber I joists, also known as TJI Joists, are an economical choice for reducing the overall U-value of the building structure. With their minimal thermal bridging properties, they can lower U-values by up to 15% compared to traditional joists, offering improved insulation.
By applying these best practices, a passive house can significantly reduce thermal bridging, enhancing both energy efficiency and the comfort of its occupants.
For passive housing, triple-glazed windows with insulated frames are required. To meet Passivhaus, windows should have a U-value of 0.80W/(m²K) or less, ensuring minimal heat transfer and greater indoor comfort. To achieve the Passive House standard, having glass that is triple-glazed is not sufficient on its own – the frames need to be specially designed to be thermally broken.
Using thermal bridge-free foundation systems, such as insulated raft foundations or thermal break plates, will help to prevent cold from entering the base of the structure. These systems ensure a continuous insulation layer from the ground up, essential for maintaining the thermal integrity of the building.
The building envelope needs to have a continuous layer of high-performance insulation, whether that is an external wrap or created within the building fabric itself. How you create this continuous layer, whilst also achieving a building’s structural requirements and without creating substantial Thermal Bridging, is the key to good Passive House design – there is no ‘quick fix’, it requires a great deal of thought and attention to detail.
Common choices for insulation in Passive Houses are glass and mineral wool, known for their excellent thermal resistance and fire-retardant properties. Whilst PIR and XPS/EPS can be used, the practical application is difficult as cutting these products on-site inevitably leads to air gaps on installation (particularly in the walls).
Minimise Thermal Bridging With The Help Of Tŷ Eco
Addressing thermal bridging is vital to achieving the energy efficiency and comfort that define passive house design. Thermal bridges can lead to significant heat loss, driving up energy costs and affecting indoor comfort. By prioritising solutions for thermal bridging from the start, you’ll be well on your way to meeting rigorous passive house standards.
If you’re considering a passive house project, consult with our team of experts. With our experience in passive house design and construction, we can guide you through minimising thermal bridges and creating a home that’s both efficient and comfortable.
