As the importance of energy-efficient home construction gains momentum in the UK, the spotlight is increasingly focused on creating dwellings that are not only environmentally friendly during construction but also throughout their lifespan. Understanding and addressing thermal bridging in building design stands out as an essential aspect of the key strategies to achieve this goal.
Thermal bridging, a phenomenon that interrupts the continuity of insulation and promotes heat loss, is a critical factor to consider when aiming to construct a low-energy, eco-friendly home.
This article will delve into the fundamentals of thermal bridging, its impact on energy efficiency, and strategies for preventing it, tailored specifically for self-builders aspiring to create their dream eco homes.
THE DEFINITION AND IMPACT OF THERMAL BRIDGING
Thermal bridging (or cold bridging) refers to areas within a building envelope where heat is more readily conducted through the surrounding materials. This can lead to increased heat loss and compromised insulation effectiveness. In a low-energy home, where every effort is made to create an insulated envelope, thermal bridging disrupts the thermal barrier, decreasing overall energy performance.
By investing in insulation, self-builders are essentially attempting to create a snug, warm “blanket” around their home, which can be compromised by thermal bridges. These bridges can manifest in various ways, such as timber studs in a timber frame construction or structural steelwork in more complex designs.
Thermal bridges tend to form at junctions where building elements meet. As heat seeks the path of least resistance, these areas become conduits for heat transfer, making the interior space less comfortable and energy efficient.
CAUSES AND EFFECTS OF THERMAL BRIDGING
Factors leading to thermal bridging are often tied to building materials and design choices. Construction methods like timber frames, while popular for their versatility, can introduce potential thermal bridges due to the lower thermal performance of wood compared to insulation.
There are many negative impacts of thermal bridging. Not only does it compromise the energy efficiency of the home by increasing heat loss, but it can also lead to increased energy consumption. Residents may find themselves cranking up the heating to counteract the cold spots caused by these bridges. Moreover, condensation can form around these areas, potentially leading to mould growth and affecting indoor air quality and occupant health.
HOW THERMAL BRIDGING IS MEASURED
U-values are a crucial measure of thermal conductivity and play a pivotal role in assessing a building’s energy efficiency. Thermal bridging directly influences U-values, as any interruption in the insulation envelope can lead to higher overall values, indicating decreased efficiency.
Low-energy homes aim to achieve superior U-values, which can be compromised by the presence of thermal bridges. To illustrate, traditional construction methods might allow for higher U-values due to less rigorous insulation integration, while low-energy homes prioritise minimising U-values to ensure optimal performance.
To measure thermal bridges, a PSI value is used, calculated through specialised software by a consultant. This is distinct from U-value calculations, which are more straightforward. Specialist consultants like ourselves at AC Architects offer PSI calculations as an additional service. When designing a low-energy home, engaging with a structural engineer from the start and having a design team familiar with thermal bridging is crucial. While common sense and building regulations can help reduce thermal bridging, site-specific calculations are needed to precisely determine its extent.
For example, Passive House standards require thorough PSI calculations, especially for complex designs involving materials like steel. Even if not aiming for Passive House certification, addressing thermal bridges is essential to prevent condensation, maintain comfort, and reduce energy consumption.
IDENTIFYING AND MITIGATING THERMAL BRIDGES
Self-builders must collaborate with their design team to identify potential thermal bridging areas during the design phase itself. Addressing these areas early on allows for informed design decisions that avoid potential pitfalls. Structural engineers play a critical role in providing guidance on preventing thermal bridging, especially in areas where steelwork or other structural elements might intersect with the building envelope. Also, if you come to the design process with a preferred construction method, we can work around it to avoid thermal bridges.
During the construction phase, attention to detail is paramount. Contractors must be well-versed in the intricacies of thermal bridging prevention. Each junction, corner, and intersection require careful consideration to ensure that the insulation envelope remains intact. Additionally, on-site verification through thermal imaging and construction quality checks is essential to catch any potential thermal bridging oversights before they become long-term issues.
When considering features like large window openings, it’s important to be aware of potential thermal bridging areas, such as lintels and supports. Strategies to mitigate thermal bridging include designing features that balance your requirements without sacrificing insulation integrity. While we don’t want to compromise your design, we can guide you to minimise the impact on thermal bridging.
As architects, we can provide a cold/thermal bridging package during the production information stage, which involves detailing the key elements of your build that require special attention to prevent thermal bridges. This might involve using higher-performance insulation materials in specific areas, ensuring the insulation is properly installed to reduce heat transfer across thermal bridges.
High-performance insulation materials play a crucial role in reducing heat transfer across thermal bridges. Different insulation materials have varying thermal conductivities, which affects their ability to retain heat within the building. For instance, materials like wood fibre insulation have lower thermal performance compared to materials like PIR insulation. Using the right insulation material can help achieve the desired levels of insulation without compromising the building’s thermal envelope.
To learn more about selecting the right form of insulation, click here.
PREVENT THERMAL BRIDGING THROUGH FABRIC FIRST
To ensure a cost-effective transition to low-carbon heating, the adoption of a ‘Fabric First’ approach. This approach prioritises the fundamental elements of construction for energy efficiency rather than focusing solely on technologies.
Embracing the fabric first approach means constructing a home that boasts exceptional thermal performance and a strong focus on airtightness. This approach leverages site orientation and solar gain while incorporating a ventilation strategy that promotes a healthy indoor environment.
- Strategic Orientation – Long elevations with ample south-facing windows harness solar gain.
- Passive Solar Gain and Shading – Passive strategies prevent overheating and optimise thermal mass utilisation.
- Optimal Insulation and Airtightness – High levels of insulation within an airtight envelope minimise energy loss and eliminate thermal bridges.
- Intelligent Layout – Daytime spaces are thoughtfully positioned to the south, with utility areas to the north.
- High Spec Glazing – Window specifications enhance energy efficiency and indoor comfort.
- Mechanical Ventilation Heat Recovery Systems (MVHR) – Incorporating the MVHR system contributes to the overall effectiveness of the design.
Central to this concept is thermal bridging-free construction, forming one of the six fundamental principles of low-energy building design. Eliminating thermal bridges is pivotal in ensuring optimal performance from your chosen construction method and building design.
PASSIVE HOUSES AND THERMAL BRIDGING
The Passive House standard is the pinnacle of energy-efficient design and construction, and it places significant emphasis on eliminating thermal bridging. Airtightness, super insulation, and high-performance windows are integral to Passive House principles, all of which contribute to minimising heat loss and thermal bridging. Achieving the Passive House standard necessitates a holistic approach, including thorough detailing, careful material selection, and precise execution.
By adhering to Passive House principles and considering the specifics of thermal bridging prevention, self-builders can achieve remarkable levels of energy efficiency, comfort, and sustainability in their homes. While the strict criteria of the Passive House standard might not be feasible for everyone, the underlying principles can guide self-builders in making informed decisions that minimise heat loss and enhance overall performance.
Whether aspiring for the Passive House standard or simply aiming to build a low-energy home, tackling thermal bridging from the outset is vital, and there are a few simple ways to do this. Gain an understanding of the causes of thermal bridging. Additionally, invest in quality materials that will work to create a high-performance home. Engaging with a knowledgeable design team is never a bad idea, too.
With careful planning, collaboration, and attention to detail, you can prevent thermal bridging with ease.
