Request a quote
Thanks for getting in touch
When designing a building, thermal bridges are the points where different materials meet, such as at junctions between walls and windows or floors and doors. These areas are prone to significant heat loss, which can reduce the overall energy efficiency of the building. This heat loss is referred to as linear thermal transmittance, Ψ (Psi) value, or cold bridges.
Optimising Building Efficiency and Reducing Heat Loss
Recent research has shown that thermal bridging can contribute to up to 30% of a building’s total heat loss. With each update to building regulations, thermal bridging has become increasingly important and will play a significant role in future iterations of the regulations.
The image below illustrates a thermal analysis of a balcony junction, where the cold (represented in blue) penetrates deeper into the wall construction through the metal structure. This creates a significant heat loss, contributing to higher energy consumption in the dwelling.
Why is Thermal Bridging Important?
Reducing thermal bridging is essential to meet the UK’s stringent energy efficiency standards. By addressing thermal bridges, you enhance a building’s overall energy performance and improve the long-term comfort of its occupants. This not only improves energy use but also supports the UK’s environmental goals, helping to reduce carbon emissions and meet sustainability targets.
How Are Thermal Bridges Calculated?
Thermal bridges are carefully measured and calculated as part of SAP (Standard Assessment Procedure) assessments. The process includes:
- Individual evaluation of each junction, such as windowsills, floor-to-wall connections, etc.
- Measurement of the length of each thermal bridge and calculation of the associated heat loss through these junctions
- Accurate assessment of the total energy loss from all thermal bridges, providing a clearer picture of the building’s overall thermal performance
By using bespoke, real-world calculations, developers can:
- Make significant improvements in energy efficiency
- Ensure compliance with building regulations
Example Thermal Bridge Calculation
The heat loss value associated with each thermal bridge varies based on the materials used.
An older metal lintel allows more heat transfer compared to a modern thermally broken version, while poorly constructed junctions, like where an internal floor meets an external wall, can create significant thermal bridges.
Changing the density of building blocks from heavy to lightweight can reduce heat loss (Ψ value) by up to 65%, as shown in the images below.
While standardised minimum values are available for calculation, these are based on worst-case scenarios. By calculating the actual heat loss through specific thermal bridge junctions, you can achieve more accurate results, leading to substantial savings in SAP assessments and an easier route to building regulation compliance.
How Can We Help?
Our expert guidance and thermal bridging analysis ensure your building’s energy performance is optimised and compliant with regulations:
- Bespoke Thermal Bridging Values: We provide tailored values specific to your project, offering more accurate performance assessments
- Carbon Emissions Reduction: Our team recommends strategies to reduce carbon emissions, ensuring your building meets SAP 10 compliance
- Cost-Effective Solutions: Bespoke calculations often offer a more affordable alternative to increasing insulation levels or altering construction materials
- No Planning Amendments Required: Improving thermal bridging usually doesn’t necessitate changes to planning or major structural modifications
- Long-Term Savings: Purchasing a full set of thermal bridging values for commonly used constructions can result in significant cost savings for future projects
FAQs
What is a thermal bridge?
A Thermal bridge occurs where heat escapes through junctions in a building’s insulation layer, typically at junctions, such as (but not limited to) wall-to-floor connections, window reveals, and roof edges.
Why are Thermal Bridges now so important?
In the latest version of SAP, SAP 10.2, thermal bridging junctions have greater importance and are therefore critical to the Part L (SAP) compliance.
By addressing thermal bridging early, designers can avoid expensive redesigns, lower carbon emissions, and often achieve Part L (SAP) compliance and potentially higher EPC ratings without additional renewables.
How much difference does thermal bridging really make?
A significant one.
Switching from default Psi-values to Recognised Construction Details (RCDs) can improve overall fabric efficiency by up to 50 %. Further improvements are possible with bespoke calculated junctions.
How are U-values and Psi-values connected?
Both measure heat loss — but in different ways.
U-values represent heat loss across a surface area (e.g. a wall or roof).
Psi-values represent heat loss along a junction or line (e.g. where wall meets floor, or at a window reveal).
How can I improve thermal bridging in my design?
A successful design maintains a continuous, unbroken insulation layer often called the thermal envelope.
Good practice includes:
Aligning insulation layers at junctions.
Avoiding materials that conduct heat (such as steel) through the envelope.
Using thermal breaks and high-performance junction details.
How do I know which Psi-values were used in my SAP assessment?
Your SAP report will list each junction, its Psi-value source, and whether it’s a default, accredited, or bespoke detail. A summary of Thermal Bridges used is often supplied alongside you SAP calculations, these can and should also include a schematic drawing of the junction.
What evidence of Thermal Bridges do I need for Building Control?
Part L does not specifically require evidence of thermal bridges used, however it is good practice to supply a separate thermal bridging report with the SAP report.
What simple design choices can hgelp improve thermal bridging calculation results?
Small design decisions make a big impact. Consider:
Thermally broken components – e.g. Catnic THERMAL or IG Hi-Therm lintels.
Lightweight or aerated blocks – reduce conductivity and improve U-values.
Simplified geometry – fewer corners and junctions mean fewer thermal bridges.
Integrated detailing early in design – retrofitting improvements after construction starts is difficult and costly.
Early coordination between designers, energy assessors, and contractors ensures thermal bridging performance is locked in from concept stage.
Are bespoke Psi-values worth the investment?
If you’re developing multiple plots or repeating a build type, having bespoke calculated junctions can improve EPC ratings across every unit while saving thousands on renewable add-ons.
It’s one of the most cost-effective upgrades for improving both compliance margins and long-term energy efficiency.
Can I use Thermal Bridge Calcualtions to improve my EPC rating on a conversion?
This is possible in some cases, conversions can be difficult to identify the existing construction in detail. Though in some case where say an internal timber frame is being installed, then yes Thermal bridging calculations can be an simple way to improve the EPC rating.
Benefits
- Tailored thermal bridging values specific to your project
- Simplified compliance process
- Avoid costly structural changes and material adjustments
- Enhance thermal performance, maximising energy efficiency and ensuring long-term savings
Start Your Thermal Bridging Analysis Today
Ready to optimise your building’s energy efficiency? Our experts are here to guide you through thermal bridging analysis and mitigation to ensure your project meets the latest regulations and delivers long-term savings.
Request a quoteCall to Discuss
