What Is Thermal Bridging?

A thermal bridge is an area or weak spot in the thermal envelope of a building where increased heat flow takes place. These points are also called cold bridges since they’re cooler than the surrounding areas. Thermal bridges create cold spots since heat always follows the path of least resistance when it escapes. 

Building materials have different thermal conductivity properties. Materials with higher thermal conductivity thus disrupt insulation, creating opportunities for heat transfer.

So, what is thermal bridging? It is the occurrence of thermal bridges or weak spots in the insulation of a building’s thermal envelope. With a compromised building envelope, you’ll experience inconsistent surface temperature and increased heat losses. 

Thermal bridging needs to be carefully considered when assessing thermal junction details by following recognised construction details in combination with PSI calculations. 

Continue reading to learn more about thermal bridges.

What Causes Thermal Bridges to Occur?

A thermal bridge does not occur spontaneously. There are several reasons why thermal bridges present themselves. Here are some key factors contributing to cold bridge occurrence in a building envelope: 

Material Thermal Bridges: A Gap in the Insulation Layer

Material thermal bridging happens when building materials with different levels of thermal conductivity form a junction or come into contact.

Metal and steel building elements are more susceptible to causing thermal bridges than their less conductive counterparts, like wood.  

One way to combat this is to pair more conductive materials with the correct insulation layer and introduce thermal breaks. They’re essential to limit thermal bridging occurrences and reduce air loss. 

A thermal bridge can also occur when there’s a gap between the insulation levels around windows and doors.  

Repeating Thermal Bridges: Interruptions in the Building Fabric

Thermal bridges also transpire where more conductive materials, like metal wall studs, bridge or pass through the insulation. If this occurs regularly throughout the element, you’re dealing with a repeating thermal bridge. This occurrence must be taken into consideration when calculating the U value of the element. 

Mortar joints or wall ties in masonry construction can cause regular interruptions in the building fabrics, giving rise to repeating thermal bridges. 

Geometric Thermal Bridges: Junctions Between Building Elements

These cold bridges occur when your heat-absorbing surface is smaller than your heat-emitting surface, perfectly demonstrated with building corners. The corner’s large emitting surfaces account for more heat flow opportunities, increasing heat loss. 

Geometric bridges, as the name suggests, depend on the geometry of the architectural design rather than the type of building material used. 

Point Thermal Bridges: Single-Point Penetration of the Thermal Envelope

Fixings, fastenings, screen brackets, and more can give rise to thermal bridges. These singular thermal bridges penetrate the thermal barrier in a specific spot of the building envelope. 

Now we understand why thermal bridges materialise, let’s discuss the effects of heat bridges on building projects.   

The Effects of Thermal Bridges 

Below is a list of potentially damaging effects your building could experience with the occurrence of a thermal bridge:

1. Reduced Energy Efficiency

The most common effect of thermal bridges is heat loss. The more severe the thermal bridge, the greater the level of heat loss. To reiterate, a bigger thermal bridge or more frequent occurrence of cold bridges leads to additional heat loss, decreasing your energy efficiency. 

Higher heat transfer levels will cause occupants to spend more money on energy to keep temperatures consistent. Heat can escape from the roof, floor, or wall, leading to increased spending on energy bills and consumption of resources.  

2. Compromising the Building Structure 

The building structure is an important aspect of an efficient building design. Thermal bridge points increase the opportunities for condensation to accumulate in homes and buildings. 

More than being points for heat loss, the temperature difference on account of cold bridging forms thick condensation — putting walls or interior surface structures at risk of moisture damage. Buildings could then deteriorate as structural elements experience mould, rot and damage, seriously risking your construction project’s long-term success. 

3. Reduced Air Quality

Thermal bridges cause decreased surface temperatures, allowing for moisture penetration. With a compromised building envelope, moisture droplets from the condensation create a premium environment for mould growth. Roof and wall areas are prominent areas where mould growth can take place. 

The severity of thermal bridges impacts insulation and can contribute to increased health risks that could otherwise have been avoided with proper thermal bridging considerations. 

How Do You Measure Heat Loss Through a Thermal Bridge?

The use of accredited construction details to measure thermal compliance has been outdated, and we now need to focus more on customisable and accurate PSI calculations.

A building’s thermal performance is represented by PSI values (also known as Ψ-values). Every stage of creating a building relies on accurate PSI values. With our helpful software, you can easily calculate the relevant PSI value (thermal bridging value) and identify areas of increased heat loss. 

However, it’s essential to understand how we get those values. Let’s take a deeper look at how to calculate a building’s thermal value. 

PSI Value Calculations

Linear thermal transmittance or the Ψ-value expresses heat loss associated with thermal bridges. Here’s a breakdown of how you can calculate heat losses for an entire junction:

  • Multiply the PSI value by the junction length. 
  • When looking at the results, the lower the PSI value, the lower the heat loss through the junction. 
  • To calculate heat loss through a thermal bridge, you should multiply the Ψ-value of each junction by its corresponding length.
  • Take this answer and calculate the sum of these values. 
  • Finally, when determining the overall percentage of building heat loss (Y-value), divide your previous answer by the total area of the external elements. 

How to Combat Thermal Bridges

The best way to address thermal bridging issues is to focus proactively on identifying possible thermal bridges in the design stage. 

Troubleshoot and try the following thermal bridging solutions:

  • Identify and remove or replace materials prone to creating a thermal bridge
  • Choose a less conductive material as an alternative
  • Alter your insulation thickness and placement, but ensure the installation plan fully matches the design brief
  • Only use the most effective insulation techniques
  • Focus on interrupting heat flow by identifying and reinforcing the path of least resistance 
  • To reduce energy consumption, you should implement thermal breaks to minimise thermal bridge occurrence and enhance energy efficiency.

It’s crucial that building designers are well-versed in thermal bridging to ensure ideal thermal performance. It also ensures better possibilities for meeting UK building compliance. 

The Importance of Thermal Breaks

A heat bridge can drastically increase overall building heat losses. In order to reduce aggressive heat flows through these bridges, thermal break materials need to be incorporated into the building design. 

According to Passive House Standards, thermal break materials do not allow thermal bridges to form, and they restrict air leakage. These breaks are essential to improving the efficiency of a building’s thermal envelope, in turn, optimising energy performance and reducing heat loss. 

Thermal breaks create true insulation continuity by creating a uniform thermal control layer. Simply put, these breaks keep the heat in while pushing the dew point out. By doing this, you “break” or disrupt the bridge. 

But using any scrap material for a break won’t do. To ensure it does its job, the material of an effective break needs to have lower conductivity levels than the junction you’re applying it to. Additionally, when attempting to complete a PSI value thermal bridge calculation, it’s vital to note that the thickness and area of the material should be considered.

AutoPSI: Fast & Accurate Thermal Bridging Calculations

Efficiently identify potential instances of heat loss with AutoPSI’s easy-to-use PSI value calculator. Our fully online thermal bridging software is created to help companies design more energy-efficient buildings with ease during the construction design stage.

With AutoPSI, you can access an accurate thermal bridge calculator that allows you to input the relevant thermal bridging details and leave the rest to our BRE-accredited thermal bridge calculation software. 

Our thermal bridge software solution allows you to create customisable junction details to streamline the calculations of your property developments. 

Interested in finding out how our thermal bridging software can help you identify thermal bridges? Request a free demonstration today to explore how our tool can help you.