Up to 30% of heat loss in a building comes from thermal bridging alone. Choosing a popular insulation product from the market that performs well thermally is easy, but expecting the product to perform without thermal bridging may be the real challenge!
Thermal bridging seriously undermines the performance of a building – which is a significant problem, given how common it is. So, what is thermal bridging, and how can you avoid it?
What is Thermal Bridging?
Thermal bridging, also known as cold bridging, refers to the highest point of heat transfer within a building. The heat resistance in this section is much lower than its surroundings for multiple reasons, the most common being breaks in insulation. These breaks are often referred to as bridges and much like a bridge that allows you to cross water without getting wet, these thermal bridges allow heat to bypass insulation without being blocked. Which means, heat will pass much more easily into or out of the building.
Thermal bridges are common at junctions (wall-to-roof and wall-to-floor), corners, near openings (doors, windows, etc), and around pipe or cable holes. The complexity of construction, breaks in insulation around openings, and the limitation of some insulation materials are all common reasons for thermal bridging in these specific areas.
Types of Thermal Bridges
There are three main types of thermal bridges: repeating, non-repeating and random.
Repeating Thermal Bridges: As the name suggests, repeating thermal bridges occur at regular intervals across a space. This type of thermal bridging generally happens when insulation is bridged between timber or concrete studs, in a cavity wall for example, causing a break in insulation at every timber bridge.
Non-repeating Thermal Bridges: Non-repeating thermal bridges allow heat to escape faster than any other type. They only occur in specific areas that are less insulated than the rest of the building, such as the corners of doors and windows. This type of thermal bridging is often hard to avoid and can cause up to 15% of the overall heat loss across an entire building.
Despite being hard to avoid, non-repeating thermal bridges can be minimised through efficient design and clever construction measures.
Random Thermal Bridges: In most cases, a random thermal bridge occurs due to the presence of gaps or voids in the insulation layer, or from the use of a highly conductive material. For example, when you use steel frames, metallic fasteners, etc, these materials bypass the thermal insulation and create points of increased heat flow.
How Can Thermal Bridging Affect Buildings?
Thermal bridging can be especially problematic during winter, when heat loss is more rapid due to colder outside temperatures and stronger winds. In winter, these thermal breaks are the weakest points in a building’s insulation, allowing heat to escape twice as fast. This causes the indoor temperature to drop, increasing the need for heating and leading to higher utility bills, even with insulation.
What’s worse, this temperature difference doesn’t just lead to increased heating costs. Prolonged temperature differences, with warm and moist indoor air coming into contact with cooler surfaces, are the perfect conditions for condensation — leading to issues with dampness within the property.
Damp patches and water damage in houses with little to no insulation are often the result of these ‘normal’ condensation issues. However, thermal bridging can also lead to a more concerning issue called ‘interstitial condensation,’ which could occur within any layer of a building structure, walls, roofs, or floors, for example.
Interstitial condensation occurs when warm, moist air penetrates into the building materials and attaches to a layer of material that is below the dew point. The thing that makes this kind of condensation so insidious is that it happens inside of the building, where you can’t see it.
As it is not clearly visible outside, it can cause long-term damage without immediate warning signs. Over time this trapped moisture can lead to serious issues; such as mould growth, and degradation of the building materials, potentially compromising the structural health of the building.
In essence, thermal bridging doesn’t just risk damaging the performance of the building’s insulation, but its structural safety too. The more thermal bridges or breaks you allow in your insulation, the greater these risks will be. And that is without even touching on the impact these issues could have on the wellbeing and comfort of the buildings’ inhabitants!
How to Recognise And Measure Thermal Bridging?
If a property is suffering from thermal bridging, the early warning signs to spot are the following;
1. Temperature variations or cold spots on walls, ceilings, or floors that feel noticeably cooler than the surrounding surfaces.
2. Condensation, moisture buildup, damp patches or even mould growth
3. Higher than expected energy bills due to increased heating or cooling
4. Sagging or otherwise deformed areas of the building, which could be a sign of structural decay
5. Paint or wallpaper peeling away from areas of walls that seem dry on the surface
6. Persistent musty smells with no obvious dampness.
To measure the heat loss thermal bridging causes, you can rely on U-values and PSi Values (Ψ–values).
U-values represent the rate of heat transfer through a building component and are essential for assessing the overall insulation performance of those components. Lower U-values indicate better overall thermal insulation. For repeating thermal bridges, such as across studs, frames etc, the impact on heat loss is specific and can be measured within the u-value calculation itself.
Psi values, on the other hand, measure the rate of heat loss through junctions connecting materials of varying thermal conductivity, such as wall-to-floor or roof-to-wall connections. By multiplying the Psi-value by the length of the junction and adding up the sum total can give you the total estimated heat loss from the area (y value). Much like U-values, a lower Psi-value equals less heat loss through the junction, and therefore better insulation performance.
How Can Multifoil Insulation Prevent Thermal Bridges?
Continuous Insulation
If the insulation doesn’t flow continuously, due to the complexity of the construction, or due to the limitation of some insulation materials, exposed areas will have much lower heat resistance than its surroundings. However, if you opt for an insulation that’s designed to provide a continuous barrier over the building’s exterior, the problem is halfway solved already.
Multifoil insulation is an excellent example of continuous insulation. It consists of multiple, self-contained layers of reflective foil alternated with layers of insulating wadding to block all forms of heat transfer effectively. When installed correctly, multifoil insulation creates an even and unbroken thermal barrier, covering all potential gaps and cracks where thermal bridging could occur, such as at junctions and around structural elements.
Multifoil insulation is also great at keeping building elements — such as rafters, purlins, etc — protected inside the foil envelope from external weather, corrosion and other hazards.
Minimise Moisture Buildup And Condensation
Any insulation that absorbs moisture and loses performance over time is certainly not the right fit. Effective vapour control and breathable membrane insulation products help to prevent moisture from entering the building’s structural systems and causing condensation, protecting against structural degradation and other issues caused by moisture. Multifoil insulation with built-in vapour barrier layer thereby reduces air leakage and prevents cold air from bypassing the insulation.
Fill Gaps And Seal The Edges
Due to the flexibility and simplicity of installing foil insulation rolls, they can easily reach and wrap around junctions and corners without leaving gaps that would lead to thermal bridging later on. Using low emissivity tape, such as SuperFOIL Reflective Tape to seal and finish the edges after installation will further prevent any air leakage and heat loss.
Avoid Conductive Materials
When multifoil insulation materials that minimise all forms of heat transfer (conduction, convection and radiation) are used in conjunction with stainless steel fasteners, wooden frames, and pipe wrap insulation, heat conductivity can be controlled and so the temperature difference will be at minimum.
Talk to Our Experts Today!
If energy efficiency, building durability, and comfort are priorities, addressing thermal bridging is essential. By reducing the amount of bridged insulation, you can minimise the overall impact of thermal bridging and easily achieve industry-recognised building standards.
If you’d like to discuss potential solutions that can keep thermal bridges at bay, then get in touch with us today at [email protected] or 01636 555662.
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