Types of Thermal Bridges in Buildings
Different types of thermal bridges have various implications for the thermal performance of buildings.
Thermal bridges are junctions in the building or insulation layer that facilitate faster heat transfer and loss. This reduces the effect of insulated building materials and increases opportunities for condensation and mould growth.
Read on to learn more about thermal bridging, examples of thermal bridges, and how to combat them.
What is Thermal Bridging?
Each piece of building and insulation material has its own thermal transmittance or thermal conductivity levels (represented by U-values). Materials with higher U values have higher thermal conductivity rates.
Thermal bridges or cold bridges occur when heat follows through the path of least resistance and moves from a warm spot to a cold spot — lowering the temperature of the interior surface. This, in turn, creates a temperature difference that can reduce the efficiency of the building’s thermal envelope.
These weak spots in the building envelope promote more heat transfer between the inside of the building and the outside. The heat loss can result in the formation of condensation, which leads to mould growth. Additionally, increased heat loss leads to the need for increased energy consumption to compensate.
Identifying the Types of Thermal Bridges
Thermal bridges are most likely to occur on the floor, at wall junctions, corners, and around windows and doors. They are most commonly caused by disrupted thermal insulation or building construction issues.
Depending on the type of thermal bridge, they can be potentially damaging to a building’s thermal performance in different ways. Some thermal bridge examples include:
Material Thermal Bridges
These occur when the building materials have different thermal conductivity properties and come into contact with each other. The material with a higher thermal conductivity increases the heat flow. An example of this is when steel anchor bolts pass through the insulation. This allows for additional heat loss compared to the surrounding areas.
Examples: The use of metal fasteners, certain structural elements like a column, and implementing window frames.
Repeating Thermal Bridges
Repeating thermal bridges occur when evenly distributed interruptions in the thermal envelope follow a regular path. This is a significant thermal bridge that usually gets integrated into the building fabric during construction on account of continuously using materials with a higher thermal conductivity than the insulation materials around it.
Examples: Heat loss is usually higher where there are wall ties in masonry walls, studs in timber or metal frame constructions, and mortar joints.
Linear Thermal Bridges
These thermal bridges occur when gaps, discontinuities, or disturbances exist in the insulation layer or building envelope. As opposed to repeating thermal bridges, these occur at a certain thermal junction where the insulation is disrupted. We can use linear thermal transmittance (ψ) to calculate the energy loss occurring at linear thermal bridges.
Examples: This type of thermal bridge occurs around window and door openings, loft hatches, roof junctions, internal walls and floor junctions.
Geometrical Thermal Bridges
Geometric bridges do not occur entirely because of building materials. Instead, they arise due to the layout or design of the building structure. This means that the shape or geometry of a building can affect heat transfer by presenting more space for it to occur.
Examples: This type of thermal bridging occurs at external elements like corners, edges and junctions.
Point Thermal Bridges
These are single penetrations in the building envelope, creating a direct path for heat flow from the inside to the outside of buildings. This kind of thermal bridging only occurs in one spot. To quantify energy loss levels occurring as a result of point thermal bridges, we look at point thermal transmittance (χ).
Examples: Steel balconies, fastening elements, flues and chimneys, and different building elements like beams or stanchions.
How to Address Different Types of Thermal Bridges
It’s essential to understand how to combat all types of thermal bridging that can occur. In doing so, building designers can improve energy efficiency by reducing the heat flow out of the building envelope, which can lead to many other benefits.
Here is a look at how to approach various thermal bridges:
Linear Thermal Bridges
Here are a few key ways to mitigate the effects of a non-repeating or linear thermal bridge:
- Improve insulation techniques by introducing special insulation materials or techniques between different building elements.
- Prevent the formation of thermal bridges with careful building design and detailing procedures that minimise direct paths for heat transfer.
- Incorporate thermal breaks in window and door frames to increase the thermal resistance of the building fabric.
Geometrical Thermal Bridges
Combat increased energy consumption and the appearance of cold spots by:
- Maintaining insulation coverage across all junctions and in tricky geometric areas.
- Making innovative design choices like avoiding sharp corners between windows and wall junctions.
- Implementing thermal breaks in external projections and balconies to reduce thermal bridge occurrence and difference in the surface temperature.
Point Thermal Bridges
To decrease the risk of mould growth and increase energy efficiency, here are some steps to help avoid point thermal bridge occurrence:
- Ensure that flues, pipes, and cables are fully insulated.
- Increase the usage of thermal breaks around the penetrations in the form of special grommets, pipe collars, or insulation backing plates.
- Properly seal around penetrations during construction to reduce heat flow and air loss.
Material Thermal Bridges
When addressing material cold spots, building designers can:
- Choose materials with similar thermal properties.
- Improve techniques or methods around insulated structural elements to mitigate heat transfer.
- Apply appropriate design modifications to remove extending structural elements from the interior to the exterior.
Repeating Thermal Bridges
To reduce repeating heat loss, consider:
- Enhancing the building’s structural design by reducing the paths for direct heat flow and thermal bridge occurrence in the design phase.
- Implementing thermal breaks by placing materials with lower thermal conductivity within the structure to reduce heat flow.
- Improving thermal performance with continuous external insulation over the studs or wall ties that can lead to a thermal bridge.
- Making use of specialised software to identify and address potential thermal bridge occurrences before construction.
AutoPSI: Combat Thermal Bridges with Accurate Thermal Modelling Software
Thermal performance was initially only calculated using U value calculations, which only accounts for heat loss through a wall, roof or floor.
With part L of the newest building regulations introduced, just using Y value and U value calculations is no longer sufficient to pass SAP ratings. PSI values also need to be calculated for a more comprehensive insight into projected thermal performance. However, manually calculating PSI values can be tedious and leaves room for error.
With AutoPSI, you can simplify and streamline calculating heat losses in various junctions by creating customisable junction details. Accurate PSI value calculations contribute towards a reduced performance gap and help avoid having to overcompensate elsewhere to pass the SAP test. Our thermal modelling tool is fully online, fast, BRE-accredited, and meets ISO requirements.
Identify and mitigate thermal bridging challenges during the design stage with accurate and fast PSI value calculations. Sign up for a free demo of our PSI value software today.