Thermal Bridge Calculations

A thermal bridge (sometimes referred to as a cold bridge) is an area or component of a building construction that has a higher thermal conductivity than materials surrounding it, creating a path of ‘least resistance’ for the transfer of heat. Typically, thermal bridging can account for up to 30% of a buildings heat loss. Within the thermal envelope of a building, thermal bridges are typically be divided into the following:

Repeating Thermal Bridges

These bridges are repeated at intervals across construction elements e.g. steel wall ties, mortar joints or timber joists. Such bridges are typically assessed within a U-Value calculation.

Non-Repeating Thermal Bridge

These bridges occur intermittently at points within the construction. They are usually caused when there is a discontinuity within the thermal envelope e.g around window or door openings, when balconies penetrate through external walls, or at junctions, where ground floors meet external walls. These are sometimes expressed as Psi Values or with the symbol

Within the regulations, there is a requirement for the insulation envelope of any heated building to be designed and constructed to limit heat loss through thermal bridging. Failure to do this can lead to issues such as:

• The formation of cold spots leading to mould/growth and condensation due to the reduction of surface temperatures.
• A reduction in air quality, impacting the health and wellbeing of occupants due to the growth of mould spores.
• The degradation of building components due to the increased risk of interstitial condensation within structural elements.
• An increased likelihood of cold draughts, causing thermal discomfort for occupants.
• Expensive remedial costs to rectify any issues caused by excessive cold bridging.

At SK/AD, we have qualified staff who can model and assess construction details to limit the risk of condensation and reduce heat loss between fabric elements.

For larger developers, with multiple construction details, we can provide a full suite of relevant details for the use in SAP or SBEM calculations. These bespoke calculations often improve upon the Default Psi Values or Accredited Construction Details, provided by the UK Government, which in turn reduces the requirements for other products such as renewable technologies.