All you need to know about thermal bridging

Why is thermal bridging an important consideration? Put simply; it will cost you more money to heat the property.


A thermal bridge is an example of heat transfer through conduction. It is also referred to as a 'cold bridge'. Thermal bridges in construction are the ‘leaky points’ of a building where heat escapes. The speed of heat loss depends on the materials’ thermal conductivity and the difference in temperature on either side of the thermal bridge. 

The heat loss associated with these thermal bridges is expressed as a linear thermal transmittance (Ψ-value) - pronounced as 'psi-value'.

The Conservation of fuel and power: Approved Document L (the building regulation in England setting standards for the energy performance of new and existing buildings) states that 'The building fabric should be constructed so that there are no reasonably avoidable thermal bridges in the insulation layers caused by gaps within the various elements, at the joints between elements and at the edges of elements such as those around window and door openings.'

 

Where does thermal bridging occur?

Thermal bridges occur mostly at junctions between two or more building elements. Common locations include:

  • door, window, floor and wall junctions
  • roof/ceiling-to-wall junctions
  • where studs or lintels meet an external surface
  • metal ties and concrete ‘snots’ in masonry cavity walls
  • where insulation has degraded or is under-specified, leaving cold spots (common with cavity wall insulation and slumped loft insulation)

Why is thermal bridging an important consideration?

Put simply; it will cost you more money to heat the property. Also, due to the difference in temperature, occupants may experience thermal discomfort near a thermal bridge. Recent research undertaken has shown that thermal bridging can be responsible for up to 30% of a dwelling's heat loss.
 

Condensation can also be a problem. When there is warm and humid air indoors, mainly in the winter, there is a risk of condensation in the building envelope due to the cooler temperature on the interior surface at thermal bridge locations.  If the relative humidity stays high enough for long enough then black mould will start to grow. Black mould feeds off the moisture in the air, so if the enviroment remains very humid, it is literally like watering a plant. These situations also result in poor indoor air quality. This, combined with black mould spores, poses certain health risks for occupants.


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