IDENTIFYING THERMAL BRIDGES   

Given the correct conditions, the main areas of thermal bridging within the building envelope can be identified using infrared thermal imaging. This technique can be used to take measurements from either inside or outside the building. Thermal bridges viewed from outside the dwelling can be identified by areas of high temperature, whilst thermal bridges viewed from inside the dwelling can be identified by areas of low temperature (see photographs below).

Thermal bridge at the junction between the ground floor and the external wall identified as an area of high temperature (red) on the thermal image. Caused by the ground floor slab extending across the cavity and meeting the outer face of the external wall.

Thermal bridges on the internal wall under stairs identified as areas of low temperature (blue) on the thermal image. Caused by the plaster dabs for the dry-lining.

In order to gain appropriate results, it is important that the infrared thermal imaging camera is used in the correct conditions. Measurements should be taken when the building is in a steady thermal state and a sufficient temperature differential must exist between inside and outside of the building. For instance, dwellings that are undergoing a coheating test provide a particularly good opportunity for identifying areas of thermal bridges, due to the consistent and large difference between the inside and the outside temperatures. If measurements are to be taken from outside the dwelling, then they should take place when the sky is overcast, or in the early morning. It is also important that the operatives have an appreciation of the type of construction that is being observed and the limitations of thermal imaging techniques when interpreting any images obtained. Various factors, such as service voids in timber frame construction, thermal bypassing effects, air leakage, direct sunlight and uninsulated primary pipework can have an influence on the images obtained.

The limitations associated with thermographic imaging are listed in detail in BSI (1999), and BSRIA (2002).