Thermal Performance of Building Envelopes
The thermal efficiency of a building is a function of the thermal performance of the planar elements (e.g. wall, roofs, windows), the local heat losses that can occur around the planar elements and where the planar elements are penetrated by the building components that conduct heat. These areas of high local heat flow, commonly known as thermal bridges, can have a significant impact on the thermal performance of the building envelope and the building energy consumption.
As part of a thermal assessment of the building envelope, it is recognized that the local heat losses, due to penetrations or similar local effects, have to be calculated and where necessary minimized so that the thermal efficiency of the building envelope is within acceptable limits.
Thermal bridges can be identified using thermal imaging cameras. The thermal bridges will appear as areas of higher temperature when viewed from the exterior of a building. This is shown in Figure 1 where higher temperatures (i.e. thermal bridges) around the door, window and balcony slab can be seen due to higher heat transfer through the assemblies.
Figure 1: Thermal image of a residential building with higher temperatures at the windows, doors and balcony slabs
Figure 2 shows a well insulated balcony, as there is a low outside surface temperature at the slab, coloured in blue, due to minimized heat transfer through the assembly.
Figure 2: Thermal image of a residential building with minimized thermal bridges and an even temperature distribution along the envelope