Thermal bridging is weakness in the envelope of the building that allows heat to pass through more easily. These weak points form a bridge between the inner and outer façade, making the building less energy efficient. These generally occur when there’s a gap in the insulation or at junctions between different elements (e.g. between the wall and window). Some materials like steel studs also act as thermal bridges, more heat flow through steel than any other mineral fibre of insulation of the same thickness.

Thermal bridges cause increased heat loss and can account for 20-30% of a buildings heat loss which can offset the thermal benefits of insulation. They can also lead to condensation build-up or mould growth in the building.

Types of thermal bridging

Repeating

Occur when there are regular interruptions in the building fabric (for example studs or wall ties).

Linear (non-repeating)

Usually occur at junctions (for example around windows and doors or where walls and floors penetrate the thermal envelope).

Geometric

Occur where the external heat loss area is greater than the corresponding internal area of the envelope (for example corners).

Point

Typically, these are due to fixings or fasteners, brackets for a canopy in a rainscreen, a flue passing through a wall, or isolated steel beams or columns.

How can thermal bridging be prevented?

• Removing materials causing the bridge from the design.

• Changing materials causing the bridging to ones which are less heat conductive.

• Varying the thickness or placement of insulation.