Thermal bridges are parts of the building envelope where more heat is lost than elsewhere. Heat loss through thermal bridges can account for more than 30 % in unfavourable cases.

The main consequences of thermal bridges are:

• an increased thermal energy requirement due to cooling via the thermal bridges
• lower surface temperature on the inside of the wall
• condensation in this area, leading to mould developing

Three different types of thermal bridge can be distinguished:

1. The so-called geometrical thermal bridge is due to a discrepancy between the inside and outside surface area of an external wall (e.g. at the corner of the building), whereas the rest of the building element is implemented uniformly.
2. A material thermal bridge occurs where more than one type of material is used in a structure. A simple example is a horizontal fire barrier with a different thermal conductivity incorporated in a composite thermal insulation system.
3. Structural thermal bridges occur for example because of structural requirements applying to a building element, e.g. a reinforced-concrete pillar in single-shell insulating masonry.

It should also be noted that linear thermal bridges generally occur at edges, connections and junctions, but spot weaknesses can also occur, e.g. at anchor points for curtain walls, canopy roofs, balconies, etc.

1. Rule of avoidance: wherever possible, do not penetrate the insulating envelope.
2. Rule of penetration: if penetrating the insulation envelope is unavoidable, the resistance to heat transfer within the insulation layer should be as great as possible. This may mean using high-strength insulating materials, for example consisting of solidified foam insulation. Alternatively, the cross-section can be kept as small as possible and implemented in a high-strength, low-conductivity material, e.g. stainless steel anchors instead of aluminium.
3. Rule of junction: at junctions between building elements, merge insulation layers without gaps (transition over the whole area).