Thermal regulation, thermal bridges and technical solutions

As buildings become better and better insulated, thermal bridges have an ever-greater impact on heat loss. To limit or eliminate them, technical solutions exist that are constantly evolving. This is the case, for example, with thermal bridge breakers, the subject of this article.

The higher the insulation performance of a wall, the greater the losses caused by thermal bridges. Caused by discontinuities between materials, and between materials and the wall, thermal bridges become the only points through which heat can pass to the outside, generating losses in addition to the surface losses of the walls.

It's worth noting, for example, that in a building insulated to BBC (Bâtiment basse consommation) standard, which is the minimum level required by the thermal regulations currently in force in France, thermal bridges can account for more than half of all losses, excluding ventilation. This is not a new problem, however, and all professionals, contractors and project managers alike, are well aware of the need to reduce these leaks. In fact, this has become a mandatory requirement for all new buildings, as thermal bridges must be treated.

It should also be noted that, over and above regulatory compliance, the treatment of thermal leaks also ensures the comfort of occupants, by avoiding the sensation of cold, and the durability of the building against pathologies such as the risks of cracking, mould, condensation and corrosion at thermal bridges, inside the building itself.

A special feature of France, unrivalled in any other European country, is the practice of insulating from the inside out. The lining complex, an insulation panel generally finished in plaster and placed inside buildings, is very widespread in France. Obviously, this type of insulation creates more thermal bridges with singular points, than insulation from the outside; the latter being common practice elsewhere in Europe and even the world.

Apart from France, only Japan, South Korea and Turkey use interior insulation.

This article first reviews the evolution of French thermal regulations, before detailing the aspects specific to the regulations currently in force, the RT 2012 standard. It then explains what thermal bridges are, and describes the concepts of hygrometry and moisture transfer.

In order to make the reader aware of the mistakes that should not be made, yet are all too common, a few examples of ineffective solutions are then highlighted. Solutions that really deal with structural thermal bridges are then detailed, and the article concludes with an examination of simple calculation methods that can be used to dimension thermal bridge breakers.