Figure 4.4 Heat losses through the buildings` envelope

Figure 4.4Heat losses through the buildings` envelope

The three basic elements of a building envelope are the thermal barrier, air barrier, and water barrier, which altogether provide high-energy performance and highly comfortable indoor environment.

Thermal control layer

In Sustainable and Passive buildings the amount of insulation applied is commonly larger compared to conventional practices, however, it should be carefully calculated.

In achieving thermally high-performing envelop, the term ‘super-insulation’ can be met, commonly designating use of thick layer of insulation. However, this doesn't have to be always the case. The amount of insulation is dependent on the Form Factor, described in previous the chapter, as well as to the external surface area of the building. The larger the external surface area, the greater the thickness of insulation will be required and vice versa, less surface area relative to the floor area, would require less insulation.

Air and vapour control layer

An airtight barrier on the inside of the insulation has several purposes. At first it stops air (and heat energy) that is inside the building from escaping through uncontrolled gaps in the building envelope. This ensures air only goes in and out of the building in a controlled manner, by natural or mechanical ventilation.

The vapour control layer prevents moisture from inside the building getting into the building envelope where it might come into contact with a colder surface and condense. Where moisture does condense within the building envelope it increases the risk of mould and associated dangers, as well as the risk of damage to the building envelope.

This control layer also keeps the insulation dry and thus it preserves its performance.

A windtight barrier on the outside of the insulation is also required to preserve the performance of the insulation.