Air and vapour barriers

To avoid uncontrolled air exchange and heat losses through building encloses, it is essential to take care of the functional barriers of the building. In our latitude, buildings need a wind barrier, a heat barrier or heat insulation and an vapour barrier.

A high-quality airtightness of the building prevents the outflow of warm air from the building. In recent years, the regulations on requirements for airtightness of buildings have become tougher in all countries.

Wind barrier

A wind barrier on the outside of the building acts as a shield against the effects of wind and external moisture on the building structures. It provides a one-way moisture movement – from the structure of the building to the outside.

Vapour barrier

The building’s vapor barrier protects structures of the building from the inside by holding up wet indoor air. For good overall airtightness of the building, seal all connections:

  • corners,
  • walls at ceilings and foundations,
  • air and vapour barriers between window sills and door thresholds,
  • crossing electrical installations and pipes,
  • chimneys.

Heat insulation and building airtightness separate the outdoor climate from indoor climate. The temperatures of these two climates are equalised by air flow. In winter, the warm indoor air moves outward through the structural elements of the building. Vapour barriers stop this air flow, thereby reducing heat losses. At the same time, the indoor is not completely isolated, as in the thermos, but the air exchange will continue through the diffusion process.

Condensate formation

If the air flow through heat insulation layers is uncontrolled, the insulation may cool more rapidly at certain points. The closer to the outside wall of the building, the greater the possibility of condensate formation. Condensate can cause serious damage to the structure of the building and other layers of heat insulation. Load-bearing structures may lose their endurance and individual heat insulation layers may stop performing their functions.

Important to note!

Modern airtightness solutions for buildings are becoming more and more sophisticated, so there is a need to develop continuity in heat insulation and airtightness at the beginning of the design stage.

When planning and introducing airtightness of the building, do not forget the following basic principles:

  • Use simplified shapes to minimize the number of joints and connections.
  • Design the vapour barrier line at the design stage and see that it is followed during construction.
  • Select a high-quality air and vapour barrier with a high value of Sd (water vapour resistance diffusion-equivalent air layer thickness).
  • Install vapour barrier connections with a 100-200 mm overlap and seal with tape.
  • The vapour barrier must be continuous on both wall-to-wall and wall-to-ceiling joints. These joint areas are complex and require special attention.
  • For the air and vapour barrier to be long-lasting, it should be correctly attached to the surface.
  • If wiring or distribution boxes pass through the air and vapour barrier, they must be carefully sealed.
  • If ventilation or other pipelines pass through the air and vapour barrier, they must be carefully sealed.
  • The area of foundation-to-wall joints must be insulated by a capillary barrier that prevents moisture from rising up through the foundation and reaching the walls.

Quality assurance tests

It is recommended that the pressure test method be used to check the airtightness of the building. The Blower door test determines the airtightness of the building. The Blower door test of the building can accurately determine the heat resistance of the building and detect air leakage places that are not otherwise detectable.

Unlike with a thermographic survey, reduced and increased air pressure is created in the room by the Blower door test. This allows for simulation of wind exposure and the difference between indoor air pressure and outdoor pressure at the same time on all sides of the building. A smoke generator is also used for the detection of defects without a thermal chamber, which allows for the detection of complex air flow trajectories and leakage/supply places. A clear advantage of the Blower door test is the possibility of identifying defects also during warm weather without waiting for low outdoor air temperature!

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