Why is there a vapor barrier in the house and why is it better to install it by winter?

How does the vapor barrier work?

If the humidity in the house rises, it delays moist vapors and prevents them from penetrating into the facade or roofing pie. Excess moisture is absorbed by the rough surface of the film. When the air becomes drier, it evaporates and is removed by ventilation.


The vapor barrier prevents moisture from penetrating to the insulation, structural materials of walls and roofs.


As part of the facade system, it provides:


protection against condensation of moisture and wetting of the insulation, if the dew point falls inside its layer. The dew point is the space inside the wall where cold outdoor and warm air coming from the room "meets". In the presence of water vapor, moisture condenses in this space;

dryness of wooden elements of the wall, crates. The tree does not crumble, it does not warp and does not lead;

protection of metal fasteners, elements of subsystems and other structures from corrosion. Metal parts cool down faster when the temperature drops, and condensate falls on them first.

As part of the roofing system, the vapor barrier protects against:


wetting, deformation, increasing the thermal conductivity of the insulation layer;

the appearance of mold, fungus on the surface of wooden rafters, crates.

Why is it better to install a vapor barrier by winter?

In summer, the house is better ventilated, and the temperature inside and outside is about the same. Condensation of moisture inside the enclosing structures does not occur. In winter, when the rooms begin to heat, the temperature difference between outdoor and indoor air can reach 40-50 ° C. If wet vapors fall on the dew point, condensation falls out.


Specialists of the company "Vestmet" note that this is especially dangerous when using mineral wool insulation. When moistened, the fibers in its structure stick together, there is no air left between them, and it deforms, shrinks. Its thermal conductivity increases several times.


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