Vapour barrier
A vapour barrier is a layer of material impermeable to water vapour, which prevents the migration of the vapour (coming from both the building materials and the rooms and spaces below the roofing) through the insulation where it may condense, spoiling the thermal characteristics of the insulation and in many cases originating deterioration. The use of the vapour barrier is always advisable when thermal insulation on a roof is required. The choice of the type of material must be made according to the type of substrate and the hygrothermic conditions of the environment. When the underlying relative humidity exceeds 80% at 20 °C, the use of a product with zero permeability to vapour is suggested. The 3 mm thick NOVALL-I is the membrane which fulfils this requirement, being reinforced with a 0.07 mm thick aluminium foil coupled with a 50 gr/sqm fibreglass. With lower relative humidity, a fibreglass reinforced membrane such as 3 mm thick VELOBIT is sufficient. The choice of the application method depends on the type of substrate and should be either non-bonded or semi-bonded.
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