Vapour-permeability is a kind of a bulkhead construction ability for permeating water vapour that penetrates through it from a building’s inside to the outside. The parameter is formulated in g/m2/24h, which stands for the gram number of water vapour that a particular bulkhead is able to permeate. As far as our products are concerned, a roof membrane or foil is able to penetrate 1m2 in the time of 24 hours. Proportionately high vapour-permeability prevents against building up excessive moisture quantities in a roof bulkhead and protects the roof against changes responsible for lowering its parameters, what, in consequence, can even lead to its damage. Apart from all that, due to the use of vapour-permeability there is no need for keeping any venting slot between a roof membrane and thermal insulation. Moreover, it counteracts its excessive cooling down, what in turn has a positive influence on the costs reduction of energy used for heating a building.
• The WDD unit is [g/m2/24h].
• WDD is a relative value.
• WDD is dependent on the air temperature, air humidity and atmospheric pressure.