Velux GGU INTEGRA Instrukcja Użytkownika Pobierz pdf (Strona 100)

Building physics

100 VELUX

Underfelt

UNVENTILATED UNDERFELTS

Unventilated underfelts are based on diusion open materials

that are positioned directly on the insulating material. The small

amounts of moisture that via diusion through the vapour barrier

percolate through from the interior of the building to the roof con-

struction continue through the underfelt material. From here the

moisture is removed by the ventilation under the rooﬁng material.

As diusion is not by far as eective as ventilation, it is very

important that the vapour barrier is absolutely airtight. The diu-

sion capacity of the underfelt is not sucient to compensate for

leakages in the vapour barrier.

VELUX underfelt collar BFX is made of diusion open material and

can thus be used for unventilated underfelts. The method for ﬁtting

the underfelt collar is the same for ventilated and unventilated

underfelts.

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Velux GGU INTEGRA Instrukcja Użytkownika Strona 100