Velux GGU INTEGRA Instrukcja Użytkownika Pobierz pdf (Strona 99)

Building physics

VELUX 99

Underfelt

VENTILATED UNDERFELTS

Ventilated underfelts are made of diusion tight materials. The

moisture is removed from the roof construction as the cavity

between insulation and underfelt is ventilated with fresh air.

The air circulation under a ventilated underfelt may be obstructed

in one or more roof sections when a window is installed. To ensure

ventilation in the roof section aected, it is recommended either:

• to t ventilation pieces in the underfelt material (1) or

• to establish ventilation holes at the top of the rafters (2), so that

air can ﬂow to/from the adjoining roof section.

This must be done both above and below the window.

The lack of a ventilation path below the underfelt may result in

accumulation of moisture in rafters and insulation material. This

may reduce the performance of the insulating layer and cause rot

damages.

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Velux GGU INTEGRA Instrukcja Użytkownika Strona 99