Method of applying a foil on an inclined roof structure

A method of applying a foil on an inclined roof structure, wherein the inclined roof structure comprises a ridge beam, a gutter extending parallel to the ridge beam, a plurality of parallel roof bars interconnecting the ridge beam and the gutter and a ventilation opening frame which surrounds a ventilation opening that is located between the ridge beam, the gutter and two neighboring roof bars, wherein the method comprises:

• supplying a window frame which is complementary to the ventilation opening frame and fits inside the ventilation opening frame,
• introducing the window frame within the ventilation opening frame and holding the window frame at a fixed position with respect to the ventilation opening frame,
• laying a foil onto the inclined roof structure such that it extends at least from the ridge beam to the gutter and covers at least the neighboring roof bars,
• fixing the foil to the window frame and the ventilation opening frame along respective circumferential edges thereof,
• cutting the foil between the window frame and the ventilation opening frame, hence forming the window frame including the foil.