The frame has transverse arches spaced apart in its lengthwise direction and mounted on side-rails comprising front, middle and rear sections hinging together. Each rail is a profiled extrusion (140) comprising a main body (142-149) and a flange (156) extending from a base (146) to form a slot (164) between them. An external C-section channel (158) is formed on the outside of the flange and secures a window-seal. A wedge-shaped insert (166) fitting in the slot adjusts to flange angle and thus the position of the seal in relation to the roof. The inset can be in brittle sections joined together, those (g,h) outside the slot being broken off after angle adjustment.
