The purpose of rooflight GVT is to provide roof access for craftsmen. Also, it provides light and ventilation in the uninhabited attic. This is a double glazed window with standard glazing and has a uValue of 3.1. Application Our rooflights are designed for in such a way that you have the opportunity to bring light into uninhabitated spaces. It is not advisable to use this rooflight in habitable rooms because of their thermal performance. VELUX rooflights - GVT Frame and integrated flashing made of maintenance free polyurethane. Handle operated with three ventilation positions. Comes with an opening restrictor which engages at 90 only. Extruded aluminium sash which can be hinged on both sides, opening to an angle of 90. Sash can be opened on both sides at an angle of 90. Black internal and external finish. Properties  10 year guarantee on windows and flashings. Suitable for roof pitches between 20 and 65. *Not for use with standing seam metal roofs.