Our fixed curb mount GS model is designed to be used on a site-built curb. Curb mounted skylights consist of an insulated glass sealed between a thermally efficient ,maintenance free, vinyl curb frame and an aluminum outer retainer frame. Wasco flashing (shingle and tile roofs only) is installed around the site-built curb. The skylight is then mounted onto the flashed curb and fastened into place. Outside Curb Dimension: 25-1/2" X 49-1/2". Daylight Area: 21-1/8" X 45-1/8". Daylight Area (Sq. Ft.): 6.61.