Fakro Flat Roof Window Fixed Dome & Kerb - 800mm x 800mm Please note this is a anti-burglary double glazed unit with a single polycarbonate dome. This is a fixed, non-opening dome & kerb. Dimensions Dome size: 800mm x 800mm. Minimum roof opening: 800mm x 800mm. Maximum roof opening: 850mm x 850mm. uValue: 1.2W/mk. Upstand: 150mm. Description A specially profiled covering materials under the drip cap of the frame facilitates the finishing of the window connecting with the roofing material. The flat roof window can be also mounted on an additional base with a height of 15cm, which raises the window and allows it's installation eg. in green or living roofs.