In planing the size of window, the optimum daylight level relative to the purpose of room must be the deciding factor. For instance, building regulations require a minimum window area of 1/8 of the floor surface area for living rooms.
Large windows make living rooms more comfortable. The window width in secondary rooms can be chosen according to the distance between the rafter. Generously wide windows in living rooms can be achieved by the inclusion of rafter trimmers. Steeper roofs need shorter windows, while flatter roofs require longer windows. Roof window can be joined using purpose – made prefabricated flashing, and can be arranged in rows or in combinations next to or above one another.