Abstract: A skylight system is provided for installation on a roof in such a manner to remain weather-tight over a wide range of temperatures. Transparent or translucent panels in aluminum frames are mounted to a steel roof of a building by suitable connectors. Upon a change in temperature, the aluminum frame will expand or contract at a rate different from that of the steel roof, causing relative displacement between the skylight and the roof. To allow for a weather-proof seal to be maintained between the skylight and the roof, a slip joint is provided by means of an aluminum flange fixed to the skylight frame and having an inwardly extending lip spaced above and parallel to the outer face of the skylight and a steel flashing having a U-shaped bend along its free edge slipped over the lip of the flange and at its opposite edge being attached to the roof.