Abstract: A system for mechanically attaching a flexible waterproof membrane to an underlying roof structure including an elongated fastening bar which is placed above the membrane and fastened to the roofing structure with fasteners, such as screws or nails, which are driven through the bar from the top thereof through the underlying membrane and into the roof structure, and an elongated waterproof strip having (a) a central region sandwiched beneath the bottom of the bar and the membrane, and through which the fastening screws or nails also pass, and (b) marginal regions which wrap upwardly around the bar and overlap each other above the bar and the heads of the fasteners, providing a waterproof seal for the bar with a double thickness layer of strip material above the fastener heads.