Abstract: The invention provides a number of embodiments of slidable brackets adapted for mounting building panels, especially roof members mounted to structural members in a manner to permit limited uni-axial or bi-axial movement. A preferred embodiment has a channel shaped base member and a channel shaped slider member. The base member is adapted to be secured to an existing roof or to a building frame component. The slider member is formed to slidingly straddle and slide on the base member. For uni-axial motion, the slider member has a single pair of longitudinal slots formed in each of its sides through which a bolt or the like passes and which also passes through a mating bolt hole in the side of the base member. For bi-axial motion, a pair of slots is formed in an attached beam whose axis extends in a direction perpendicular to the axis of the longitudinal slots in the slider member.