A device for fixing an item to a building structure, for example for use as a roof fixing, is disclosed. It consists of a base plate (30) having a projecting member projecting from one side of it, for example a threaded stud or bolt (40), and an impermeable cover member, for example in the form of a solid block (35) which can be threaded on to the projecting member. The cover member compresses a waterproof membrane located between it and the base plate (30) to form a waterproof seal. The waterproof membrane extends past the edges of the base plate (30) and its projecting edges are sealed to the structure.