Solar roof tile mounting adaptor

An adaptor 20 for mounting a solar thermal collector system on a pitched roof. The adaptor 20 enables the solar thermal collector, or assembly of collectors, to be interlocked with surrounding rows of roof tiles or slates in such a way as to maintain the inherently weather-tight overlapping structure, whilst maintaining the solar collectors flush with the roof surface. The adaptor 20 has an "overlapping" flange 22 along one side edge, and an "underlapping" flange 24 along the opposite side edge to allow the adaptor to mate with either a right hand or left hand end of a solar collector assembly. The adaptor 20 comprises a depression 26 for receiving downwardly dependent edges of part-cylindrical or part-conical tiles. The adaptor 20 can include a toothed flange 34, 42 to allow water drainage and to prevent animals from nesting under the adaptor 20 when installed.