Metal panel roofs, and load support structures for supporting loads on such roofs. Side rails provide primary support for loads on such roofs. The side rails can be fabricated from sheet metal or can be extruded. A side rail includes a standing seam cavity which is lowered, and covers, the standing seam. Side walls of the standing seam cavity. An upstanding web extends up from the cavity, and lower shoulders may extend laterally, optionally downwardly, from the walls which define the cavity, on either one side, or both sides, of the cavity. Building roof insulation can extend up through an aperture in the roof, surrounded by such load support structure, and extend up to the top of the side rail, thus providing a thermal break between the load support structure elements and the space surrounded by the load support structure.