Abstract: The method includes providing a rigid mould (8, 150) with at a re-entrant cavity (96, 196). Mouldable material is provided on the rigid mould and the re-entrant cavity is filled to form a hook-like protuberance (36) on a surface of the moulded building product to facilitate, in use, the attachment of the building product to the structure of a building. The mouldable material sets to form a building product. The building product is removed from the mould. The re-entrant cavity has a resilient portion to facilitate the removal of the building product without detrimental affect to the hook-like protuberance. The so-formed building products have a greater resistance to inclement weather conditions. The building product may be a concrete roof tile formed by a roller and slipper extrusion method, a clay tile made by pressing in a clay tile press, or a cast concrete roof tile.

Abstract: The invention concerns a novel roof system comprising a plurality of roof insulation panels (4) moulded from foamed polystyrene or the like material, the panels being mounted on a roof structure, which may comprise conventional purlins and rafters with roof battens or a closed roof decking of timber or the like material. In either case, the panels are supported by the roof structure and in turn provide location and support for a plurality of roof tiles (6, 6a). In order to enhance the location and support of the roof tiles on the panels, the panels are provided with upstanding walls having re-entrant angled surfaces (32) for engagement by hook-like protuberances (60a, 60b, 61a, 61b) provided towards lower ends, in use, of the roof tiles. The roof tiles may be made from cementitious compositions, ceramic compositions or reconstituted slate materials. The roof system may also include reinforcement for the panels, which may be provided with for mutual interlocking engagement with sideways adjacent panels in use.