The 2014 revision of BS 5534 the Code of Practice for Slating and Tiling, highlighted mortar as being an insufficient means of securing tiles to the roof. In particular this applies to the fixing of ridge and hip tiles, which was identified by the National House Building Council (NHBC) as the number one cause of roof failures that resulted in claims.
To this end, BS 5534 now states that even if mortar is used, then the ridge and hip tiles must also be mechanically secured to the roof.