For a period of time the tile industry allowed a reduced fastening pattern in an effort to complete against asphalt shingles, which offered an impressive look and has an increased useful life. During this time many roofs were installed with very few fasteners. One manufacturer’s specifications required one nail every fifth (5th) row at each third (3rd) tile. Some roofers still use the old method citing the tile’s weight as sufficient down-force. Today’s code requires screws, not nails. Specially bonded mortar and tile adhesive polyurethane are also approved fastening methods. Unfastened tiles are prone to movement and slipping.