Clay Roof Tile

A clay roof tile is a unit of shaped clay that has been dried and fired in a kiln, then laid in overlapping rows on a pitched roof. Clay tiles have been made for nearly three thousand years and remain the predominant roof covering in much of southern Europe, Latin America, North Africa, the Middle East and parts of Asia. Where good clay is plentiful, tile production has often been tied to local brickworks.

History

Fired roof tiles appear to have developed independently in late Neolithic Greece and in China. Some of the earliest securely dated examples come from temples near Corinth, around 700-650 BC. The Greek and Roman system used flat tegulae with half-round imbrices over the joints, and Roman builders carried tile-making across their empire, including Britain after AD 43. In China the Song-dynasty building manual Yingzao Fashi standardised glazed tile manufacture. Mass-produced interlocking tiles appeared in France in the 1840s, and later spread worldwide, including through factories such as those at Mangalore in India.

Main families

• Flat or plain tiles: small overlapping slabs hung or nailed at the head, laid double-lap like slates; includes the German beaver-tail (Biberschwanz).
• Two-piece curved tiles: pan and cover, as in the Roman imbrex and tegula and the mission or "monk and nun" tile.
• One-piece curved tiles: the pantile and the Spanish S-tile, which combine pan and cover.
• Interlocking tiles: pressed tiles with side and head grooves, such as the French or Marseille tile.

Properties

• Durability: high-quality clay tiles have a proven life of more than 100 years.
• Absorption: depends on the clay and firing; some manufacturers achieve under 2% moisture absorption. Tiles for frost-prone regions must be fired close to vitrification.
• Colour: comes from the clay itself (iron oxides give the familiar red) or from an engobe or glaze. Unlike concrete, fired colour does not fade significantly.
• Strength: breaking loads for higher-grade tiles are reported in the range of about 700-1,500 lbf (3.1-6.7 kN).
• Weight: clay tile is heavy compared with shingles, so roof framing must be designed for it.

Regional notes

In the United States, clay tile is most common in the South, Southwest and Florida, where it is valued for longevity and performance in hurricanes when properly fastened. Mission-style clay tile was first produced in California in 1780. On Java, about 90% of houses use clay tile. In the US and Canada, installation guidance is published by the Tile Roofing Industry Alliance, based in Seattle.

Maintenance

Clay tiles themselves rarely wear out; problems usually arise from broken tiles, failed underlayment, corroded fixings or deteriorated mortar at ridges and hips. Walking on tiles can crack them, so repairers use roof ladders or step only on the strongest points.