Roof tiles are overlapping tiles designed mainly to keep out precipitation such as rain or snow, and are traditionally made from locally available materials such as clay or slate. Later tiles have been made from materials such as concrete, glass, and plastic. Roof tiles can be affixed by screws, nails, wire clips, or self-supporting lugs and interlocking designs. In desert or tropical climates tiles are sometimes installed directly on laths and battens, but in temperate climates tiles are typically installed atop an underlayment system to protect the roof against water intrusion.
Categories There are numerous profiles, or patterns, of roof tile which can be separated into categories based on their installation and design.
Shingle / flat tiles
One of the simplest designs of roof tile, these are simple overlapping slabs installed in the same manner as traditional shingles, usually held in place by nails or screws at their top. All forms of slate tile fall into this category. When installed, most of an individual shingle's surface area will be covered by the tiles overlapping it, with a minimum of two tiles overlapping at any one point. As a result, shingles require more tiles to cover a certain area than other patterns of similar size. These tiles commonly feature a squared base, as is the case with English clay tiles, but in some cases can have a pointed or rounded end, as seen with the beaver-tail tile common in Southern Germany.
Imbrex and tegula
The imbrex and tegula are overlapping tiles that were used by many ancient cultures, including the Chinese, Greeks, and Romans. The tegula is a flat tile laid against the surface of the roof, while the imbrex is a semi-cylindrical tile laid over the joints between tegulae. In early designs tegula were perfectly flat, however over time they were designed to have ridges along their edges to channel water away from the gaps between tiles.
Mission / Monk and Nun tiles
Similar to the imbrex and tegula design of tile, mission tiles are a semi-cylindrical two-piece tile system, composed of a pan and cover. Unlike the imbrex and tegula both the pan and cover of Mission tile are arched. Early examples of this profile were created by bending a piece of clay over a worker's thigh, which resulted in the semi-circular curve. This could add a taper to one end of the tile.
Pantiles / S tiles
Pantiles are similar to mission tiles except that they consolidate the pan and cover into a single piece. This allows for greater surface area coverage with fewer tiles, and fewer cracks that could lead to leakage. These tiles are traditionally formed through an extruder. In addition to the S-shaped Spanish tiles, this category includes the Scandia tiles common to Scandinavia and Northern Europe.
Interlocking tiles
Dating to the 1840s, interlocking tiles are the newest category of roofing tile and one of the widest ranging in appearance. Their distinguishing feature is the presence of a ridge for interlocking with one another. This allows them to provide a high ratio of roof area to number of tiles used. Many distinct profiles fall into this category, such as the Marseilles, Ludowici, and Conosera patterns. Unlike other types of tiles, which can often be produced through hand-forming methods, interlocking tiles can only be manufactured with a tile press. In many cases interlocking tile is designed to imitate other patterns of tile, such as flat shingles or pantiles, which can make it difficult to identify from the ground without inspecting an individual tile for a ridge.
History as a vernacular material The exact origins of clay roofing tiles are obscure, but it is believed that it was developed independently during the late Neolithic period in both ancient Greece and China, before spreading in use across Europe and Asia.
Europe
Greece It is believed that clay roof tiles were first used in Ancient Greece between 2000-3000 BCE. Fired roof-tiles have been found in the House of the tiles in Lerna, Greece. Debris found at the site contained thousands of terracotta tiles which had fallen from the roof. In the Mycenaean period, roof tiles are documented for Gla and Midea. The earliest roof tiles from the Archaic period in Greece are documented from a very restricted area around Corinth, where fired tiles began to replace thatched roofs at two temples of Apollo and Poseidon between 700 and 650 BC. Spreading rapidly, roof tiles were found within fifty years at many sites around the Eastern Mediterranean, including Mainland Greece, Western Asia Minor, and Southern and Central Italy. Early Greek roof-tiles were of the imbrex and tegula style. While more expensive and labour-intensive to produce than thatch, their introduction has been explained by their greatly enhanced fire-resistance which gave desired protection to the costly temples. The spread of the roof-tile technique has to be viewed in connection with the simultaneous rise of monumental architecture in Ancient Greece. Only the newly appearing stone walls, which were replacing the earlier mudbrick and wood walls, were strong enough to support the weight of a tiled roof. As a side-effect, it has been assumed that the new stone and tile construction also ushered in the end of 'Chinese roof' (Knickdach) construction in Greek architecture, as they made the need for an extended roof as rain protection for the mudbrick walls obsolete. A Greek roof tile was responsible for the death of Molossian Greek king Pyrrhus of Epirus in 272 BC after a woman threw one at the king's head as he was attacking her son.
Roman Empire Roof tiles similar to Greek designs continued to be used through the reign of the Roman Empire. They were a common feature in Roman cities, despite the fact that a single tile would often cost the equivalent of 1.5 day's wages. Tiles were commonly used as improvised weapons during citizen uprisings, as they were one of few such weapons available to city-dwellers of the time. Roman imbrex and tebula roofs generally avoided the use of nails and were instead held in place through gravity, it is possible that this was one of the reasons their tile was found on low pitched roofs. The Romans spread the use and production of roofing tile across their colonies in Europe, with kilns and tile-works constructed as far west and north as Spain and Britain. Early records suggest that brick and tile-works were considered under the control of the Roman state for a period of time.
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