Roof tiles

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 or nails, but in some cases historic designs utilize interlocking systems that are self-supporting. Tiles typically cover an underlayment system, which seals 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 shingles overlapping it. As a result of this, flat tiles 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 Greeks, Romans, and Chinese. 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

s 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 in some cases be produced through a variety of methods, interlocking tiles can only be manufactured on a large scale 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 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

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' 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.

Northern Europe

It is believed that the Romans introduced the use of clay roof tile to Britain after their conquest in AD 43. The earliest known sites for the production of roof tile are near the Fishbourne Roman Palace. Early tiles produced in Britain followed the Roman imbrex and tebula style, but also included flat shingle tiles, which could be produced with less experience.
For a while after the dissolution of the Roman Empire, the manufacture of tile for roofs and decoration diminished in Northern Europe. In the twelfth century clay, slate, and stone roofing tile began to see more use, initially on abbeys and royal palaces. Their use was later encouraged within Medieval towns as a means of preventing the spread of fire. Simple flat shingle tiles became common during this period due to their ease of manufacture.
Scandinavian roof tiles have been seen on structures dating to the 1500s when city rulers in Holland required the use of fireproof materials. At the time, most houses were made of wood and had thatch roofing, which would often cause fires to spread quickly. To satisfy demand, many small roof-tile makers began to produce roof tiles by hand. The Scandinavian style of roof tile is a variation on the pantile which features a subdued "S" shape reminiscent of an ocean wave.
In Britain, tiles were also used to provide weather protection to the sides of timber frame buildings, a practice known as tile hanging. Another form of this is the so-called mathematical tile, which was hung on laths, nailed and then grouted. This form of tiling gives an imitation of brickwork and was developed to give the appearance of brick, but avoided the brick taxes of the 18th century.

Asia

China

Clay roof tiles are the main form of historic ceramic tilework in China, due largely to the emphasis that traditional Chinese architecture places on a roof as opposed to a wall.
Roof tile fragments have been found in the Loess Plateau dating to the Longshan period, showing some of the earliest pan and cover designs found in Asia. During the Song dynasty, the manufacture of glazed tiles was standardized in Li Jie's Yingzao Fashi. In the Ming dynasty and Qing dynasty, glazed tiles became ever more popular for top-tier buildings, including palace halls in the Forbidden City and ceremonial temples such as the Heavenly Temple.
Chinese architecture is notable for its advancement of colored gloss glazes for roof tiles. Marco Polo made note of these on his travels to China, writing:

The roof is all ablaze with scarlet and green and blue and yellow and all the colors that are, so brilliantly varnished that it glitters like crystal and the color of it can be seen from far away.

Japan

includes Onigawara as roof ornamentation in conjunction with tiled roofs. They are generally roof tiles or statues depicting a Japanese ogre or a fearsome beast. Prior to the Heian period, similar ornaments with floral and plant designs "hanagawara" preceded the onigawara.
Onigawara are most often found in Buddhist temples. In some cases the ogre's face may be missing.

Korea

In Korea the use of tile, known as giwa, dates back to the Three Kingdoms period, but it was not until the Unified Silla period that tile roofing became widely used. Tiles were initially reserved for temples and royal buildings as a status symbol.
The designs used on giwa can have symbolic meanings, with different figures representing concepts such as spirituality, longevity, happiness, and enlightenment. The five elements of fire, water, wood, metal and earth were common decorations during the Three Kingdoms period, and during the Goryeo dynasty Celadon glaze was invented and used for the roof tiles of the upper class.
Many post-war Korean roofs feature giwa and a common ornamental symbol is the Mugunghwa, South Korea's national flower.