- (415) 339-5810
Clay Tiles in Roofs Construction
The use of Terracotta for the production of tiles as roof material, dates back to ancient times; in this regard, we distinguish two basic types of roof tiles:
Barrel Tile – Also called coppo in Italian, cylindrical shaped, slightly tapered (conical section). It is the oldest form.
Flat Tile – Present in numerous geographical variants, according to if it was used as both cap and pan, or usually as pan to a barrel tile cap. In the latter case they are now known as “Roman Pans.”
Fire clay tiles have been used from the Mesopotamian civilization through the Greek, Etruscan-italic, Roman, and Byzantine one: an ancient history that unfolds, without interruption, through to today. It is during the Hellenistic period that the clay tiles evolve into a specialized building product, both from a technological/functional and aesthetical point of view.
It is interesting to note that in Greece – where there was a limited use of clay bricks, both raw and fired, because of the abundance of stones and marbles – there was an extensive use terracotta roof tiles. The need to protect and decorate the temples, made with more perishable materials (wood, mud-brick clay), lead Greek manufacturers to refine and adopt large-scale fire clay coatings.
The evolution of the gable roof with limited slope, with fronton and roof cladding in terracotta tiles, takes place in the Peloponnese, soon becoming the most popular feature for monumental buildings. It then spread out to all the colonized regions of Asia Minor, Sicily and Magna Graecia.
In the Hellenistic period two very different systems of terracotta roof cladding – both for the types of tiles and for the shape and color of the decoration – developed: the Spartan and the Corinthian roofs. The Corinthian one, more articulated and decorated, substituted the Spartan roof from the VI century B.C.
The Spartan roof basically consisted of barrel (semi-cylindrical) roof tiles overlapping each other as caps and pans alternatively. The Corinthian roof, more complicated, presents in its earliest stages a wide variety of forms: flat tiles with lateral curved margins or raised at a right angle (known today as Roman Pans because they became popular during the Roman period); and the barrel or triangulare tiles as caps. Sometimes these where made of a single piece (a Progenitor of the “S-tile”) we know today. Other special tiles that we still see today were created: for example the dedicated ridge tiles. The last elemnt of the roof would be antefixes – vertical blocks which terminate the covering tiles of a tiled roof, with a decorative and practical objective at the same time, adorning the building and stopping the birds from nesting inside the hole – conceived as a simple closure of the Roman Pan’s end, with a palmette in relief.
Recreation of a Greek temple’s Roof Cladding (G. A. Breymann, 1885)*
Greek colonies in western Sicily and Magna Graecia, developed a system of clay roof tiles that has traits of originality so we can actually identify a third type called Sicilian or Ionic. The characteristic feature of this system is represented by flat tiles combined with semi-cylindrical tiles. What most distinguished the Sicilian roof from the Spartan and Corinthian ones, however, is the absence of antefixes and the poverty of relief ornamentation.
Also in the Etruscan architecture, which preceded and for some centuries simultaneously developed with the Roman one, the use of terracotta elements for roof cladding had a long and important tradition.
The typical Etruscan roof is extremely decorated and colorful. The ridge of the roof is characterized by large tiles adorned with fantastic figures of wild beasts or deified ancestors; the gutter line is closed by the antefixes, often representing monstrous, comical and bizarre faces. The kinds of roof tiles used by the Etruscans are flat and barrel shaped and they overlap each other. We have also examples of Roman Pans adorned with a griffin head.
Recreation of an Etruscan temple, following the information of De Architectura by Vitruvio. (F. Bombardi, 1990)*
The clay roof cladding of the Etruscan temples, from the VI century B.C., shows influences from the Greek world in the shape of flat and semi-cylindrical tiles; the same thing happens with the antefixes female head-shaped.
The roof covering used by the Romans, followed straight from the Etruscan and Greek, in particular from the Sicilian model: the flat tiles overlap each other transversely in the direction of the slope of the roof. The barrel tiles are generally placed to cover the lateral connections of the tiles. Traingular caps dissapear in favour of the tapered barrel shape with one end wider than the other to help installation.
Example of Roman roof made of both barrel and flat tiles.
The Roman flat roof tiles have a pretty standard shape (rectangular or trapezoidal), while there are several variables regarding the size. Like the flat tiles, also Roman barrel tiles have few variations: predominantly barrel shape is now the preferred shape and the coice being straight or tapered edges to fit with the rectangular or trapezoid pans. Their typical reddish-brown color was due to a strong firing required to make such products, porous by nature, more waterproof.
The same technology developed by the Romans survived the fall of the West Empire, transmigrating into Europe and, in particular, in the Italy of the early Middle Ages. The monumental Roman public buildings, many of which have fallen into disuse, were seen as major deposits of stones, bricks, and roof tiles.
During late Middle Ages, there were attempts to standardize the brick production. Of all the craftsmen active in various fields of building production, furnaces workers were the most subject to regulation. Governments attempted to control the prices of bricks in order to protect the public’s interest in the area that covered the basic building material. It became essential to check the size of the bricks, as the furnace worker, when dealing with a selling fixed price, was tempted to cut costs by reducing the size of the product. So the second half of the thirteenth century onwards the municipal statutes of Venice, Padua, Pisa, Rome, Siena and other cities’ fixed the measurements for the bricks and bags of lime and regulated prices for each product type. Municipal statutes built models of bricks that were used as official unit of measurement. Sometimes the official model was accessible and permanently exposed in a public place. A city where you can still see on public display samples of bricks and tiles is, among others, Assisi. There is a reference sizes tool (“Abaco”) for the municipal measures for terracotta roof tiles and bricks at the base of the tower of Palazzo del Capitano del Popolo, with an inscription bearing the date of 1349.
Abaco for the municipal measures for terracotta roof tiles and bricks at the base of the tower of Palazzo del Capitano del Popolo, Assisi, Italy.*
A legend says that the typical curved barrel tile’s shape comes from the manufacturing, which used to take place on the top of the brick-maker’s thigh. Actually the tiles were “formed” – this is the exact term – in a mold of wood, prepared by a laborer. The shape was convex and had the edges on all 4 sides, edges that allowed manual compression of the mud clay, called marl. The lines on the back of the tile originated from the fingerprints of the brick-maker, who pressed the clay into shape for 600/700, even 800 times a day. After the press, the artifact was left to dry in the sun for at least one/two hours. Once the wooden molds were all used, the brick-maker used to peel the raw tiles and put them in a bed of sand to make them dry. After 20/30 days of drying they were placed in the kiln and fired for several days.
In order to allow an efficient flow of rainwater, the use of the tiles had to be necessarily associated with the construction of pitched roofs; it means that tiles have been the exclusive roofing system until the advent of reinforced concrete (early 1900), which has allowed the construction of flat roofs, waterproofed by application of tarred paper. The use of tiles remains extremely popular for aesthetic reasons, preservation of scenic and historical heritage, and also for the efficiency of the material in terms of thermal and hydro insulation.
Roman Roof Tops: patching up roofs is an organic, ongoing process.
Given the extreme diversity of geographical contexts in which the tiles were used in Europe, it was inevitable that they would have evolved to various shapes and sizes.
The tile can also vary depending on its position on the roof (for example, those on the ridge are larger than those on the sloping areas). The color of the tiles is another important variable: it changes according to the different geographical regions because different clay produces different color tiles, but also different firing times and temperatures affect the final color.
This is still the most common type of roofing throughout Mediterranean countries and it is still considered very affordable.
The features that characterize terracotta roof tiles and make them the most popular choice are:
- Excellent resistance to water and frost.
- Exceptional thermal insulation by reducing unwanted heat loss or gain and decreasing the energy demands of heating and cooling system.
- Longevity, a lifetime measured in centuries.
- Porosity, which allows vapors formed underneath the roof to be absorbed and then evaporated on the outside.
- Architectural versatility.
In Europe there are numerous clay roof tiles production centers that use both traditional techniques and innovative materials and designs.
It is important to say that it is becoming more and more popular in the construction and architecture industry to reclaim, resell and reuse old tiles, which have a unique and amazing allure due to time, wear and character.
Eternal Roman Roof Tops
* Pictures from Tetti in Laterizio by Alfonso Acocella, Laterconsult Pubblisher, Roma, 1994