Most Common Roofing Materials
A lot of materials are used to build roofs. Romans and Greeks made them with tiles carved in stone materials in representative buildings and with pottery tiles in the others. The Arabs normalised the so-called Arabic pottery tile, which solved all the problems of an inclined roof with a single piece, always the same one very similar to the Roman blanket: channels, blankets, limatesas and limahoyas.
The flat roofs were also made with ceramic pieces in the form of tiles, on constructive dispositions that resolved the problem of expansion without affecting the construction they protect. In countries with a particularly dry climate, uncooked clay was used (and continues to be used) directly to finish off the roofs.
In poorer areas, flat pieces of stone, mainly slate, were used as roofing tiles. Flat roofs have the serious disadvantage that, as water can slip through capillarity between the pieces, steep slopes of more than 50% are required and large overlaps between them in order to avoid this; therefore the unit weight (per unit area) of the roof is usually very large. On the other hand it is a material that resists well the weather (frosts) and of great durability.
On flat roofs, the upper part was protected over the various waterproofing layers by means of pottery tiles (known in Spain as Ariza tiles or, smaller and thinner, Catalan tiles).
A very convenient arrangement for flat roofs consists of the so-called inverted roof: if it is normal to put the thermal insulation under the roofing material (hence the name inverted), it rests directly on the top panel and the waterproofing, and on top of it a protective layer, which may be large-size tiles or a layer of river boulder. Thermal insulation (made of a water-repellent material such as expanded polystyrene) protects the waterproofing layer from the sun’s rays and excessive cold (preventing it from freezing) while avoiding movements due to expansion due to changes in extreme temperatures (the roof undergoes the most important changes). Rainwater slides under the insulation and is drained.
Today there are also green roofs, made from different types of plants that are even used in facades.