The coppo, or curved tile, locally also called "channel", traditionally produced by molding and industrially by extrusion, has roughly the shape of a third of a truncated cone (at first sight it looks like a portion of a cylindrical surface, because the taper is just perceptible). The typical dimensions, which vary in the various regional traditions (Venetian tile, Piedmontese tile, etc.) are 45-50 cm long and 13-20 cm wide.
The requirement per square meter of coverage is quite variable due to the very flexible overlap measure. However, about 28-30 tiles are required, to be arranged below in convex rows (channels) and above in concave rows (covered), with overlaps of approximately 6 cm; the result is a weight per square meter of about 60-66 kg. The slope of the water table is generally not less than 30%.
It was already widely used by the ancient Romans, but also known by Greeks and Etruscans. Its diffusion in historical times included southern Europe and the whole Mediterranean, including the Arab world.
It represents the most widespread type of coverage in Italy. It has the drawback of tending to slide downwards over time; to ensure stability of position, versions are on the market equipped with simple systems that allow one tile to be anchored together with the other.