Pitched tile roof

The traditional sloped roof: clay tiles laid overlapping on battens, over a roof structure and an insulating, waterproof build-up. It is not a continuous membrane but a «scaled» covering: the pitch makes the water run off and the overlap between elements stops it creeping back up. Beneath the tiles, an underlay and an optional micro-ventilation collect and shed the water and moisture that get through.

The clay pitched roof is the discontinuous covering par excellence: many small units — Marseille, Portuguese tiles or pantiles — resting one on another to cover a sloping plane. It works by gravity and overlap, not by sealing; beneath, a modern build-up adds the insulation, watertightness and vapour control that the covering alone does not provide.

Each tile partly covers the one below: water slides from element to element down to the eaves without ever meeting an open joint toward the inside. For it to work, a minimum pitch is needed (different for each tile type) and a sufficient overlap: the lower the pitch, the longer the overlap must be, because the wind can drive the water up between the elements.

Beneath the tiles an underlay (breathable or waterproof membrane) is laid on boarding or directly on the battens: it collects the little water the wind drives under the covering, and the condensation, and channels it to the eaves. A counter-batten layer creates a micro-ventilation under the tiles, which dries the covering and, in summer, sheds part of the heat. Below sit the insulation and the vapour control layer.

The pitch can be carried by timber rafters and purlins with boarding, by a sloping clay-and-concrete floor or by a steel structure. The insulation can go between the rafters, over them (a «warm» roof with continuous insulation, no thermal bridges) or at the soffit. The position of insulation and vapour control must be studied so that the vapour rising from inside does not condense in the build-up.