Part 1: Architect’s Guide 1 - 39 5.2.4 Steep or arched roofs Water tightness is easily obtained by overlapping of the metal sheets, more or less following the roof slope and the product. The most common procedure is to superimpose materials so that all air space is eliminated. Figure 5.14 Curved roof 5.2.5 Roof construction A typical roof construction, from the exterior inwards, consists of: A ribbed steel decking fixed perpendicular to the panels A primary layer of insulation made of a taut felt sheet combined with an internal vapour screen placed between the decking and panels A second and thicker layer of mineral wool A steel frame on which to fix the product which is used for the internal finish A second vapour screen An internal finish facing material, of one or two layers of plasterboard screwed to the steel frame or, in some cases, steel decking or perforated steel decking. Acoustic insulation to control rain noise is particularly effective. Roof netting systems with different amounts of perforation can be fixed on metal roofs to handle thermal shock and to improve the architectural concept using a canopy. Galvanized steel sheets, whether pre-painted or not, and stainless sheets, are particularly suitable for arched roofs (see Figure 5.15). Stiffening ribs improve bending strength. The plates are supported by panels, the characteristics of which determine the spacing and loads to be carried. Fixing is carried out above the stiffening ribs, using compressed watertight joints.
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