Both steel and aluminium offer a wide variety of sharper (trapezoidal) profiles, and can be used horizontally or vertically with patent bending processes available for specially formed corner junctions. The use of horizontal metal sheeting at the IBM offices at Greenford (Fig. 5.14) (architects: Foster Associates), for example, encouraged other architects to use profiled metal sheeting in a similar manner The selection of
either steel or aluminium may be a personal choice. Aluminium is nominally more expensive but, on the other hand, is lighter and therefore, in theory, needs less framing. In practice, because the actual difference is 1.5 kg/m2, this makes no difference to the framing in most cases. Maybe the specifier is influenced by steel being, in theory, more susceptible to rusting at the edges of the sheets. In truth, the choice probably rests on the types of finishes available or even the standard of technical back-up service provided by the manufacturers.
5.15 Tapering close-profile flashings available in aluminium.
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