Manufacturers will sometimes use lighter gauge material as it is more cost-effective, but this has significant implications for the design of the building envelope. Lighter gauge material will have a greater deflection for a given load, resulting in reduced spanning or load carrying ability. It is also more likely to fail due to web buckling, particularly if used in double or multi-span conditions.


The normally specified gauges for roof and wall cladding are 0.7mm and 0.5mm respectively. These gauges are the result of structural calculations and a record of in-service performance. Using lighter gauges may achieve some short term costs savings, but it will usually lead to a poorer performing building and increased costs in the future.


Profiled metal cladding


Pre-finished steel is usually roll formed to create a profile which is both functional and aesthetic.


Profiles are often referred to generically, for example a 32/1000 profile. This defines the depth of the profile as 32mm and the cover width of the sheet as 1000mm.


However this does not define the full geometry of the sheet as it does not specify the number or exact shape of the profiles.


Each profile can be defined by a number of parameters which are shown in the diagram below. Altering these parameters and the gauge of material will affect the structural performance of the cladding.


Figure 2. A typical trapezoidal profile indicating common nomenclature G F E D C B


A B C D E F G


Depth Crown Valley Pitch Rib Trough Web


A


The load capacities calculated to BS 5950-6: 1995 are only valid if the profiles have been manufactured to the tolerances specified in BS 5950-7: 1992 using material that has been produced to the appropriate British and European Standards. Specifiers should ensure that this is the case by specifying systems that have been assessed by Tata Steel, SCI or an independent accreditation body.


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