Types of fixing

Primary fixings attaching metal cladding to steel rails are commonly self-tapping screws (Fig. 5.24).

Blind light rivets are usually used for secondary fixings in metal claddings. For steel sheeting, cadmium-plated Monel metal rivets should be used, not cadmium-plated mild steel. Rivets in aluminium sheeting should be aluminium alloy (Fig. 5.25).

Cartridge-assisted fasteners, as shown in Fig. 5.26, are used to secure metal roof deck units, but are not used where watertightness relies upon careful tightening against a washer seal, such as is required when fixing roof and wall cladding sheets. Welded or screwed stud fixings for impaled sheets should not be used for metal sheet cladding.

For the aluminium roof sheeting at Stansted Airport the sheeting was fixed to the supporting steelwork on the ground. Because of the improved


5.22 Fixing positions using steel or aluminium sheets: (a) crown fixings for sinusoidal sheeting; (b) trough fixings for trapezoidal sheeting.

5.23 Examples of side-lap joints with secret fixings: (a) fixings without accessory section; (b) fixing with accessory section.

quality control available with visual inspection at ground level, fixing through the trough of profiles was possible (Fig. 5.27).

Sheet cladding may fail at the fixings, either by pull-through or by failure of the fixing itself. Fixing should therefore be specified to include nuts, washers and weather-seal devices, all preferably from the same manufacturer

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