The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
Secondary fasteners are used to attach cladding sheets to one another, to transfer loads and to provide side lap sealing. They should be used in conjunction with primary fasteners to comply with the site wind design load. Because side and end laps are subject to shear loading caused by expansion and differential movement, the wind load and point load requirements will not be met unless secondary fasteners are used.
Laps on purlin spacings over 1.2 m should be stitched at mid-span with coarse thread stitching screws or self-sealing 4.8 mm aluminium blind rivets. This applies when fixing self-supporting ribbed metal profiled cladding, but not self-locking profiles.