Primary Fasteners

Primary fasteners are those that attach roof or wall cladding to the building frame. Because they are relied on for structural performance, they should be capable of withstanding the design withdrawal load specific to the site and their location on the building. They should be able to withstand all loads applied to the sheeting, including those due to expansion, and remain watertight.

Fasteners should not be overdriven as that can damage the sealing washer, distort the roof cladding, and cause leaks. Screw fasteners should not be overdriven as this can affect the pullout values and cause strip-out when fastening to light gauge purlins or battens.

The shank diameter and thread type of the fastener will determine the withdrawal loads into either timber or steel, so the designer or contractor should ensure that the fastener complies with the requirements of Fastener Performance.

The number of fasteners per square metre required to resist all wind or other loads on a building depends on the type of fastening.

Primary fasteners for timber consist of nails and screws with varying diameters , but their performance should be individually assessed.

When using light gauge metal roof and wall cladding the size of the head will determine the performance of the sheeting under load, as the calculation of pull-over strength assume that either the screw or the nail washer has a minimum head size of 12 mm. See Pull-over Values.

Fasteners with heads smaller than 12 mm, such as wafer heads and proprietary screws for fixing miniature profiles used without metal or sealing washers, should not be regarded as a substitute for primary fixings for metal claddings. These fixings can be used with different fastening patterns to those in Fastener Patterns, but the pull-over load should be determined from tests and should not be confused with the pull-out values provided by the manufacturer.

The fastener to connect battens or purlins to the structure is a primary fastener, and if the roofing contractor is responsible for attaching these members, the wind uplift load should be determined. See Wind Load and Purlin-Rafter Connections.