Crest Fixing

Crest fixing is the most common type of fastening of roof cladding in New Zealand.

For fixing into timber a Type 17 self-drilling fastener that has a pierce point slot thread is used, which penetrates the roofing metal and then threads itself into timber.

The embedment into soft wood must be a minimum of 30 mm and greater than 6 times the screw thread diameter.

For fixing into steel, a self-drilling fastener with a drill point of a diameter suitable for the tapping size of the fastener is used. Extended drill points are available for drilling up to 12 mm thick steel and the pitch spacing of threads should be increased as the steel thickness decreases. See Self-Drilling Screws.

Steel embedment should be 5 to 6 mm beyond the drill point with a minimum of 3 threads beyond the drill point.

Screws are specified by gauge, TPI (threads per inch), and length.

Self-threading screws require a pre-drilled hole in the cladding and structure. The tapping size drill diameter is determined by the TPI and gauge of the fastener.

Both self-drilling and self-tapping screws can have different points, TPI, and heads to suit the particular requirements of the connection.