COP v3.0:installation; fasteners

14.13 Fasteners 

The durability of fasteners should equal or exceed that of the material being fastened, and the fastener metal or coating must be compatible with the cladding material if in contact. Fasteners used pre-painted steel products should be factory colour matched before installation.

14.13.1 Nails 

The traditional New Zealand roof fastener was until 1980 the "Lead Head", a flat-headed smooth shank steel nail with a lead head cast on it. Lead heads often 'backed out' causing leaks, the shanks were prone to corrosion, and lead is incompatible with modern metallic coatings.
Spiral Shank nail fasteners have a galvanised shank, and the spiral shank has over twice the withdrawal resistance of a smooth shanked nail. They are however still prone to backing out, and the under-head seal is not as robust as the neoprene seals used on modern roofing screws.

The COP recommends using screws rather than driven fasteners, in all cases.


14.13.1A Nail Pull-out

Driven Fasteners can back out over time.


14.13.2 Screws 

Screw fasteners should be long enough to give adequate penetration into the supporting structure. Generally, 30 mm embedment is required for screws into timber or three threads engagement for screws into steel. Refer to roofing manufacturers for specific recommendations.

Fasteners should be:

  • a minimum of Class 4 for Severe Environments,
  • Class 5 for Very Severe Environments,
  • manufactured and coated with materials compatible with the material being fastened, and
  • fitted with low carbon, non-conducting sealing washers.

Profiled washers should have an EPDM sealing washer.


14.13.2C Screw Thread Types


Screw fasteners are identified by their length, gauge pitch (threads per inch) and their drill point. The drill point may be type 17 for driving into timber or drill point for driving into steel. Reduced diameter drill points, which can be used for either function, are also available.

14.13.3 Clip Fasteners 

Secret-fixed roofs will be attached to the primary structure by a proprietary clip that is screwed or nailed to the purlins. These profiles offer the advantages of fewer penetrations through the cladding, and thermal expansion is unimpeded.

Clip and bracket fasteners can be purpose made to provide the same attributes to most flashings.

14.13.4 Rivets 

Rivets should have a minimum diameter of 4 mm.

Use aluminium rivets for galvanised sheets and aluminium/zinc-coated steel products; monel rivets are incompatible with aluminium and zinc products.

Sealed rivets are preferred over unsealed rivets, as they do not require adding sealant on the face to achieve weatherproofing.


14.13.4A Rivet Setting

Blind rivets are placed through a pre-drilled hole then are set by rivet tool withdrawing the mandrel. This expands the rivet pin, clamping the material between the rivet pin and the rivet head. The pin eventually snaps free.