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.
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.
The COP recommends using screws rather than driven fasteners, in all cases.
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:
Profiled washers should have an EPDM sealing washer.
| Gauge | Diameters Nominal |
|---|---|
| Shank | |
| mm | |
| 6 | 2.5 |
| 8 | 3 |
| 10 | 3.5 |
| 12 | 4.1 |
| 14 | 4.8 |
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.
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.
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.
