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.
Translucent sheets should be fastened in the same way as metal cladding, except that extra or special fixings are required because plastic sheeting deflects more.
A different depth or screw gun torque setting may be required to avoid over tightening and subsequent distortion around the fixing. Because of their different rates of thermal expansion, plastic and metal sheet fixings should be fastened through oversized holes. Support for plastic sheeting is obtained from the metal sheeting for downward loads and span-breakers for uplift loads. See 14.8.4 Midspan Supports.
Side laps must be fixed at a maximum of 600 mm centres (fixing details in 14.8.1 Side-Lap Fixing) and are required to be sealed where the roof pitch is less than 10° and in high wind design load areas.
Oversized holes and load-spreading washers must be used when fixing roof lights to metal sheeting. All plastic roof lighting must have pre-drilled intermediate side lap fastenings with oversized holes on all spans larger than 1.2 m. See 14.8.1 Side-Lap Fixing
To avoid stress, roof lights should always be fixed starting from one end and fixing the intermediate purlins before doing the ends.
Deflection limits should be placed on the performance of plastic sheeting to ensure longevity and to avoid incremental failure due to flexing at the fixing points. This can be done by using mid-span supports. Plastic sheeting should not be used in applications where it approaches its deflection limits (50 mm).
The two main factors that limit spanning capability are deflection and pull-through over the fasteners.
As standard weight plastic roof lights have a low pull-over load and the critical condition is that imposed by wind suction; their performance is determined by the number of fasteners per square metre.
All fixings and washers must meet the same durability standard as the roof and wall cladding.
All plastic sheeting must have an enlarged fixing hole for the provision of thermal movement, predrilled to the following diameters for 12# or 14# self-drilling screws for both timber and steel purlins.
The fixing must be positioned in the centre of the oversize hole to ensure that the sheet has equal movement in all directions around the fixing.
Sheets up to 6 m
Sheets 6 to 9 m
Sheets 9 to 18 m
|For PVC and Polycarbonate|
Sheets up to 4 m
Sheets up to 6 m
Sheets over 6 m
In extreme environments where there are chemical fumes and the fixings are prone to chemical attack from the inside of a building, stainless steel fixings should be used.
When pan fixing is used, the fastener should be positioned within 25 mm of the rib.