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.
For sprung curved roofs, the purlin/rafter connection must be increased at the eaves.
Long lengths of pierce fixed roofing will impose added loads to the purlin connection due to thermal movement of the roof.
3.14.1A Purlin to rafter fastener requirements for SG8 Radiata pine in accordance with NZS 3604:2011
|Use 70 x 45 mm radiata pine on flat minimum|
|Use 90 x 45 mm radiata pine on flat minimum|
|Rafter Spacing||Purlin Spacing||Low Wind Zone||Medium Wind Zone||High Wind Zone||Very High Wind Zone||Extra High Wind Zone|
|Type||Fastener||Fixing Capacity (kN)|
|A||1/90 x 3.15 gun nails||0.55|
|B||2/90 x 3.15 gun nails||0.80|
|C||1/10g x 80 mm self-drilling screw||2.40|
|D||2.10g x 80 mm self-drlling screws||3.45|
|E||1/14 g X 100 mm self-driling screws||5.50|
The maximum overhang for all corrugate and low trapezoidal profiles is 150 mm, unless a product has been specifically tested to withstand point load and design wind loads at a greater overhang.
The allowable overhang distance of various cladding profiles will depend on their section properties.
The limit placed on low trapezoidal profiles with a stiffened overhang is 300 mm but it is not suitable for corrugate.
The overhang distance can be increased for some trapezoidal profiles with a rib height greater than 28 mm, but this distance must be proved by testing.
Where the cladding is fixed at a ridge or apron, the overhang distance can be increased to 250 mm from the end of the sheet, as the cladding is not subjected to the same point load or UDL and the load is shared with the flashing.
Point of access and expected roof traffic loads must also be considered.
The maximum span for pan fastened wall cladding is generally governed by temporary deflection under load, rather than permanent deflection around the fastener.
|*Serviceability load governs|
|The deflection criteria used in this table is span/120 + P/20, where P = the space between fasteners. Higher deflection limits may be acceptable in certain circumstances.|
|Wind Zone||Load (kPa)*||Maximum Spans|
|0.40 mm||0.55 mm|
Fastening patterns for the most commonly used profiles are designated in the following manner.
These fastening patterns should be used in conjunction with load span graphs.
The load on a purlin and a purlin/rafter connection is determined by the wind load and the area of roof the load is acting upon. Roof fasteners transfer wind uplift-loads to the purlins, which in turn transfer them to the primary structure.
Fastening to every second purlin may be within the roof's load/span range, but will double the load acting on the fastened purlins. All purlins must be fastened to unless alternate purlins are specifically designed to take the additional loads
Wind Load span graphs should be read in conjunction with the constraint of access and the span at which the point load will be the limiting factor.
The performance of profiled metal cladding depends on the profile shape, thickness of the metal, the span, and the fastening type and pattern. These values can be greatly enhanced by using load spreading washers or thicker material.
All the tests from which these graphs have been derived used the 2:3 ratio of end to intermediate span and the graphs shown are for intermediate spans only. End spans must be reduced by two-thirds for these values to be assumed.