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.
While the adoption of the joint Loadings Code AS/NZS 1170.2 - Structural design actions (in many revisions), has resolved many of the issues relating to the determination of wind forces on buildings, New Zealand and Australia use somewhat different testing methods and performance benchmarks, although still based on AS 4040 and providing complance with AS/NZS 1170.2.
C 1.2 Provision for variability of results
For self-supporting and fully supported secret-fixed roof and wall cladding the variability which occurs from small but significant differences in profile or clip tolerances means that a greater CoV is needed and this is generally taken for such products as 10%.
Extensive testing both static and cyclic on standard profiles with varying fastening patterns have validated the variability values given in 17.1.1A Variability Factors.
The factors in 17.1.1A Variability Factors are the same as those found in AS/NZS 1170 and AS/NZS 4600.
C.1.3. RESISTANCE TO CONCENTRATED LOAD
The requirements and general descriptions are taken from AS/NZS 1170. The method is taken from AS 4040.1
The division of Type 2 is taken from the NZMRM Code of Practice.
C.1.4 RESISTANCE TO WIND PRESSURES
AS/NZS 1170.0:2011 defines Serviceability as the Ability of a structure or structural element to perform adequately for normal use under all expected actions
The main function of a roof or wall is to provide a durable weathertight membrane and, therefore, serviceability is the ability to continue to provide a weathertight seal where the fixings penetrate through the cladding under maximum design load. For a Uniformly Distributed Load, this requires finding the applied load under which sufficient permanent deformation occurs that may cause loss of a weather seal at a fixing location. This is regarded as a serviceability failure.
Any buckling from point load that impairs the ability of the profile to be able to carry the same repeated load is also regarded as a serviceability failure.
From these definitions of serviceability for roof and wall cladding serviceability failure is considered the most important performance criterion, rather than Ultimate failure where the roof would blow off or a person would fall through it. Testing of pierce fastened profiled metal roofs has determined that failure under serviceability loads occurs at less than half the load at which strength load failure occurs. Hence serviceability load failure is considered the most important criterion for such roofs.