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.
3.16.5 Wind Load Span Graphs are determined by tests to criteria set out in current Standards or some accepted criteria that are derived from them, and some interpretation of the test results is necessary to fairly evaluate the capability of the product and system being tested. The wind load static tests are intended to simulate actual loads and to simulate wind uplift conditions, whereas cyclic loading would more fairly represent the conditions likely to be experienced over the life of the roof.
Normally a number of tests is carried out to give the testing authority or manufacturer confidence and a feel for his product. The number of tests and the CoV detemines the use of the statistical reduction factor. Statistical methods and the analysis of variance are used to provide data to base manufacturers' performance claims. The results are usually conservative and known rare roof failures have either not followed manufacturers' recommendations or the good trade practice described in this Code of Practice.
Wind Load span graphs can be misleading unless they are well presented and qualified by the method used to obtain them. For pierce fastened profiles, the load should be presented in kPa as a serviceability design load.
The 3.16.5 Wind Load Span Graphs represent a conservative value at which all profiles manufactured in New Zealand within the specifications noted will comply with the NZBC.