NZS 3604
NZS 3604 is an acceptable solution for compliance with the NZBC for light timber frame buildings not requiring specific design. It contains prescriptive dimensions for purlin spacings and fasteners , based on maximum design wind speeds of Low ( 32 m/s ) , Medium ( 37 m/s ) , High ( 44 m/s ) , Very High ( 50 m/s ) , or Extra High ( 55 m/s ) .
Some limitations of the scope of NZS3604 are:
- Timber frame construction .
- Height from lowest ground to the highest point on the roof not to exceed 10 m .
- A snow load not exceeding 1.0 kPa ( although Section 15 of NZS 3604 does provide additional criteria for 1.5 kPa and 2.0 kPa snow loads).
- private dwellings, hostels, hotels and nurse's homes ,
- factories with restricted floor loadings , and
- institutional and educational buildings with restricted floor loadings .
- buildings dedicated to the preservation of human life ,
- buildings which may host crowds ,
- publicly owned buildings containing high value contents , and
- curved roof construction .
NZS3604 uses conservative figures to arrive at a design load. Th e NZ Metal Roof and Wall Cladding Code of Practice uses the same philosophy to prescribe a value known to perform , either historically or by test , and will comply with the NZBC.
The price for this conservatism is small in comparison the overall cost of the whole of the building, and unless the building is specifically designed, designers and contractors should not deviate from the loading requirements of this section of the Code of Practice.
Classification of Wind Zones in NZS 3604 are specific to the site, because the buildings covered by this standard are limited in size. Design tables (but not design wind speed) include a local pressure factor of 1.5 over the entire structure rather than varying factors according to the position on the roof. ( see section 3.3.2 )
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