Cyclonic Building Design

Contrary to popular belief, designing buildings for cyclonic conditions is vastly different to designing buildings for non-cyclonic regions. Designing a metal roof system in a cyclonic region should withstand the low - high - low pressure sequence that is experienced by wind loads resulting from the passage of tropical cyclones across a building. Also, other factors such as high intensity rainfall involves changing many engineering facets of the building design.

In light of this, Wide Span Sheds designs each and every steel kit building to suit specific site design criteria, including the wind region in which the site is located.

View our range of cyclone rated sheds.

Australian Wind Regions

Australia nominates their wind regions as either A, B, C or D. The nominated region required for any building will generally be dictated by the local council for the specific area in which the structure is to be built upon. The Australian Standard 1170 pre-defines wind regions for the country. The wind region has nothing to do with surrounding domain or buildings.

Australian Wind Classifications Map

What Needs to be Considered?

Before you buy a building that needs to withstand cyclonic conditions use the below information as a check-list. 

  • Make sure that you are buying a fully bolted frame shed that uses Z purlins with cleats and not top hats. 
  • Make sure your supplier is providing your purlins and girts with a minimum of 10% of the bay width + an additional 100mm overlap (this is a requirement of the manufacturers).
  • Low - High - Low Testing: The building code of Australia (BCA) in May 2009 introduced a requirement that all metal roofing systems in cyclonic areas undergo a standardised cycle test method. The LHL test is applicable to metal roof cladding, it’s fasteners and immediate support members.
  • Ensure your building uses Z purlins and girts. You will also need to ensure that the purlin and girt spacings are decreased to suit the design criteria for your area.
  • The design criteria of your building typically should be designed to a minimum Terrain Category of 2.5 in most cyclonic areas.
  • The design criteria of your building typically should be designed to a minimum Importance Level 2 in most cyclonic areas.
  • Shielding factors in cyclonic areas should typically nearly always be 1.0. Be careful of suppliers using a shielding factor of anything less.
  • Check the weight of the building that you are comparing. If there is a large discrepancy in price remember it is probably to do with the mass of steel in the building. Nothing is more expensive than a building that falls over and becomes a hazard to property and life.
  • Ensure that your building is being supplied with 0.47 TCT (Total Coated Thickness) sheeting for both roof and walls.
  • Roof screws should be Class 4 and supplied with cyclonic washers to suit your area.
  • Ensure that your building is designed to +0.7 CPI (Internal Pressure Coefficient).
  • Roller doors should be provided with an engineer certified Windlok kit to prevent them failing in a storm.
  • What is the fixing method used? Be careful of suppliers using dyna bolts for structural columns as they are not approved by the BSA and Australian standard.
  • It is important to use bridging where required. When added to portal frames, bridging significantly reduces the role of the purlin.
  • All Wide Span Sheds buildings are supplied with larger flashings and higher gutters to cope with increased winds and rainfall in your area.
  • Cyclonic sheds and homes have a ridge cap designed to be cut into suit the profile roof sheeting to stop water ingress.


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