S-03Loads and fire
Wind and fire reach a farm shed by different routes. For wind, the building code gives every building an Importance Level, and that level sets how rare a wind the building must be designed to resist. For bushfire, the code’s construction rules reach a Class 10a shed when it is associated with a house, and set no bushfire-specific requirements for Class 7 and 8 buildings, though NSW planning rules still ask questions of them.
General information, not engineering or legal advice. Wind and fire design for a particular shed is done by its designer and checked through the approval.
Under clause B1D3 of the NCC, wind actions on a building are worked out by assigning it an Importance Level, finding the annual probability of exceedance that goes with that level, and applying the wind loading standard AS/NZS 1170.2. An annual probability of 1:500 describes a wind with a 1 in 500 chance of being exceeded in any one year: the rarer the event, the stronger the wind the design has to allow for.
| Level | Buildings the NCC describes | Non-cyclonic wind, annual probability |
|---|---|---|
| 1 | “Buildings or structures presenting a low degree of hazard to life and other property in the case of failure” | 1:100 |
| 2 | Buildings or structures not included in Levels 1, 3 and 4 | 1:500 |
| 3 | Buildings or structures designed to contain a large number of people | 1:1000 |
| 4 | Buildings or structures essential to post-disaster recovery or associated with hazardous facilities | 1:2000 |
The NCC does not place farm sheds in a level by name; the table gives descriptions, and the level for a particular shed is chosen in its structural design. The full table also sets separate figures for cyclonic wind, snow and earthquake.
In cyclonic areas, metal roof cladding, its connections and the members that directly support it must also comply with the NCC’s Specification 4. Which areas count as cyclonic changed between editions: NCC 2025 names wind regions B2, C and D under AS/NZS 1170.2, while the national text of NCC 2022 names wind regions C and D (Western Australia’s NCC 2022 variation already included B2). Sheet 02 shows which edition applies in each state. The wind regions themselves are mapped in AS/NZS 1170.2, which this guide does not reproduce.
For a Class 7b building, the NCC’s permanent actions include a notional additional roof load of not less than 0.15 kPa, so that solar panels can be added later. It does not apply where all of the roof is shaded for more than 70% of daylight hours, where the roof area is not more than 55 m², or where more than half the roof serves as a terrace, carpark, roof garden, roof light or something similar. NCC 2022 carries the same requirement and exemptions. A shed classed 7b on Sheet 02 carries this load in its design.
In a designated bushfire prone area, NCC Volume Two’s bushfire provisions apply to “a Class 1 building or a Class 10a building or deck associated with a Class 1 building”. Its Deemed-to-Satisfy route is construction to AS 3959 or to the NASH Standard for steel-framed construction in bushfire areas; in NSW both are as amended by Planning for Bush Fire Protection.
In NCC Volume One, the bushfire Performance Requirement applies to Class 2 and 3 buildings, to certain Class 9 buildings such as health-care buildings, early childhood centres and schools, and to a Class 10a building or deck immediately adjacent or connected to one of those. Class 7 and Class 8 buildings, the classes of a farm building or farm shed, are not on that list.
In NSW, development proposed on land the RFS Commissioner has certified as bush fire prone must take bush fire into account and comply with Planning for Bush Fire Protection 2019, which the planning regulations adopted on 1 March 2020, the NSW Rural Fire Service explains. Whether your land is mapped can be checked with the RFS’s own tool or on the NSW Planning Portal.
In a bush fire prone area, Planning for Bush Fire Protection 2019 leaves a Class 10a building alone when it stands more than 6 m from a dwelling: there are no bush fire protection requirements for it. Closer than 6 m to a dwelling, it has to be built to the NCC.
For Class 5 to 8 buildings, Planning for Bush Fire Protection notes that the NCC has no bush fire specific performance requirements, so AS 3959 and the NASH Standard are not Deemed-to-Satisfy provisions for them, though compliance with both must be considered when meeting the document’s aims. It then applies objectives on four things: safe access to and from the public road for firefighters and for evacuation, emergency and evacuation arrangements for occupants, water for protecting buildings with gas and electricity placed so as not to add to the fire risk, and storing hazardous materials away from the hazard wherever possible. Construction requirements for bush fire protection are considered case by case.
CFA explains that the Bushfire Management Overlay applies to land in Victoria that may be at risk from bushfire, and that if a property is within it you will likely need a planning permit to develop or subdivide. Permits are granted only when CFA and the responsible authority, normally the council, are satisfied the proposal meets the bushfire policies in the Victoria Planning Provisions. CFA’s page sends general questions about a permit to the local council.
This sheet does not explain Bushfire Attack Levels (the BAL ratings in AS 3959). In NSW, the Rural Fire Service page linked above has a tool for checking whether land is bush fire prone; in Victoria, CFA sends planning permit questions to the local council.