With building quality and compliance putting a significant spotlight on the industry, it has never been more important to have a detailed understanding of how the correct site wind rating impacts your building. This will ensure your building designs and construction are carried out in accordance with the NCC and relevant Australian Standards.
The site wind rating affects the design of most building elements including:
- footing size and type
- framing and member sizing
- bracing and tie down requirements
- cladding and roofing fixing requirements
- window and door types.
Even external elements, such as eave and soffit fixing and framing, as well as external waterproofing against wind driven rain, are impacted and have a specific specification based on the site wind rating.
When the wind rating is applied to these elements, it will impact the design and may even limit the design type for certain wind classes – particularly in cyclonic areas of Australia.
The framing design for a dwelling, including member sizes and maximum spans, will be influenced because the loads will vary greatly based on the relevant site wind rating.
Additionally, the bracing design, including material types, fixings, spacings and the number of bracing units for the frame, need to be specifically designed for the house based on the wind rating. For brick buildings, columns may need to be built in to support the brickwork against the wind loads.
Similarly, the fixing of the frame and tying down to the slab or sub-floor, as well as truss and roofing member tie downs, need to be specifically designed for a house. AS1684 Residential timber-framed construction and the NASH standard for lightweight steel framing sets out these requirements in the relevant span tables, and bracing and fixing requirements.
The wind rating can also limit the use of certain material types or products. For example, wind ratings of N3 or lower (that is, N1, N2 and N3) are included in a number of simplified design scenarios, such as those in the deemed to comply solutions in the NCC wall claddings.
Given these differing and critical factors for the compliance and ongoing performance of the building, it highlights how important it is to ensure the building’s design and construction is carried out to suit the relevant wind rating for the site.