KEYNOTE SPEAKER

Development of Standards for Australian Steel Framed Houses Subject to Wildfire Attack 

In 2009, following a major wildfire in Victoria, Australia, where 173 lives were lost and over 2,000 houses and 3,500 buildings were affected, including more than 2,000 destroyed, the National Association of Steel-Framed Housing, Inc. (NASH) investigated options for the safer design of houses subject to wildfires and constructed with cold-formed steel (CFS).

A review of the Australian Standard AS 3959, Construction of Buildings in Bushfire Prone Areas, was undertaken, and no benefits were given to houses constructed from non-combustible materials. AS 3959 is based upon envelope protection, which protects the house from embers and heat from the wildfire and provides weatherproofing and insulation to the house. It was also based on using a modified standard fire test to determine the suitability of the outer envelope system for the house. AS 3959 specifies bushfire attack levels (BAL) for different fire loads, depending on the types of vegetation surrounding the house. The standard BALs are 12.5, 19, 29, 40 and Flame zone (FZ), which represents the heat load of the building in kilowatts per square meter. Different design requirements are set for each BAL.

Over 80% of house fires resulted from ember attack, rather than heat loading. Also the heat curve for a wildfire bears no resemblance to a standard fire test. The house chosen as an archetype for this study represented a typical rural house and consisted of a:

• Steel clad roof supported by a steel frame/truss
• Brick veneer or light-weight wall cladding with steel framing
• Concrete slab on ground or elevated steel subfloor
• Typical non-combustible glass or mineral wool to meet energy efficiency requirements.

It was considered that this form of construction would provide a robust, economical solution for a house constructed in areas subject to wildfire attack, since both the exterior claddings and exterior cavities were constructed from non-combustible materials. This reduced the risk of combustion as the embers would not cause any issues unless they reached the internal part of the building.

A full-scale burn-over test was performed by CSIRO on a small house with a realistic heat profile, and the structure performed well. It highlighted some deficiencies, which were addressed and then subjected to small-scale fire tests. In addition, fire engineering was used to design and specify various details. The results of this work was incorporated into a NASH Standard for non-combustible construction in wildfire areas, which runs in parallel to the Australian Standard AS 3959. The NASH Standard for Steel Framed Construction in Bushfire Areas 2021 offers significant cost savings particularly at higher BAL levels. The NASH Standard provides solutions for non-combustible construction of:

• Roof systems with non-combustible cladding
• Wall systems including windows and doors
• Floor systems
• Carports, pergolas, verandahs, and decks
• Detached garages and sheds.

Ken Watson
National Association of Steel-Framed Housing Inc.

Ken Watson is the Executive Director of the National Association of Steel-Framed Housing (NASH), which is the Australian industry association for the use of cold-formed steel (CFS) in buildings. NASH covers all building types using CFS including detached housing, town houses, row houses, aged care facilities, schools, hospitals, hotels and apartments. Traditionally, NASH has concentrated on low-rise buildings but is expanding its activities into mid-rise construction.

Watson is Chairman of the NASH Standards Committee, which is responsible for developing Standards for the steel framing industry that are subsequently referenced in the Australian Building Code. These standards cover structural design and design for wildfires for steel-framed buildings. With the move into mid-rise construction, research is currently being undertaken by Australian Universities into fire design, acoustic design, structural design and robustness, which will be incorporated into NASH Standards and Handbooks.