The bushfires of Australia have destroyed more than 2,000 homes since the inception of the bushfire season. And in the minds of many, the question remains: Could these homes have been built with more fire-resistant structures?
A related question, of course, is if Australian building codes need to be changed and amended.
Due to the progression and enhancement of building codes over time, newer buildings seem to be more resistant to fire than previous models. And especially in the wake of the 2009 “Black Saturday” bushfire tragedy in Victoria, which claimed 173 lives and more than 2,000 homes, the codes have gotten tougher.
The development of the National Construction Code, for example, has set minimum standards for the design and building of new building structures across bushfire-prone land. The National Construction Code is based on performance, and does not indicate how a building must be constructed–simply how a building should perform. This allows for the expedient approval of innovative designs, materials and building methods.
A residential structure established upon bushfire-prone property, the code indicates, must be designed and built to lessen the risk of bushfire ignition, as per the risk generated from bushfire flames, embers, radiated heat and the strength of the bushfire attack.
A building’s risk level relies on the specific site and conditions like the variety and density of vegetation, and the slope of the land. Properties are reviewed and are granted a “Bushfire Attack Level” (BAL) rating by inspectors.
Six BAL levels serve to classify a building’s level of possible bushfire risk. The highest level – BAL FZ – is reserved for structures which may face an extreme risk, like a home surrounded by trees that could generate direct flame contact.
Lower BAL levels consider risks posed by burning debris, the attack of embers and radiant heat. The lowest level is reserved for homes with a risk too minimal to justify any particular building requirements.
Construction specifications would be needed for each BAL detail building characteristics like walls, floors, roofs, windows, doors, vents, roof drainage systems, water and gas supply pipes, and verandahs. Fire-resistant timber, for instance, might be needed for floor framing, or windows with stronger glass might be installed.
Is the National Construction Code sufficient?
If the intention is to minimise the quantity of buildings damaged or destroyed in extreme level fires, then no. However, that is not the objective of the code. The code is all about the balance of conflicting interests.
All building rules are determined by cost-benefit analysis. These regulations must display a “net cost benefit” to the community, demonstrating that the cost of compliance will be less than the benefit granted the general community.
Government policy weighs the cost of building homes in accordance with tougher building codes against the cost of losing more homes to the fires. So if analysis finds that the cost of building destruction caused by bushfires is more than the cost of developing tougher building requirements, then this could result in the establishment of those regulations.
As a result of the Black Saturday fires, changes were recommended to the National Construction Code. These included provisions to render protection from an ember attack a performance mandate; examine the design and building of private (underground) bushfire emergency shelters; and to address design and construction specifications for non-residential structures, like schools and nursing centres, in bushfire-prone areas.
All area governments accepted the first two recommendations, quickly implemented in the National Construction Code.
The recommendation regarding non-residential building was not put into place at the time because governments took into account the fact that planning laws would not permit these types of buildings to be constructed in a bushfire-prone region.
Yet the 2019-2020 business plan pertaining to the Australian Building Codes Board features a “bushfire provisions for non-residential buildings” endeavour, which should make a difference in the future. A vital, needed difference.