The Building Code of Australia introduced – Australian Standard AS3959 – recommending 6 categories for bushfire attack levels as follows:- BAL Low, BAL 12.5, BAL 19, BAL 40 and Flame Zone.
These BAL levels determine the specific areas that are prone to bushfire attack, from let’s say zero possibility to Flame Zone (FZ). When we look at BAL Low there is not a lot of risk to warrant specific stringent construction requirements, however we should still be mindful to the possibility for wind driven embers from afar. Basically most of Australia should be aware and mindful of bushfires, due to the fact that bushfires from long distances have reached into the outer suburbs of most of our cities. So I dare say that BAL Low would refer to most of us, so we should err on the side of caution – to practice the principle of no clutter around the home – to not fuel the possibility, as most scenarios are possible.
BAL 12.5 ATTACK BY EMBERS – the requirement for ember protection within the construction of a home in BAL 12.5 will be required to meet Australian Standard AS3959 as will any retrofittings.
SO YOU SEE THE REQUIREMENTS INCREASE AS THE RISK FOR BUSHFIRE INCREASE, THE FURTHER YOU ENCROACH INTO BUSHFIRE PRONE AREAS THE RISKS INCREASE FOR STRUCTURES TO COMPLY FOR EACH BUSHFIRE BAL LEVEL.
The scenarios for the possibility of bushfires increase with further build up of trees, vegetation and foliage, so the requirements for the construction of buildings will increase accordingly.
BAL 29 ATTACK BY RADIANT HEAT AND BURNING DEBRIS – is significant enough to threaten the integrity of the construction with the probability of some flame contact. So likewise the increase for further stringent measures in construction are required.
BAL 40 THE POSSIBILITIES FOR BURNING DEBRIS AND RADIANT HEAT LEVELS ARE SIGNIFICANTLY INCREASED WITH THE HEIGHTENED PROBABILITY OF FLAME CONTACT – this could threaten the building’s integrity, therefore buildings must be constructed in a manner to enable them to withstand extreme heat with potential flame contact.
FZ – FLAME ZONE – radiant heat and flame contact are highly likely with any bushfire situation. Serious attention to the design and construction in Flame Zone, for the protection of residents with flame proof building materials throughout the building being of the highest priority. As Flame Zone goes beyond the scope of the BCA (Building Codes of Australia) local Councils usually mandate higher priorities for building design and materials including all requirements of BAL FZ when you submit your plans to build in FZ and Councils will police these requirements to completion of final – this also applies to each of the BAL ratings to comply to council approval.
MOST OF AUSTRALIA’S POPULATION LIVING IN CITIES WOULD BE BAL LOW – however we reiterate that even though the risk of bushfire is very low, we should still be vigilant, by keeping the clutter around the home to the barest minimum. Why is that? In the height of summer with temperatures sometimes above the 40’s significant radiant heat levels and with high wind conditions, embers from burning debris can travel long distances – for example:- in the 2003 Canberra bushfires, embers travelled hundreds of metres and randomly picked out houses, why was that? Why did some houses burn when the houses that surrounded them were untouched – the houses that burned hundreds of metres from the fires quite possibly had clutter in the form of trees and foliage overhanging the roof and sometimes the foliage will build up on the roof (especially pine needles) I have personally seen pine needles 200mil deep on one particular roof and that was actually the roof of one of the homes that burnt to the ground in the 2003 Canberra fires – then there is the stacking of items against the house or the fence such as firewood etc, etc. Any of this clutter is all fuel for an ember attack. Keep the perimeter of your home and fences clear of clutter especially if you live within the outskirts of a town or city. Believe me as a roofer I have seen it all and there is usually plenty of clutter around most homes.
SO YOU NEED TO KEEP THE CLUTTER CLEAR OF ALL PERIMETERS OF YOUR HOME IF YOU LIVE ON THE OUTSKIRTS OF A TOWN OR CITY, KEEP YOUR ROOF AND GUTTERS CLEAN AND ALL PROTUSIONS THROUGH YOUR ROOF EMBER PROOF.
IT IS QUITE UNBELIEVABLE AND BEYOND THE IMAGINATION TO REALISE THAT PEOPLE ARE STILL USING WHIRLYBIRDS (ESPECIALLY ALUMINIUM) IN ANY TYPE OF BUSHFIRE PRONE AREA.
Number one, they are still made of aluminium which is highly combustible. During the Canberra bushfires whirlybirds were literally sucked out of roofs like a piece of tissue paper and just imagine placing a loose ember guard in the bottom of a whirlybird as they catch burning embers that could buildup in the bottom of the whirlybird – do the equations, 40°C plus days roofspace in excess of 80°C plus whirlybird full of embers – time bomb.
Conclusion – a whirlybird in any bushfire prone area is no different than playing Russian roulette with a full magazine.
There is really only one type of roof ventilation system that truly complies to the building codes that are ember proof, noncombustible, aerodynamically designed, almost flush to the roof and do not allow any collection of any type of debris that is the Universal Tile Ventilator System. The Universal Tile Ventilator for tiled roofs and the Smoothline Ventilator for corrugated colorbond roofs.