The bushfires in Victoria had serious ramifications for the development of new homes. Stephanie McDonald reports on what the new bushfire regulations mean for designers and builders.
As the flames were put out on the fires in Victoria this year, people were scrambling for answers. Why were the fires so devastating? Could something have been done to prevent the level of destruction? The answer to the latter question apparently was yes.
New standards were finalised in March this year and replace the 1999 standards in the BCA for homes built in bushfire prone areas.
AS 3959-2009 takes a risk management approach to design and aligns construction requirements more closely to the assessed level of bushfire exposure for new building works and renovations. Changes include increasing the four levels of risk assessment to six. The new levels of bushfire attack include:
• BAL-Low: There is insufficient risk to warrant specific construction requirements
• BAL-12.5: Ember attack
• BAL-19: Increasing levels of ember attack and burning debris ignited by windborne embers together with increasing heat flux between 12.5 and 19 kW per sqm
• BAL-29: Increasing levels of ember attack and burning debris ignited by windborne embers together with increasing heat flux between 19 and 29 kW per sqm
• BAL-40: Increasing levels of ember attack and burning debris ignited by windborne embers together with increasing heat flux with the increased likelihood of exposure to flames
• BAL- FZ: Direct exposure to flames from a fire front
“It will be important that prior to design being undertaken that architects and designers ensure that an accurate BAL assessment is undertaken to determine the best use of construction materials,” Tony Arnel says, building and plumbing commissioner at the Building Commission. “The majority of homes in Victoria will be assessed at the lowest risk level and therefore will not be subject to any specific conditions.”
According to the Building Commission, the building standard for new homes at risk of bushfire may be required to have:
• roofs, verandahs or decking made from a non-combustible material
• wall and roof joints sealed against ember attacks
• windows protected by non-combustible shutters or with 4 mm to 5 mm toughened glass
• door frames made from fire-resistant timber, tightly fitted and include a weather strip at the base
Stephen Greenwood, assistant technical director at HIA, says roofing materials such as non-combustible tile and metal can still be used but require added protection to prevent embers entering the roof space. In BAL-FZ, a roof assembly also needs to conform to stringent testing criteria.
A new roofing system which can be used in BAL-FZ was jointly funded by Forest and Wood Products Australia, Bluescope Steel and Promat Australia. The system comprises roofing made from Colorbond steel, timber roof battens, plywood insulating board, timber trusses and fire-resistant plasterboard and timber fascia, which is to be assembled and detailed in a prescribed manner.
The window industry has also been quick to respond to the new regulations. Windows are one of the most vulnerable parts of a home when it comes to fire attack, something which the new regulations acknowledge. For instance, window and door systems to be used in areas with a rating of BAL-12.5 to BAL-40 must be tested to AS1530.8.1 if they are to avoid AS3959’s requirement of external shutters or screens.
Some companies, such as Miglas, are taking some of the complexity out of the equation for designers by conducting its own independent tests and sought testing for its FireGuard 40 window. Exova WarringtonFire, which is a registered testing authority and accredited by the National Association of Testing Authorities (NATA), tested FireGuard 40 to AS1530.8.1 and AS 1530.8.2. Test results approved the product for use on sites up to and including BAL-40, meaning it can withstand 40 kW per sqm of radiant heat flux.
Trend Windows & Doors says damage from either glazing failure or door system failure allows debris to enter a building, causing ignition. As a result, Trend focused on the entire glazing system, with its Xtreme windows and doors range passing the standard test at the BAL-40 level without the need for screens to be fitted to fixed sashes.
The Australian Glass & Glazing Association (AGGA) has also released an information sheet on what the regulations mean for doors and windows. It says new requirements for windows are applicable to glazing that is less than 400 mm from the ground. Where double glazing is used, other requirements apply, such as screens (mesh with apertures no larger than 2 mm). For buildings with a risk level of BAL-12.5 to BAL-29, screens may be made of aluminium, steel or bronze. For BAL-40 or BAL-FZ, screens must be steel or bronze.
Greenwood says as far as HIA is aware, no domestic windows have been tested to satisfy the BAL-FZ requirements. However, there are commercial-type steel-framed windows that may suffice, but generally would not be used for residential applications.
Timber is another material which has come under the spotlight. “In the lower BALs there are no major changes to construction types and the use of timber in buildings. This applies to the majority of homes in Victoria. However, if a site is assessed in BAL-40 or in BAL-FZ, then timber is restricted, particularly where exposed, such as decks,” Arnel says.
Despite the misconception timber is fuel for fires, there are several types of timber that can be used in bushfire prone areas. As a result of testing carried out at Victoria University, the Warrington Fire Research Group certified several non-fire-retardant treated hardwood species (minimum thickness 18 mm) which satisfy the requirements for fire retardant treated timber in the standard. They include: Blackbutt; Spotted Gum; Red Ironbark; Kwila; Turpentine; Silver Top Ash; and River Red Gum.
Another product which can be used in the highest fire level — BAL-FZ — is Hebel’s solid and lightweight-framed systems. Its products meet or exceed the requirements in all levels, including BAL-FZ, for external walls, floors, subfloor supports, decks and verandahs.
Hebel PowerBlock provides frameless loadbearing walls and has a fire resistance level (FRL) of 240/240/240 — higher than the standards require. Hebel PowerWall uses 75 mm Hebel steel-reinforced panels on a framed construction and achieves an FRL of 240/180/180, which exceeds the requirements of BAL-FZ.
For walling, Victor Avrutis, marketing manager board and systems at Boral Plasterboard, says a 30 min fire rating of the external envelope is required only for BAL-FZ. In these zones, the company’s OutRwall and Fireclad external wall systems are suitable.
As the findings of the Royal Commission are handed down in 2010, there is no doubt manufacturers will have released more products which adhere to the regulations and make the process of building in bushfire prone areas easier for designers and builders.
