DESIGN mattErS BuShfIrE rESIlIENt DESIGN

SaNCtuarY88

DESIGN mattErS BuShfIrE rESIlIENt DESIGN

SaNCtuarY 89

Before you design your home, a site assessment will need to be undertaken to ascertain your property’s Bushfire Attack Level (BAL)

After the devastating 2009 bushfires in Victoria, the state government introduced a six-category Bushfire Attack Level (BAL) zoning scheme. The scheme is accompanied by Australian Standard requirements for building design and materials performance, ranging from ember protection at the low levels to fire-rated construction at the highest. Each new residential building, alteration and addition in Victoria has to meet these regulations. The rest of the country has now adopted these Standards. It’s important to talk to your building designer or architect to ensure the latest regulations are incorporated when designing your home. Andreas Sederof from Sunpower Design has recently designed a home in Musk, regional Victoria, to comply with these new standards. It will be profiled in Sanctuary 15, but here’s a preview of his experiences:

It’s important to design new and renovated country properties with the latest bushfire prevention measures, but at the same time we can incorporate best practice environmentally sustainable design. These two objectives can have a symbiotic relationship. Before you design your home, a site assessment will need to be undertaken to ascertain your property’s Bushfire Attack Level (BAL). This will determine the construction and material requirements that must be incorporated in the design and build. The BAL assessment takes into account a range of factors, including the Fire Danger Index, land slope, and surrounding vegetation type and proximity to the building. The highest risk sites are assessed

at a BAL level of FZ (Flame Zone), while the lowest are BAL-LOW. Most properties will fall under this latter level. In my experience, the designer needs to balance design freedom and the most suitable materials against the bushfire risk category of the site. It’s important to stress that “passive” bushfire protection mechanisms, such as mandated construction methods and material selection, have priority over “active systems” like roof sprinklers and pumps. History has repeatedly demonstrated that active systems can fail in an emergency due to inadequate water supply, insufficient maintenance and power failures. These systems require you to be present to activate them, which is of no benefit if you decide to leave early or the day before. When you’re designing a home for bushfire resistance, the ability to withstand the temperature (radiant heat) of the fire and ember resistance are the most important factors to consider. Minimising bushfire fuel around the home is also critical. Most house fires start sometime after the fire front passes through. Roof vents and other roof penetrations require special cowls and screens to protect the roof space from smouldering embers. The best way to ensure that cinder penetration does not become a problem is to incorporate high levels of draught proofing into the design of the building. This is also a feature of energy efficient homes, designed to prevent air leaks and heat loss. It’s also important to consider the most vulnerable external surfaces of a building. The selection of appropriate

external cladding materials can vary from highly fire resistant materials like AAC block work through to corrugated iron and in some cases very dense bushfire resistant hardwoods. Many of these dense hardwoods can be used quite successfully provided they are balanced to the site’s BAL. Windows and glazed doors, due to their relatively low thermal properties, are approximately five to six times more vulnerable to radiant heat when compared with other external construction materials. Windows are also vulnerable to airborne debris launched during a firestorm. A solution for this is to place metal shutters over the windows, either sliding or hinged. Aluminium clad, double glazed and thermally broken window frames are available on the market that easily meet BAL 29 requirements and perform well thermally in both summer and winter. [Ed note, see the boxed text on the opposite page for more information about windows.] I recently designed a home in Musk, Victoria, with a BAL rating of 40. The design solution includes tilt panel concrete walls facing the aspects that have to cope with the most severe wind and heat conditions, in this instance from the north to the south west. The aluminium framed double-glazed windows and the tiled concrete deck with steel pergolas work both aesthetically and architecturally, while decreasing the opportunity for cinder penetration. An on-ground concrete slab is essential to prevent flying embers from getting underneath the building; it also serves to maintain low internal temperatures – very desirable on extremely hot bushfire days. Roof structures should ideally be pitched metal with no box

D The bushfire resistant house built in Musk by Sunpower Design. It has a BAL site rating of 40.

Words AnDreAS SeDerof

Andreas Sederof details his experience of the updated Australian Standards for bushfire resilient design in Victoria with a recent rural new build.

BuShfIrE rESIlIENt DESIGN

GettinG GlazinG riGht for bushfire-prone buildsIn much of Australia, summer means high bushfire risk. Windows can be a weak point in the ability of the building envelope to withstand bushfire, so when you’re building in a fire-prone area, it’s important to consider framing materials, glazing type and other window treatments carefully to maximise your house’s chance of making it through if that terrible day arrives. For windows, the new Australian Standard requirements range from installing thicker toughened glass to bushfire shutters or bushfire-approved window frames. In Sanctuary 12, we profiled a house in bushfire-prone Neerim East, Victoria. Although the build predated the BAL scheme, the owners’ choice of 6mm toughened, double-glazed windows gives the house a head-start in terms of fire resistance. Remember to choose your window frame material carefully too. Aluminium or steel frames meet most

requirements for bushfire protection (but may not provide your desired thermal performance). It’s still possible to have timber window frames even in fairly high fire-risk areas; there is a small list of Australian hardwoods that will meet higher BAL requirements, including Blackbutt and Spotted Gum. Windows are available in the market for BAL 40 in timber (Paarhammer), aluminium clad timber (Miglas) and aluminium (Trend) and there are also bushfire shutters available on the market for BAL-FZ — Anna Cumming

More inforMation:– ReNew magazine windows buyers’

guide: www.renew.org.au/buyers-guide – Window Energy Rating: www.wers.net– www.paarhammer.com.au– www.miglas.com.au– www.trendwindows.com.au– www.wildfireprotection.com.au

gutters, allowing leaf debris to be blown off readily. Leafless gutters and downpipes with leaf diverters are a good idea. Provision of adequate water storage is another example of sustainable self sufficiency and bushfire protection measures working hand in hand. Let’s face it: the lower the fire risk achieved by design and careful site maintenance, the safer you and your building will be.

Andreas Sederof is a building designer and a director of Sunpower Design, a Melbourne-based consultancy and design practice specialising in integrated solutions for energy efficiency and sustainable building design. www.sunpowerdesign.com.au

More inforMation:www.buildingcommission.com.au The Building Commission publishes information about the BAL ratings as well as a PDF guide for homeowners looking to retrofit their homes for better protection from bushfires.

www.builditbackgreen.org/bushfires Created by Green Cross Australia, the Build It Back Green website is designed to help Victorian communities recovering from the Black Saturday bushfires rebuild their homes in an affordable and sustainable manner.

www.wewillrebuild.vic.gov.auVictorian Bushfire Reconstruction and Recovery Authority