BAL-29: meaning and construction requirements
BAL-29 is the middle-high Bushfire Attack Level. It means a building could face radiant heat of more than 19 and up to 29 kilowatts per square metre, with heavy ember attack. That's enough heat to crack ordinary glass, so BAL-29 adds toughened glass, heat-resistant frames and fire-resistant decks and cladding to the ember protection.
What is BAL 29?
BAL-29 is where radiant heat starts to damage a building as well as embers. Ordinary window glass can crack, letting embers in, and some timbers and plastics can ignite or fail. The requirements protect the building envelope so it holds up through the fire front.
What puts a site at BAL-29
Vegetation fairly close to the building, or bush further away on ground that falls away steeply from the house. Forest and woodland put a site at BAL-29 from further away than grassland does. BAL-29 matters beyond construction: in some states, planning rules for new subdivisions aim to keep homes at BAL-29 or lower.
A BAL determines which construction requirements apply to the building. Your building surveyor or an accredited bushfire practitioner can tell you what they are.
How state rules differ
AS 3959 sets the construction requirements; each state decides where and how they apply. In NSW, BALs are set under Planning for Bush Fire Protection. In WA, planning rules pay close attention to BAL-29, because new development is generally planned to stay at or below it. See the BAL calculator by state.
What BAL-29 costs
BAL-29 is where costs climb noticeably, mainly in windows, doors and decking. The amount depends heavily on how much glass the design has and where the deck is. Price it from your plans with your builder and window supplier before you commit to a design.
Getting to BAL-19
Moving the building further from the vegetation that sets the level is the main lever, and sometimes a few metres is enough. BAL Buddy shows the move needed for the next lower level. See how to lower your BAL. The levels either side are BAL-19 and BAL-40.
BAL Buddy gives an indicative Bushfire Attack Level (BAL) only. It isn't a determination under any Act, and no council or building surveyor has to accept it. For a BAL you can rely on, use an accredited bushfire practitioner.
Need a bushfire practitioner?
FPA Australia keeps a public register of BPAD-accredited practitioners, searchable by state and accreditation level: BPAD practitioner register. If you're not sure who to call, email me and I'll point you in the right direction. I don't take referral fees.
Questions people ask
What is BAL 29?
It's a Bushfire Attack Level for sites where a building could face radiant heat up to 29 kW/m² with heavy ember attack. It's enough heat to crack ordinary glass, so the requirements add toughened glass and fire-resistant materials.
What are BAL 29 window requirements?
In short, toughened glass in metal, fire-resistant timber or metal-reinforced uPVC frames, with metal mesh screens on the openable parts, or bushfire shutters instead. Your window supplier can tell you which of their ranges are rated to BAL-29. More on BAL windows and decking.
What are BAL 29 decking requirements?
Decking, joists and supports in non-combustible material or a fire-resistant timber, with the space underneath enclosed or kept clear. Composite and timber products need to be rated for BAL-29 by the manufacturer.
Is BAL 29 bad?
It's not a reason to walk away from a block, but it adds real cost. Check early, because the house position can sometimes bring it down to BAL-19.
What's the difference between BAL 29 and BAL 40?
At BAL-40 flames may reach the building, so windows and doors generally have to be tested systems or shuttered, and decks non-combustible. It's a much bigger step than BAL-19 to BAL-29.