BAL-40: meaning and construction requirements
BAL-40 is the second-highest Bushfire Attack Level. It means a building could face radiant heat of more than 29 and up to 40 kilowatts per square metre, and flames from the fire front may reach it. Windows, doors and walls generally have to be tested bushfire systems or protected by shutters.
What BAL 40 means
At this level, radiant heat is intense enough to ignite many materials, and flames may briefly touch the building as the fire front passes. The building has to survive that, not just keep embers out. That's why the requirements move from prescribed materials towards systems tested for bushfire exposure.
What puts a site at BAL-40
Vegetation close to the building, especially forest or woodland, or bush on ground falling steeply away from the house.
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
In WA, a habitable building on a site rated BAL-40 or BAL-FZ generally needs development approval even where it would otherwise be exempt, and planning policy generally doesn't support new lots at these levels. Other states have their own controls. See the BAL calculator by state.
What BAL-40 costs
Costs rise sharply. Windows are the biggest item: Renew magazine reports one major window maker's estimate that BAL-40 windows cost about 28% more than standard windows. Shutters, non-combustible cladding and non-combustible decking add more. If the house position allows it, getting to BAL-29 is usually worth real effort.
Getting to BAL-29
Distance is the lever. Check whether a different position on the block moves the building out of BAL-40, and whether the vegetation that sets the level can lawfully be managed. BAL Buddy shows the move needed. See how to lower your BAL. The levels either side are BAL-29 and BAL-FZ.
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 does BAL 40 mean?
The building could face radiant heat up to 40 kW/m², and flames from the fire front may intermittently reach it.
What are the BAL 40 requirements?
Windows, doors and walls that are tested bushfire systems, shuttered, or built from prescribed non-combustible combinations; a non-combustible, fully sarked roof; and non-combustible decks. AS 3959 has the detail.
Is BAL 40 the same as the Flame Zone?
No. At BAL-40 flames may intermittently reach the building. BAL-FZ is direct exposure to flames, and the requirements are stricter again.
Can I use timber at BAL 40?
Generally not for decking or exposed cladding. Tested systems may include timber elements, so check the manufacturer's test evidence.
Can I build at BAL 40?
In most places, yes, if the building meets the requirements, though planning rules in some states make it harder. Ask your council early.