Bushfire Attack Level (BAL) Impact on Building Services

What You Need to Know

If your site is in a bushfire prone area, every building service is affected. AS 3959 (the Australian Standard for construction in bushfire prone areas) sets rules for how pipes, ducts, vents, and external equipment must be built. The Bushfire Attack Level (BAL) rating for your site determines how strict those rules are. Miss them, and the certifier will reject the build.

• Every opening in the building envelope must be screened with corrosion-resistant metal mesh, maximum 2 mm aperture (AS 3959:2018, Cl 3.6)
• Water and gas supply pipes must be metal above ground, extending 400 mm into the wall and 100 mm below ground (AS 3959:2018, Cl 3.7)
• External air conditioning units must have all air intakes and exhausts shielded with non-combustible mesh at 2 mm aperture (AS 3959:2018, Sections 5-9)
• Evaporative coolers need ember guards at BAL-12.5 to BAL-29, must be tested to AS 1530.8.1 at BAL-40, and are prohibited at BAL-FZ (AS 3959:2018, Sections 5-9)
• A 10,000 L minimum water supply for firefighting must be on site, in a non-combustible tank at least 6 m from the building (NCC 2025, Part 3.7.4)
• All gaps greater than 2 mm in the building envelope must be sealed with non-combustible material to block ember entry (AS 3959:2018, Cl 3.6)

Take a residential aged care facility (Class 9c) on a site rated BAL-29. Every duct penetration through the roof and walls needs ember-proof sealing. The split system condensers outside need 2 mm stainless steel mesh over their air intakes. Plastic condensate pipes are not compliant, so you switch to copper. The evaporative cooler option is still available, but each unit needs a full non-combustible enclosure or ember guard, depending on whether the body is plastic or metal.

At BAL-40 or BAL-FZ, the design changes sharply. At BAL-40, evaporative coolers must be tested to AS 1530.8.1 or fitted with approved non-combustible enclosures. At BAL-FZ, they are prohibited outright. External AC units need manufacturer documentation proving non-combustible casings, or they must also be tested to AS 1530.8.1. Ducted systems with the main unit inside the building envelope become the safest compliance path. Solar panel roof penetrations must be sealed with non-combustible material and fire-rated collars.

For Class 9 buildings above BAL-12.5, the NCC does not allow the standard deemed-to-satisfy pathway. You need a Performance Solution under G5P2, which means a bushfire consultant and peer review. Budget for this early. It adds both time and cost to the design program.