Construction of buildings in bushfire prone areas

AS 3959:2018 specifies the construction requirements for buildings built in bushfire-prone areas in order to improve the buildings resistance to bushfire attack including from burning embers, radiant heat and flame contact or a combination of these.

The primary objective of this Australian Standard is providing a measure of protection for the occupants of buildings until the fire front passes, as well as providing a measure of protection to the building itself.

This Standard does not provide a guarantee the building will survive a bushfire attack on every occasion.

What's included

AS 3959:2018 contains nine sections: 

• Section 1: Deals with the scope, the objectives of the standard and how it should be applied - It also covers other Australian Standards that are referenced, relevant definitions of words and terms used in the standard, a flowchart on how to determine construction requirements and explains the Bushfire Attack Levels (BALs).
• Section 2: Provides information and a procedure - on how to determine the BAL of any given site, vegetation classification and the slope of sites. It also provides diagrams of various forms of vegetation for easy identification.
• Section 3: Covers the general requirements - that may apply through all BAL levels. It deals with attached and adjacent structures, decorative mouldings, gaps and screening materials, bushfire shutter requirements, glazing and sarking and also the requirements if using timber logs in construction.
• Section 4: Deals with BAL Low requirements - and just notes there are no bushfire construction requirements under BAL-Low.
• Section 5: Provides the construction requirements for BAL 12.5 - which is concerned with ember attack. It covers the construction requirements for the sub-floor through to the roof including windows and external doors.
• Section 6: Provides the construction requirements for BAL 19 - which is concerned with both ember attack and increased heat flux and covers the same building elements as BAL 12.5.
• Section 7: Provides the construction requirements for BAL 29 - which deals with both ember attack and increased heat flux and covers the same building elements as the other BALs.
• Section 8: Provides construction requirements for BAL 40 - where the concern is for both ember attack, increased heat flux and the likelihood of direct flame contact to a building and covers the same building elements as the other BALs.
• Section 9: Covers the most extreme bushfire attack level BAL Flame Zone (BAL FZ) - This is where direct flame contact will occur as well as ember attack and heat flux. The construction requirements covered under BAL FZ are the same as the other levels but it is important to note that for some elements there are no construction solutions and compliance is determined through testing standards.

This standard also contains eight appendices:

• Appendix A provides a worked example on how to complete an assessment to determine a BAL
• Appendix B provides a more detailed method for determining a BAL and would generally require specialist knowledge
• Appendix C provides a flow chart on the process around determining the BAL level using the simplified method
• Appendix D provides various illustrations to assist in the application of the Standard, and a more detailed explanation of BAL levels
• Appendix E provides information on timber species and timber densities for use in bushfire construction in conjunction with section 5 of this standard
• Appendix F provides information on timber species and timber densities for use in bushfire construction in conjunction with section 6 of this standard
• Appendix G Provides informative explanation on bushfire attack levels
• Appendix H provides generic roof construction system details for roofs that can be used in BAL FZ (or lower BALs) for both a tile and sheet roof.

This Standard is referenced in both Volume 1 and Volume 2 of the National Construction Code (NCC) providing Deemed-to-Satisfy Provisions for the construction of buildings and structures in bushfire prone areas.

Related Australian Standards

• AS 1530 Methods for fire tests on building materials, components and structures,
  • Part 1 combustibility test for material
  • Part 2 test for flammability of materials
  • Part 4 fire resistance tests of elements of construction
  • Part 8.1 tests on of construction of buildings exposed to simulated bushfire attack – Radiant heat and small flaming sources
  • Part 8.2 Tests on elements of construction for buildings exposed to simulated bushfire attack – Large flaming sources.