Understanding Bushfire Attack Level ratings and compliance for decking

Decks in bushfire-prone areas leave no room for guesswork. BAL rules determine which timbers, composites, and fixings can be used and how the deck must be assembled. AS 3959 and the NCC outline these requirements across Sydney and NSW. Abbey Timber helps installers meet them with compliant hardwoods, tested composites and consistent stock.

How BAL ratings are worked out

A BAL rating is determined through a site assessment that considers three factors.

1. The type and density of nearby vegetation.
2. The distance from the building site to the vegetation.
3. The slope between the site and the vegetation.

These inputs shape the potential fire behaviour at the site. According to the NSW Government Planning Portal, new building work in mapped bushfire-prone areas needs a BAL assessment to confirm compliance with AS 3959 and the National Construction Code. Installers across Sydney most often work in BAL-12.5, BAL-19 and BAL-29 zones.

What each BAL level means for decking

BAL-12.5 focuses on ember attack. Decks can use many Australian hardwoods and some certified composites, but gaps, junctions and subfloor areas still need controlled detailing.

BAL-19 increases expected heat exposure. Fixings, gap tolerances and cavity closure become more important.

BAL-29 has stricter limits and often requires non-combustible or low-combustible elements in the substructure. Many softwoods are excluded unless tested. Composites must carry evidence of testing to AS 1530.8.1 or an equivalent bushfire performance test recognised under the National Construction Code.

These requirements come from AS 3959, which is referenced by the NCC as the governing bushfire construction standard. Installers often allow for extra labour and tighter tolerances in higher BAL zones.

Choosing materials that meet BAL rules

Australian hardwoods such as spotted gum, blackbutt and ironbark are suitable for higher BAL levels due to their density and fire behaviour. Abbey Timber’s timber decking range includes many bushfire-resistant species rated to BAL-29 and BAL-19.

Composite decking boards can be used in some BAL zones when they have certified bushfire test data. Many councils and certifiers require documentation that shows compliance with AS 1530.8.1 and AS 3959.

Non-combustible materials, such as aluminium or steel subframes, are often used in BAL 29 and above because they meet the NCC pathway requirements for non-combustible construction.

Build details that influence compliance

Correct installation is a major part of complying with AS 3959 and the NCC bushfire provisions. Ember protection, gap sizing, and cavity closure must match the BAL rating. Installers often use metal mesh under the deck with the required aperture size to block embers.

Stainless steel fixings are commonly used because they handle heat and resist corrosion. Ventilation, drainage and junction detailing help prevent debris build-up, which is a known ignition point. Minor issues such as oversized gaps or exposed joints often delay certification under NCC bushfire requirements. 

Maintenance expectations for BAL-rated decks

Decks in bushfire-prone areas need regular cleaning and inspection. Removing leaf litter, checking board gaps and ensuring mesh screens remain intact help maintain compliance. According to the NSW Rural Fire Service, accumulated debris under decks is a known source of ember ignition. Ongoing maintenance supports the intent of AS 3959 and NCC bushfire safety requirements.

Confirming compliance before sign off

Installers confirm that the deck matches the BAL rating listed on the building approval. Species choice, composite certification, fixings, and subframe materials must match the documented construction pathway under the National Construction Code and AS 3959. Any variation may need reassessment.

Project teams often review species data sheets, composite fire test reports and hardware specifications before final checks. Accurate documentation helps approvals run smoothly across Sydney and NSW.

In summary

• BAL ratings apply to mapped bushfire-prone areas identified by local planning authorities. BAL-12.5, BAL-19 and BAL-29 are common across Sydney and NSW.
• AS 3959, referenced by the National Construction Code, sets the construction rules for decks in these areas.
• Spotted gum, blackbutt and ironbark are suitable hardwoods.
• Composite decking in BAL zones need certified testing, such as AS 1530.8.1.
  Abbey Timber supplies hardwoods, composites and hardware suitable for BAL-regulated projects.

Abbey Timber has the largest range of decking timbers, composite decking, hardware, and tools, with fast delivery and a Sydney showroom where you can see the difference for yourself. 

If you would like more advice from one of the expert trade team at Abbey Timber, call or visit the showroom or chat to us online.

References 

https://www.rfs.nsw.gov.au/ 
https://www.planning.nsw.gov.au/ 
https://www.standards.org.au/  
https://ncc.abcb.gov.au/