BAL-rated decks for the Cardinia Hills.
Cockatoo. Emerald. Pakenham Upper. Beaconsfield Upper. Gembrook. Decks in the BMO must be designed to AS 3959-2018 for their BAL rating. Here’s the material, substructure and detail spec for each BAL class.
The BAL ratings, decking spec per rating.
| BAL Rating | Heat flux | Deck material spec |
|---|---|---|
| BAL-LOW | <12.5 kW/m² | No restriction |
| BAL-12.5 | 12.5 kW/m² | Class 1, 2 or 3 timber OR sealed gaps <3mm OR non-combustible substructure |
| BAL-19 | 19 kW/m² | Class 2 timber min (spotted gum, blackbutt) OR Class 1 with ember-resistant venting |
| BAL-29 | 29 kW/m² | Class 1 hardwood (jarrah, ironbark, turpentine) above non-combustible substructure |
| BAL-40 | 40 kW/m² | Class 1 hardwood OR non-combustible deck above non-combustible substructure, full ember protection |
| BAL-FZ | >40 kW/m² | Non-combustible only (steel/aluminium/concrete deck) |
What Class 1 / Class 2 actually mean.
AS 3959 timber fire-rating classes are based on density and fire performance:
- Class 1 hardwoods: Jarrah, ironbark, kwila/merbau, turpentine, blackbutt (when full hardwood). Density >750kg/m³. Highest fire resistance.
- Class 2 hardwoods: Spotted gum, river red gum, brushbox. Density 650–750 kg/m³. Good fire resistance.
- Class 3 timbers: Treated pine (H4+), pine framing. Density <650 kg/m³. Acceptable for BAL-12.5 only.
Important: AS 3959 fire class is NOT the same as the H-class treatment rating (H3, H4, H5). H-class is rot/termite resistance; fire-class is combustion behaviour.
Non-combustible substructure (BAL-29 and above).
For BAL-29+, the support structure (bearers, joists, posts) must be non-combustible OR fully encapsulated to AS 3959 detail. Options:
- Galvanised steel C-section bearers and joists. Our standard for BAL-29+ in Cardinia Hills. ~$80–$120/m² substructure cost (vs $30–$50/m² for timber).
- Concrete-encased steel stumps (always — mandatory for any BAL rating).
- Cement-sheet underdecking with ember-resistant venting (BAL-19+).
- Hardwood substructure with full board-to-board sealed underdecking acceptable in some BAL-19 builds.
Ember protection details.
BAL-29 and BAL-40 builds need ember-resistant detailing at every gap:
- Deck-to-house junction sealed with 2mm-max bronze mesh + sealant
- Underdecking ventilation through 2mm bronze mesh (no larger)
- Stair stringer sides sealed (ember-trap risk)
- Subfloor enclosed with 6mm cement sheet or BAL-rated lattice (mesh-backed)
- Any timber within 100mm of cladding line sealed against ember entry
Step 1: get the BAL rating.
Before any design starts, we get the BAL assessment done:
- Accredited bushfire consultant attends site
- Measures distance to vegetation, slope, and vegetation type
- Issues written BAL rating report
- Cost: $450–$780. Valid for the duration of the build.
- Required by Cardinia Shire planning permit and the building permit
We coordinate the BAL assessment with our regular consultants. Same week turnaround typical.
Where we work.
BAL-compliant deck, designed for your block.
BAL assessment coordinated, AS 3959 design, NCC 2022 compliant build.