Bushfire-rated windows: AS 3959 and the BAL levels
A bushfire-rated window is specified to a BAL level, not a general fire rating: AS 3959 sets six levels (BAL-Low through BAL-FZ) from the site vegetation and slope, and the window build — frame material, mesh, glazing and seals — is chosen to the site level. On our schedule the BAL case runs on the same frame lines as the standard range, with the mesh, the toughened or laminated glazing and the metal seals the level requires, and the certificate ships in the document pack.
What BAL actually is
BAL is a property of the site, not of the product. AS 3959 reads the vegetation class, the distance to that vegetation, the effective slope and the fire danger index, and returns the site BAL — from BAL-Low (no specific construction) up through BAL-12.5, BAL-19, BAL-29 and BAL-40 to BAL-FZ (flame zone). The window specification follows the level: the higher the BAL, the tougher the frame, the tighter the mesh and the less the build relies on any combustible element.
The window build, level by level
- BAL-12.5 and BAL-19: metal frames with metal or corrosion-resistant mesh screens (aluminium or stainless), toughened glass and metal weather seals — the common coastal-interface and fringe case.
- BAL-29: the mesh gauge and aperture tighten, the glazing moves to toughened or laminated with a higher fire performance, and the screening of openings and gaps is specified to the standard.
- BAL-40 and BAL-FZ: the exposed face is metal (no timber-aluminium there), screens are stainless mesh, and shutters or the equivalent protection are specified to AS 3959 — the flame-zone case is a different detail and is quoted as its own line.
Where it lands on our lines
The BAL case builds on the standard aluminium frames — CW-60, TT-75, SD-50 — with the mesh, glazing and seal schedule the site level sets, so the elevation does not change shape when the rating is added. The timber-faced WA-70 is not used on the exposed face at BAL-40 and above, because AS 3959 removes the combustible element there; on a protected elevation it can still be specified. The bushfire-adjacent regions — the NSW and Victorian interfaces, and parts of South and Western Australia — are where the schedule carries the BAL column alongside the AS 1170.2 wind zone.
How to write it on the schedule
- Read the BAL from the site assessment or the planning certificate, not from a postcode.
- Name the level per elevation — the exposed face and the protected face can carry different levels.
- State the mesh and the glazing per the level; the screen is a first-class line item, not an accessory.
- The certificate for the configured unit ships in the document pack, coordinated with a NATA-accredited laboratory.
Questions
No — it is rated to a BAL level, which describes the construction that level requires. BAL-40 and BAL-FZ add shutters or equivalent protection; the window is one part of the envelope.