A window schedule can look sorted until the planning documents identify a bushfire requirement. So, what is a BAL rating? It is a Bushfire Attack Level used to indicate the potential exposure a home may face from ember attack, radiant heat and, at the highest level, direct flame contact during a bushfire. For a new build, extension or major renovation, the BAL affects far more than the glass you choose. It can change the required window system, screen type, door construction and installation details.
For Melbourne homeowners and builders, getting the BAL requirement right early helps avoid costly specification changes once windows and doors are already ordered. It also helps you compare products on the details that matter: compliance, glazing performance, security and lead time.
A BAL rating is a building requirement, not just a product feature
A BAL is assigned to a building site or development area following a bushfire assessment. It considers factors such as the surrounding vegetation, slope, distance from vegetation, bushfire danger index and the location of the proposed building. The higher the number, the greater the expected bushfire exposure and the stricter the construction requirements.
This distinction matters when purchasing aluminium windows and doors. A supplier may offer a BAL-rated product or configuration, but the correct product still depends on the BAL nominated for your specific project. A BAL 19 window is not automatically suitable for BAL 40, and standard double glazing does not automatically make a window bushfire compliant.
In Victoria, bushfire construction is generally assessed against Australian Standard AS 3959 and relevant National Construction Code requirements. Your building surveyor, designer or bushfire planning consultant should confirm the BAL before you lock in your glazing schedule. If your site is affected by a Bushfire Management Overlay or sits near grassland, scrub or forest, do not assume a standard window specification will be enough.
What the BAL levels mean
BAL levels are expressed as BAL-Low, BAL-12.5, BAL-19, BAL-29, BAL-40 and BAL-FZ. The figures refer to increasing radiant heat exposure, measured in kilowatts per square metre. BAL-FZ means Flame Zone, where direct flame contact is possible.
- BAL-Low means there is insufficient risk to require specific bushfire construction measures under AS 3959.
- BAL-12.5 addresses ember attack, with basic measures designed to reduce the chance of burning debris entering the building.
- BAL-19 covers ember attack and higher radiant heat exposure. Window and door requirements become more specific.
- BAL-29 requires greater resistance to radiant heat, with tighter controls around glazing, screens and openings.
- BAL-40 applies where exposure is more severe. Products and construction details need to withstand very high radiant heat.
- BAL-FZ is the highest category. Construction must deal with ember attack, radiant heat and possible direct flames, often requiring specialised tested systems.
How is a BAL rating determined?
A BAL assessment is site-specific. Two homes in the same suburb can have different BALs because one backs onto dense vegetation, sits on a slope or is closer to a bushfire hazard.
The assessment generally reviews the vegetation type and condition, the distance between vegetation and the proposed home, the effective slope under the vegetation, and the Fire Danger Index for the area. The building’s location on the block can also matter. Moving the home, garage or habitable rooms further from vegetation may reduce the assessed BAL in some projects.
Do not use a neighbour’s BAL, an old planning report or an online estimate as the final answer for your project. Vegetation, site plans and regulations can change. The documented BAL in your approved plans or bushfire assessment is the figure your window and door supplier needs.
What a BAL rating means for windows and doors
Windows and external doors are vulnerable points in a bushfire because they include glazing, frames, seals, gaps, moving panels and openings. Bushfire compliance is about the complete installed assembly, not one component in isolation.
At lower BAL levels, the focus is commonly on preventing embers from entering through openings and protecting vulnerable materials. At higher levels, the glass itself, the method of screening, frame materials, hardware and clearances can all become critical. Requirements may apply to fixed windows, awning windows, sliding windows, bi-fold windows, sliding doors, French doors and bi-fold doors.
Aluminium framing is often a practical choice for bushfire-prone projects because aluminium is non-combustible. However, an aluminium frame alone does not establish BAL suitability. The selected glass, sash design, seals, rollers, flyscreens, security screens and installation method must be considered as part of the system.
Glazing is only one part of compliance
Glass selection can change at different BAL levels. Depending on the required rating and the window location, a project may need toughened glass, a specific glazing configuration or protection through an appropriate external screen or shutter. The rules can vary according to the size of the glazed panel and the type of opening.
Double glazing has clear benefits for thermal comfort and noise reduction, particularly in Melbourne homes. It can help reduce heat loss in winter and improve comfort near large glazed areas. But it should not be specified as a substitute for BAL compliance. A double-glazed unit must still be assessed as part of a compliant window or door system for the nominated BAL.
Screens, gaps and opening details matter
Standard insect flyscreens are not necessarily bushfire screens. Where ember protection is required, the screen material, mesh aperture, fixing method and coverage need to meet the applicable construction requirements. Fine metal mesh and properly enclosed openings are commonly part of the solution, but the correct approach depends on the BAL and product design.
Sliding doors and bi-fold doors deserve particular attention because they involve larger openings and multiple moving components. A good specification should account for how panels close, how tracks are sealed, whether screens are required and whether the complete door system has evidence of suitability for the project’s BAL. Larger doors can still be achievable, but they need to be selected early rather than treated as a late upgrade.
Choosing the right window and door specification
The most efficient approach is to provide your BAL information before requesting a quote. Include the rated level, building plans, window schedule, opening sizes and preferred configurations. This allows the supplier to identify suitable systems before price and lead time become the deciding factors.
For each window and door, check whether the proposed configuration suits the project BAL, not just whether the frame looks similar to a compliant product. Ask what glazing is included, whether screens or shutters are required, and whether the supplied system is appropriate for fixed, sliding, awning or folding applications. Your builder and building surveyor should also confirm that the installation details align with the approved documentation.
There can be trade-offs. A higher BAL may mean fewer profile options, heavier glazing, more specialised screens and a higher upfront cost. On the other hand, specifying correctly from the start can prevent replacement costs, approval delays and site hold-ups. For projects that also need better insulation, sound control and secure multi-lock hardware, it is worth coordinating those performance requirements in one window and door schedule.
Get the BAL details sorted before ordering
A BAL rating should be treated as an early design input, alongside opening sizes, energy ratings and budget. It affects the products that can be used and may affect how quickly they can be supplied, particularly where a custom BAL-specific configuration is required.
Windows Doors Instock & Replacement can assist with practical aluminium window and door options once the project BAL and sizes are confirmed. Bring the documentation to the quoting stage, then you can select products that suit the site, the building approval and the timeline without making assumptions about compliance.
The right window or door is not simply the one that fits the opening. On a bushfire-prone site, it is the one that fits the opening, meets the documented BAL and still delivers the security, comfort and everyday performance your project needs.