Understanding BAL Ratings: What It Means, How It's Calculated, and What to Do Next

If you're planning to build in a bushfire-prone area, you’ll almost certainly come across the term Bushfire Attack Level, or BAL. It’s not just a technical classification — it’s a crucial part of ensuring your home is designed to withstand bushfire threats.

In this guide, we explain what a BAL rating is, how it’s calculated, how it impacts your project, and what steps to take once you’ve received one.

🔥 What Exactly Is a BAL Rating?

A BAL rating is a measure of how much risk a building site faces from bushfire exposure. It considers the three main ways a fire can impact a property: ember attack, radiant heat, and direct flame contact. These risks are assessed using AS 3959 – Construction of Buildings in Bushfire-Prone Areas, a national standard that determines how to classify and manage bushfire threat levels for buildings.

Your final BAL rating reflects the expected level of radiant heat exposure, measured in kilowatts per square metre (kW/m²). The higher the number, the more intense the fire risk — and the more protective measures your build will require.

Here’s a quick look at the six BAL levels:

• BAL–Low: Very minimal bushfire risk

• BAL–12.5 to BAL–29: Increasing levels of radiant heat and ember exposure

• BAL–40: High heat levels with some flame contact likely

• BAL–FZ (Flame Zone): Extreme risk, with direct flame contact expected

Even a BAL–12.5 site — often considered "low to moderate" risk — still requires specific construction adjustments to improve fire resilience.

When Is a BAL Assessment Required?

A BAL Assessment is typically required:

• When a property is located within a designated Bushfire Prone Area (BPA)—you can check this via the DFES mapping tool.

• For any new building, renovation, or development application in a BPA.

• At the time of applying for a Building Permit, and possibly when applying for Development Approval (DA), or Subdivision.

• When there is a change of land use or intensification of site use (e.g., a new dwelling, grouped housing, or commercial premises) within a BPA.

Who Can Prepare a BAL Assessment?

Only individuals accredited through the Bushfire Planning and Design (BPAD) scheme are authorised to carry out formal BAL Assessments in Western Australia. The levels of accreditation include:

• Level 1: BAL Assessments.

• Level 2: More detailed assessments including contour maps and Bushfire Management Plans.

• Level 3: Complex or performance-based assessments (e.g. vulnerable uses, non-compliant proposals).

At Bushfire Smart, our team has accredited practitioners who cover the whole suite of project needs, and are trained and experienced in applying the bushfire planning framework to both residential and commercial projects.

📐 How Is a BAL Rating Calculated?

BAL ratings are determined through a structured process that evaluates both the site and its surrounding environment. Most assessments follow Method 1 in AS 3959, which involves five key steps:

1. Fire Danger Index (FDI):
This is a measure of how likely a fire is to start and how severely it could behave under typical weather conditions. In Western Australia, the FDI is fixed at 80 for assessment purposes.

2. Vegetation Classification:
Assessors look at all vegetation within 100 metres of the building site. If it can’t be excluded as low threat (like irrigated gardens or managed lawns), it must be classified into one of seven types. Tree-dense woodlands, grassy paddocks, coastal scrub — each has different implications for fire behaviour.

3. Distance to Vegetation:
How close is the building to the nearest patch of classified vegetation? The closer the structure, the higher the exposure to embers and radiant heat.

4. Slope Under Vegetation:
Slope is a major factor. Fires move faster uphill, so steeper ground beneath vegetation increases the level of risk. As a rule of thumb, a fire's rate of spread doubles with every 10° increase in slope!

5. Final BAL Determination:
All this data is plugged into a set of tables in AS 3959. The vegetation plot that poses the greatest risk becomes the basis for the site’s BAL rating.

This method ensures that the most threatening conditions near the building site are factored into the final outcome — giving you a practical, risk-informed rating.

🏗️ How Will a BAL Rating Affect My Home Design?

Once you receive a BAL rating, your home’s design needs to be updated to reflect the requirements for that level. These adjustments are designed to reduce the likelihood of ignition and structural failure during a bushfire event.

Depending on your BAL, you may need to upgrade things like:

• External wall cladding

• Window frames and glazing

• Door seals

• Vents and eaves

• Roofing materials and gaps

Generally, higher BAL ratings mean more robust construction standards — and a corresponding increase in building costs.

While every site is different, older industry figures give us a rough guide to cost impacts:

• BAL–12.5: may add 3–4% to the base build cost

• BAL–19: roughly 4–5%

• BAL–29: around 6–6.5%

• BAL–40: between 6–10%

• BAL–FZ: potentially 8–10% or more

Of course, these percentages are estimates and can vary based on material choices, location, and builder experience — but they help illustrate why it’s important to factor BAL compliance into your early budgeting.

✅ I’ve Got My BAL Rating — Now What?

Receiving your BAL rating is a milestone — but there are still a few important steps to take before you can start building:

• Update your construction drawings. Your plans must reflect the BAL requirements, including specific upgrades to materials and design details like windows, doors, and roof elements.

• Make sure your builder is on the same page. Not all builders are familiar with AS 3959, so it's important to work with someone who understands what's required.

• Adjust your budget accordingly. If you're in BAL–29 or above, expect meaningful cost implications. Get clear on these before quoting or signing contracts.

• Coordinate all documentation. Before submitting your plans to council or a certifier, ensure everything reflects BAL compliance — this avoids delays and resubmissions.

One of the most common mistakes? Builders quoting off early concept plans that don’t yet include BAL requirements — leading to cost blowouts and construction delays.

👋 Need Help Navigating the Process?

Understanding your BAL rating is the first step in planning a safe and compliant development in a bushfire-prone area. If you're unsure which assessment you need—or what to do once you receive one—our team can help.

We offer site inspections, BAL Assessments, and full Bushfire Management Plans (BMPs) tailored to your development type and location.

Contact us to request a BAL Assessment or get advice on what’s required ➜