Site Preparation

Bushfire (BAL) Ratings Explained

Bushfire-prone areas, the six BAL levels, how an assessment works, and what each rating means for cost.

Reading time

13 min read

Last reviewed

August 2026

Applies to

VIC · NSW · QLD · SA · TAS · WA · ACT

Covers

Bushfire-prone areas · BMO · BAL levels · AS 3959 · Construction requirements

What a BAL actually measures

A Bushfire Attack Level (BAL) is a rating that measures the expected exposure of a building to bushfire attack — ember, radiant heat, flame contact, and burning debris. The BAL is determined by a qualified assessor and sets the construction requirements for the building under Australian Standard AS 3959. The BAL is site-specific: it depends on the vegetation, slope, distance to the cottage, and the Fire Danger Index for the region. A BAL is not a general area rating — it's specific to your building on your site.

Bushfire-prone areas vs the Bushfire Management Overlay

There are two relevant frameworks. A Bushfire Prone Area (BPA) is mapped by each state — if your property is in one, a BAL assessment is required before a building permit. A Bushfire Management Overlay (BMO) is a planning control applied by council to the highest-risk land — it may require a planning permit and a bushfire management statement in addition to the BAL. A property can be in a BPA without being in a BMO, but a BMO property is always within a BPA. Check your state's bushfire-prone area map or your planning property report.

The six BAL levels explained

BAL-Low: insufficient risk to warrant specific construction. BAL-12.5: low risk; ember attack only. BAL-19: moderate risk; ember attack and burning debris. BAL-29: high risk; ember, burning debris, and radiant heat. BAL-40: very high risk; increased radiant heat and flame contact possible. BAL-FZ (Flame Zone): extreme risk; direct flame contact expected. Each step up requires more fire-resistant materials and construction methods, and the cost increases accordingly.

How an assessor determines your BAL

A BAL assessor visits the site (or reviews aerial imagery and site data) and measures the distance and slope to surrounding vegetation, classifies the vegetation type, and applies the AS 3959 method to calculate the BAL. The assessment is documented in a report that is submitted with the building permit application. The BAL must be confirmed before construction — you cannot design for one BAL and build to a lower one. If the vegetation or site conditions change, the assessed BAL may no longer apply.

What each BAL means for construction

Higher BALs require more stringent construction: ember-resistant mesh on subfloors, bushfire-rated shutters or toughened glass, non-combustible or fire-retardant cladding, sealed roof spaces, metal rather than timber verandahs (at higher BALs), and spark-arresting roof vents. At BAL-40 and BAL-FZ, the requirements are substantial and can significantly change the cottage specification and cost. BAL-12.5 adds modest ember-resistant detailing; BAL-29 adds glazing and screening upgrades; BAL-FZ can require a fundamentally different building envelope.

How BAL changes your cost

BAL-12.5 typically adds a modest cost for ember-resistant details. BAL-19 and BAL-29 add progressively more for glazing, screening, and cladding upgrades. BAL-40 and BAL-FZ can add significantly to the cottage price and may require design changes. If your site is in a bushfire-prone area, get the BAL assessment early so the cost is known before you commit. A surprise BAL-40 at the building permit stage can blow a budget that was based on BAL-12.5.

Can you reduce your BAL?

Sometimes. Managing vegetation and increasing the setback from bushfire-prone vegetation can lower the BAL and reduce construction costs. However, some overlays restrict vegetation removal. A BAL assessor can advise on options for your site. Don't clear protected vegetation without checking the planning controls first — the penalties for unauthorised clearing can be significant, and it may not even achieve the BAL reduction you expected if the vegetation is mapped as a vegetation classification that triggers the BMO regardless.

The BAL Assessment & Construction Process

From bushfire-prone area check to compliant construction.

Check bushfire-prone area map
Property in BPA? → BAL assessment
Assessor measures vegetation, slope, distance
BAL level determined (Low to FZ)
Cottage designed to BAL (AS 3959)
Building surveyor approves
Construction to BAL specification

In practice

A cottage in a bushfire-prone area — construction must meet the assessed BAL under AS 3959.
A cottage in a bushfire-prone area — construction must meet the assessed BAL under AS 3959.
Creating defensible space around the building footprint is part of managing bushfire risk.
Creating defensible space around the building footprint is part of managing bushfire risk.

The Six BAL Levels at a Glance

What each level means for risk, construction, and cost.

BALRisk levelAttack typeCost impact
BAL-LowInsufficientNone specificNone
BAL-12.5LowEmbersModest
BAL-19ModerateEmbers + debrisModerate
BAL-29HighEmbers + debris + heatSignificant
BAL-40Very highHeat + flame contactHigh
BAL-FZExtremeDirect flameVery high

From our experience

From our experience, the BAL is the site condition that most often surprises customers — not because it's hidden, but because it's not checked early. A property that looks like a normal rural block can be in a bushfire-prone area with a BAL-29 or higher, which materially changes the cottage specification and cost.

We've had customers budget for BAL-12.5 and discover BAL-40 at the assessment stage. The difference in construction cost was tens of thousands of dollars. A $500 assessment at the start would have caught it before the budget was set.

Common Mistakes to Avoid

  1. 1

    Not checking the bushfire-prone area map before committing, then discovering a BAL is required at permit stage.

  2. 2

    Assuming a low BAL when the site is near dense vegetation — the assessed BAL can be much higher.

  3. 3

    Designing the cottage before the BAL assessment, then needing costly specification changes.

  4. 4

    Clearing vegetation to reduce BAL without checking the Vegetation Protection Overlay — unauthorised clearing is an offence.

  5. 5

    Assuming BAL-12.5 and BAL-40 are similar — the cost and construction difference is substantial.

  6. 6

    Not getting the BAL assessment in writing — the building surveyor needs a formal report.

  7. 7

    Assuming the BAL won't change — if vegetation grows back, the assessed BAL may no longer apply.

  8. 8

    Treating a BPA and a BMO as the same thing — a BMO may require a planning permit in addition to the BAL.

What changes between states?

Requirements vary by jurisdiction — always confirm with your local authority.

StateNotes
VictoriaBushfire-prone areas mapped by the CFA. BMO is a planning control under the Victoria Planning Provisions.
NSWBushfire-prone land mapped by the NSW RFS. Planning for Bushfire Protection (PBP) guide applies.
QueenslandBushfire-prone areas mapped by the QFD. AS 3959 applies for construction.
SA / TAS / WAEach state maps bushfire-prone areas and adopts AS 3959 for construction. Check your state fire authority's map.

When this guide doesn't apply

This guide may not apply if:

  • Your property is not in a mapped bushfire-prone area — a BAL assessment may not be required (confirm with your building surveyor).
  • You're building in a fully urban, fire-protected environment with no vegetation exposure.
  • You're building outside Australia — bushfire construction standards differ by country.

Frequently Asked Questions

Can I build a cottage in a bushfire zone?

Yes, in most cases, but the cottage must meet the BAL assessed for the site. A high BAL may restrict some materials and add cost. A BMO may also require a planning permit. A BAL assessment early in the process tells you what's involved.

What is the difference between BAL-12.5 and BAL-40?

BAL-12.5 means ember attack only and requires modest fire-resistant detailing. BAL-40 means very high radiant heat and possible flame contact, requiring substantially more fire-resistant materials and construction. The cost difference between them can be significant.

Who can do a BAL assessment?

A BAL assessment must be done by a qualified assessor — often a building designer, planner, or specialist bushfire consultant accredited to assess to AS 3959. The report is submitted with your building permit application.

Does a high BAL mean I can't build?

No. You can build at any BAL up to BAL-FZ, but higher BALs require more fire-resistant construction and add cost. Very high BALs may make some designs impractical, but they don't prohibit building outright.

Can I reduce my BAL by clearing vegetation?

Sometimes, but check the planning controls first. Some overlays restrict vegetation removal, and unauthorised clearing is an offence. A BAL assessor can advise on what clearing is permitted and whether it would reduce your BAL.

Authoritative sources & further reading

Standards Australia — AS 3959 (bushfire construction)CFA Victoria — bushfire-prone areasVictorian Planning — Bushfire Management OverlayNSW RFS — bushfire-prone landNCC — bushfire construction

BAL Assessment Checklist

A checklist for preparing for your BAL assessment — the information to gather, the vegetation and slope factors that affect your rating, and the construction cost implications of each BAL level, so you understand your result before you commit.

This page provides general information about the pathway commonly followed in Victoria. Requirements vary by property, local government area, building classification and proposed use. Obtain site-specific advice before making financial commitments.

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Reviewed by

Homes & Domes Victoria Technical Team

Last technical review

August 2026

Sources updated

August 2026

All Learning Centre guides

Last reviewed: July 2026 · Applicable jurisdiction: Victoria · General information only — not legal, planning or engineering advice.

Requirements vary by property, local government area, building classification and proposed use. Obtain site-specific advice before making financial commitments.