Bushfire Resistant Timber Cladding: What You Need to Know

Here’s a question we hear regularly from architects and builders: Can I still use timber cladding in a bushfire zone?

It’s a fair concern. According to the Climate Council, bushfire conditions across Australia are now significantly worse than in previous decades. Communities that never considered themselves at risk are reassessing. And when the stakes are this high, the instinct is to rule out anything combustible.

But here’s what most people get wrong about timber and bushfire. The Australian Standard doesn’t ask whether a material burns. It asks how it performs — at what temperature, at what rate, within what system. And under AS 3959, timber cladding can absolutely be specified in bushfire-prone areas, including higher-risk zones, when the right species and detailing are used.

That’s the distinction this guide is built around. Not whether timber belongs in bushfire areas, but how to specify it properly — which species meet the density thresholds, what the BAL levels actually require, and where Mortlock Timber’s cladding systems fit within those requirements.

What does “bushfire-resistant” actually mean?

Let’s clear up a common misconception first. Bushfire-resistant timber cladding doesn’t mean fireproof timber. No timber is fireproof.

What it means is that certain species, when installed within a compliant wall system and detailed correctly, can meet the performance requirements of AS 3959 (Construction of buildings in bushfire-prone areas) for a given BAL classification.

It’s a system-level question, not just a material one. The same species might pass at one BAL level and fall short at another. What matters is how these factors work together:

• The BAL rating assigned to the site
• The density of the timber species
• Minimum board thickness
• Fixing and junction detailing
• How the cladding integrates with the wall assembly behind it

Get the system right and timber works. Get one element wrong, and it doesn’t — regardless of how dense the species is.

It all starts with a site assessment

Every bushfire-prone project starts the same way: with a site assessment. Before you choose a single material, you need to know your Bushfire Attack Level.

The BAL determines what the building needs to withstand — radiant heat, ember attack, or direct flame contact. Everything that follows, from material selection to junction detailing, is shaped by that rating.

BAL ratings, explained

BAL stands for Bushfire Attack Level. It measures how severely a building could be exposed to ember attack, radiant heat and direct flame contact, expressed in kilowatts per square metre (kW/m²).

You’ll need an accredited BAL assessor to determine the level for your site. Once that’s established, your plans, material specs and construction methods all need to align with the requirements for that level.

The governing document is AS 3959–2018. If you want the deep technical detail, the Wood Solutions Building with Timber in Bushfire-prone Areas Technical Design Guide is one of the most comprehensive references available for architects, designers and builders.

The six BAL levels at a glance

There are six BAL classifications, ranging from negligible risk through to direct flame exposure. Here’s what each one means in practice.

(Based on Appendix G of AS 3959, sourced from Wood Solutions Guide #04.)

Each step up tightens what you can specify. Materials, junctions, glazing, insulation — it all needs to meet the relevant provisions of AS 3959.

Why timber doesn’t deserve to be ruled out

This is where most assumptions fall apart. People hear “bushfire zone” and immediately cross timber off the list. But that’s not how AS 3959 works.

The standard doesn’t ban combustible materials outright. It sets performance benchmarks. And high-density hardwoods meet those benchmarks in ways that matter: they ignite more slowly, they burn at a predictable rate, and that predictability is something engineers can design around.

We’ve worked with architects on projects from coastal NSW to regional Victoria, where timber was the preferred façade material, and the site was rated BAL–29. In each case, the answer wasn’t to abandon timber — it was to select the right species, pair it with the right system, and detail it correctly.

Timber can form part of a compliant façade solution in BAL–12.5, BAL–19 and BAL–29 areas. The question isn’t if — it’s how.

Why density is the deciding factor

Why does species density matter so much? Because denser timber takes longer to ignite and burns more slowly under radiant heat. That’s the physical property AS 3959 uses to set its thresholds.

The numbers are straightforward:

• BAL–19: Minimum timber density of 680 kg/m³
• BAL–29: Minimum timber density of 750 kg/m³ at 12% moisture content

But density alone won’t get you across the line. Board thickness, fixing methods, cavity treatment and junction detailing all factor into compliance. A species that meets the density threshold can still fail if the installation doesn’t stack up.

This is why we encourage specifiers to lock in both the species and the system early. It avoids late-stage surprises when the certifier reviews the documentation.

Which species resist fire best?

Not all timber burns the same way. Higher-density species resist ignition longer and burn more predictably — two properties that make a real difference in bushfire design.

Common fire-resistant species include:

• Pacific Teak
• Spotted Gum
• Ironbark
• Blackbutt
• Irongum

That said, fire-resistant doesn’t mean universally compliant. Each species needs to meet the density threshold for the specific BAL level. The next section breaks that down.

Matching species to BAL levels

Here’s the practical breakdown. Which species you can specify depends entirely on your BAL classification:

Notice how the list narrows as BAL increases. By BAL–29, you’re down to three species. At BAL–40 and BAL–FZ, timber is off the table entirely — those levels require non-combustible materials due to direct flame risk.

Note: Jarrah has been removed from the species lists pending confirmation that it meets the relevant AS 3959 thresholds. The original blog included Jarrah in the BAL–LOW through BAL–19 lists. Reinstate once verified.

What BAL level can Mortlock help you reach?

We can take you up to BAL–29. The three species we offer that meet that threshold are spotted gum, blackbutt and ironbark.

These fall under the external walls (Section 5.4) and decking (Section 6.73.3) provisions of AS 3959:2018. The standard requires species listed in Table E1, Appendix E, and all three qualify.

A quick note on how BAL compliance cascades: if your system is compliant at BAL–29, it automatically meets requirements for BAL–19, BAL–12.5 and BAL–LOW. So specifying to the higher level gives you coverage across the board.

We don’t offer products rated for BAL–FZ. That classification requires non-combustible materials — the risk from direct flame contact and radiant heat above 40 kW/m² puts it beyond what any timber can achieve.

How the profile and fixing design affect compliance

Species selection is the primary factor when specifying timber cladding in bushfire-prone areas. Under AS 3959, Density is a key factor under the deemed-to-satisfy pathway, and the inherent density of the timber determines its suitability for different Bushfire Attack Levels (BAL). The way timber cladding is built, fixed, or joined does not change or improve the BAL rating of the timber itself.

However, while the timber’s rating is based on density alone, the overall wall system still must be designed to withstand ember attack. Think about it from an ember’s perspective. Embers find their way through gaps, into cavities, behind junctions. A bushfire-compliant façade needs to shut those pathways down. That means tight joint configurations, compliant cavity barriers, and concealed fixing systems that don’t leave the cladding exposed at connection points.

It is a common misconception that board thickness plays a role in the BAL rating of timber cladding.While there are strict minimum thickness requirements for other building elements in higher BAL zones—such as requiring solid timber doors to be at least 35mm thick—this has nothing to do with timber cladding. For cladding, compliance is strictly based on the density of the chosen timber species. AS 3959 does include minimum requirements in some assemblies and test conditions.

The earlier you coordinate species, profile and installation method, the smoother the path to compliance. We’ve seen projects hit roadblocks late in documentation simply because the profile wasn’t considered alongside the species from the start.

It’s worth noting that fire-retardant chemical treatments exist for timber, but they’re separate from the species-based compliance pathway under AS 3959. The density thresholds in the standard are based on the natural properties of the timber itself. Mortlock’s approach is to specify species that meet those thresholds without relying on applied treatments — spotted gum, blackbutt and ironbark achieve BAL–29 compliance based on their inherent density.

Mortlock products built for bushfire zones

We’ve been supplying cladding for bushfire-rated projects for over a decade — working alongside architects and builders from initial specification through to installation sign-off.

Two of our product lines are suitable for bushfire-rated areas:

• Trendplank Timber Cladding: Our concealed fixed system for external walls, ceilings and internal feature walls. The profile is designed to accommodate natural timber movement while maintaining tight, consistent joints. Available in spotted gum, blackbutt and ironbark for BAL-rated applications up to BAL–29.
• Shou Sugi Ban Timber Cladding: Charred timber cladding manufactured in-house at Mortlock. The carbon-black finish is striking, and the charring process reduces ongoing maintenance. Available in Irongum or spotted gum. Achieves BAL–29 when spotted gum is specified.

Does charring increase the fire rating?

A question we get asked a lot. The short answer is no. We’ve had this lab-tested. Charring the surface doesn’t change the fire properties of the underlying timber. The BAL compliance of our Shou Sugi Ban range comes from the species density, not the charred finish.

Keeping timber in the design brief

A BAL rating doesn’t have to mean abandoning the material palette you want. It means being more deliberate about how you use it.

We regularly work with architects who come to us early in the design phase — sometimes before the BAL assessment is even finalised — to understand what’s possible. That early conversation makes a difference. It means the species, profile and detailing are considered together from the start, rather than retrofitted after the fact.

Timber cladding can remain part of the design approach in BAL–12.5, BAL–19 and BAL–29 zones. It’s not a compromise. It’s an informed specification.

Talk to us about your project

If you’re working on a bushfire-rated project and want to use timber, we can help you work through the species and system options for your BAL level. We review density thresholds, installation requirements and detailing considerations as part of the specification process.

Speak with our team on 1800 058 420 or enquire via our website. For product specifications and pricing, download our Pricing and Product Guide.