What is BAL29 and Do You Need Fire Retardant Treatment on Your Timber?

If you're building, renovating, or buying property in a bushfire-prone area, you've probably encountered the term "BAL29." But what does it actually mean? And does it require you to treat your timber?

Understanding Bushfire Attack Levels

BAL stands for Bushfire Attack Level. It's a system defined by AS3959 (the Australian Standard for construction in bushfire-prone areas) that rates the potential exposure of a building to ember attack, radiant heat, and direct flame contact.

The BAL system has six categories:

• BAL-LOW: Minimal risk — no specific construction requirements
• BAL-12.5: Ember attack and radiant heat up to 12.5 kW/m²
• BAL-19: Radiant heat up to 19 kW/m² — increased construction requirements
• BAL-29: Radiant heat up to 29 kW/m² — significant construction requirements
• BAL-40: Very high radiant heat — extensive construction requirements
• BAL-FZ: Flame Zone — direct flame contact expected

Your property's BAL rating is determined by factors including distance to vegetation, slope of the land, and local fire weather conditions. Your local council assigns the rating based on these factors.

What Does BAL29 Require?

BAL29 is where construction requirements become significantly more demanding. Buildings in BAL29 zones must withstand higher radiant heat loads and are at greater risk of ember ignition.

For timber specifically, AS3959 requires:

• External timber must be bushfire-resisting timber (specific species or treated timber)
• Decking must be either bushfire-resisting timber or non-combustible
• All exposed timber must meet minimum thickness requirements
• Gaps between boards must be limited or covered with ember guards

For many common timber species, meeting BAL29 requirements means either using specific naturally resistant species (like some hardwoods) or treating the timber with an approved fire retardant.

Who Needs BAL29 Treatment?

If you're building new or renovating in a BAL29 zone, you'll need compliant timber for:

• External cladding and fascia
• Decking and outdoor structures
• Exposed structural elements
• Fencing within the building envelope
• Carports and pergolas attached to the dwelling

Even if you're not required to meet BAL standards (for example, if you're not building new), treating timber can still make sense for fire protection — especially in high-risk areas.

Penetrating Liquid vs Intumescent Paint

There are two main types of timber fire treatment:

Penetrating Liquid Fire Retardants:These soak into the timber fibres, creating protection from within. They're typically clear, accept standard finishes (stain, paint, oil), and don't change the appearance of the wood. KillFlame Timber is a penetrating liquid.

Intumescent Paints:These sit on the surface and expand when heated, forming an insulating char layer. They're effective but change the appearance of the timber and can chip or wear over time.

For most construction applications, penetrating liquid treatments are preferred because they integrate with the timber rather than coating it.

How to Apply Penetrating Fire Retardant

For KillFlame Timber:

1. Timber must be raw, clean, and dry (moisture content below 20%)
2. Remove any existing finishes — the retardant must penetrate
3. Apply liberally by spray, brush, or dip
4. Allow to penetrate and dry completely (12-24 hours)
5. Apply topcoats after full cure

Coverage is approximately 7m² per litre, depending on timber porosity. Softwoods absorb more than hardwoods.

Documentation and Certification

When building in a BAL zone, you'll need to demonstrate compliance to your building certifier. This typically means providing:

• Product data sheets showing BAL rating
• Evidence of correct application (photos, signed declaration)
• Test certificates from accredited laboratories

Keep these records — they may be required for future insurance claims or property sales.

Making the Right Choice

If you're building in a BAL29 zone and want to use standard timber species, fire retardant treatment is likely your most practical option. It allows you to use familiar materials while meeting compliance requirements.

Choose a product that's specifically rated for BAL29 applications and — importantly — one that's PFAS-free. Your timber will be exposed to rain, soil, and waterways. The last thing you want is to introduce forever chemicals into your environment.