Building in bushfire-prone areas presents unique challenges, particularly when selecting the right materials. In many areas of Australia, new buildings and extensions to existing buildings require assessment for their potential exposure to bushfires. This article explores how Wesbeam’s LVL is suitable for construction in these areas, highlighting its properties and compliance with safety standards.
Australian Standards for Construction in Bushfire Prone Areas
Australian Standard AS 3959-2018 Construction of buildings in bushfire-prone areas is the primarily referenced document in the National Construction Code 2022. This standard was created through a collaborative process involving experts. It prioritises transparency and balanced representation to ensure the highest level of safety and durability in these high-risk regions.
What Are We Designing Against?
Designing against bushfires requires minimising the risk of ember attacks and radiant heat.
Ember Attacks:
Ember Attacks are the most common cause of property damage or destruction from bushfires. These small, burning pieces of debris can travel hundreds of metres ahead of the main firefront. They can easily slip through gaps in your home, such as open windows, doors, or cracks in the walls. The minimum firebreak width is typically 10-20 metres to combat ember attacks (based on DFES recommendations).
Radiant Heat:
Bushfires also release intense heat energy, known as radiant heat. The heat spreads from the firefront rapidly weakens as it travels further. Even without direct flames or embers, radiant heat can pose serious risks. High levels of radiant heat can cause combustible materials inside a building to ignite.
Residents do not have to be located in remote bushland to be identified as a bushfire-prone area. Areas adjacent to parks, native shrubs, reserves and even dunes can be considered bushfire-prone areas.
What is a Bushfire Attack Level (BAL)?
The construction requirements for your home will depend on its Bushfire Attack Level (BAL). This is a measure of the heat given off by a bushfire at the closest lot of vegetation where a bushfire is likely to occur. To determine the BAL, experts carry out a site inspection at the beginning of the design stage. An accredited BAL assessor will typically conduct this assessment.
BAL zones range from BAL-LOW through to BAL-FZ or “Flame Zone”. The numbers in between are a measure of the radiant heat expected. For example, BAL-12.5 means the risk of radiant heat is considered low, while BAL-40 means the risk is high.
In most cases, the closer a property will be to flames, the higher its BAL. However, there are other factors in assessing a site’s BAL including the land's slope, surrounding vegetation, and nearby buildings. With each level of increase, the requirements for the home's construction will also increase, as will the associated costs.
At What BAL can Wesbeam LVL be used?
Wesbeam LVL and e-joists can be used in any BAL construction without restriction. There are no restrictions on the use of timber in framing and internal applications, provided that the requirements of AS 3959 and the National Construction Code are met. Wesbeam’s wide range of LVL products can be used in roof, wall, floor and formwork applications for both residential and commercial buildings.
However, there are different requirements for protecting the structural timber using different systems depending on the BAL. For anything up to BAL-19, all Wesbeam products can be used as per their normal applications. There are additional requirements for anything above this level, like lining the underside of the floors with fibre cement sheeting.
The table below lists the construction requirements for each bushfire attack level as per AS 3959-2018:
| Building Element | BAL–LOW | BAL–12.5 | BAL–19 | BAL–29 | BAL–40 | BAL–FZ |
|---|
| Roof | Framing members | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Walls (external and internal) | Framing members | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Floors (bearers, joists) | Enclosed¹ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Unenclosed² | ✓ | ✓ | ✓ | ✓ | ✓
(With framing members lined on the underside with fibre-cement sheeting) | ✓
(With framing members lined on the underside with 1 x 16 mm fire-grade plasterboard) |
| Veranda, carport and awning roofs | Framing members – Forming part of the main roof space | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Framing members – Separated from the main roof space by a compliant wall | ✓ | ✓ | ✓ | ✓
(With rafters lined on the underside with minimum 6mm fibre-cement sheeting) | ✓
(With rafters lined on the underside with minimum 6mm fibre-cement sheeting) | ✓
(With rafters lined on the underside with minimum 6mm fibre-cement sheeting) |
Framing for:
decks, steps, ramps and landings | Enclosed¹ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Unenclosed² | ✓ | ✓ | ✓ | ✓
Bushfire-resisting timber or System complying with AS 1530.8.1 | ✓
System complying with AS 1530.8.1 | ✓
System complying with AS 1530.8.2 |
✓: All Wesbeam LVL products.
1: Wall enclosing sub-floor space to be of the same construction as for external walls - refer to AS 3959.
2: Floor bearers and joist minimum 400mm above finished ground level.
Note: Some states have special rules that must be checked in the National Construction Code.
Wesbeam LVL provides a sustainable and practical solution for building in bushfire-prone areas. When combined with a range of prevention strategies, LVL can reduce the risk of ember and radiant heat damage from fires.
For more information on our treated timber and LVL products, contact us today or speak to our technical experts on e-chat.