A roof truss is the structural framework that supports your roof. It sits on top of the walls, carries the weight of roofing materials, and transfers that load safely down into the building’s foundations. Without trusses, roofs simply wouldn’t hold.
In Australia, timber has traditionally been the go-to material for roof trusses. It’s familiar, widely available, and easy for builders to work with. But in recent years, steel roof trusses have become increasingly popular, particularly in commercial construction, multi-residential developments, bushfire zones, and termite-prone areas.
While both systems do the same job, they perform very differently.
What Are Steel Roof Trusses?
Steel roof trusses are engineered structural frames made from lightweight, high-tensile galvanised steel. They are designed using specialised software, precision-cut in a factory, and delivered to site as pre-assembled units.
Each truss is:
- Computer-designed for exact load requirements
- Manufactured from galvanised steel (commonly G550 grade)
- Pre-labelled and delivered ready for installation
Because they are factory-made, steel trusses offer a high level of accuracy and consistency across the entire structure.
How Timber Roof Trusses Are Made
Timber trusses are also prefabricated but use treated softwood, typically pine. The components are cut and joined using metal connector plates pressed into place.
Timber trusses are designed in accordance with Australian standards such as:
- AS 1684 (Residential Timber Framing Code)
- AS 4440 (Installation of Nail-Plated Timber Trusses)
Unlike steel, timber is a natural material, meaning:
- It can vary in moisture content and density
- It may expand, shrink, or warp over time
- No two pieces are exactly identical
Steel Roof Trusses vs Timber Trusses: Key Differences
1. Strength and Span Capability
Steel roof trusses offer significantly higher tensile strength than timber. This allows:
- Longer spans without internal support
- Fewer load-bearing walls
- More open-plan design flexibility
Timber works well for standard residential spans but has limitations for larger or complex structures.
2. Dimensional Stability
One of the biggest advantages of steel roof trusses is stability.
Steel:
- Does not shrink or expand
- Does not warp, twist, or bow
- Maintains exact alignment over time
Timber:
- Can move with moisture and temperature changes
- May cause ceiling cracks or misalignment over time
3. Termite Resistance
Steel is completely termite-proof.
In termite-prone areas of Australia, this is a major advantage. Timber trusses require chemical treatment and ongoing risk management, while steel eliminates the issue entirely.
4. Fire Performance
Steel is non-combustible and does not burn.
In bushfire-prone regions, steel roof trusses are often preferred because they:
- Meet strict bushfire construction requirements
- Do not contribute to fire spread
- Maintain structural integrity at high temperatures
5. Cost Considerations
Timber trusses are generally more cost-effective upfront.
Timber = lower initial material cost
Steel = higher upfront cost but reduced long-term risk
However, steel may save money in high-risk environments by reducing maintenance, repairs, and pest-related damage.
6. Installation Process
Steel trusses are:
- Precision manufactured
- Delivered pre-labelled
- Typically craned into position
- Installed using bolts and brackets
Timber trusses:
- Can be easier to modify on-site
- Require less specialised tooling
- Are familiar to most residential builders
Steel installation is faster in large-scale projects, while timber offers more flexibility on smaller builds.
7. Thermal and Acoustic Performance
Timber naturally performs better in:
- Sound absorption
- Thermal insulation (less heat conduction than steel)
Steel may require additional insulation detailing to prevent thermal bridging.
Where Steel Roof Trusses Are Best Used
Steel roof trusses are ideal for:
- Wide-span buildings
- Commercial and industrial projects
- Multi-dwelling developments
- Bushfire-prone areas
- Termite-risk regions
- Architecturally complex roof designs
Where Timber Roof Trusses Are Best Used
Timber remains a strong choice for:
- Standard residential homes
- Budget-conscious builds
- Renovations and extensions
- Projects requiring on-site modifications
- Builders experienced primarily in timber framing
Lifespan: Steel vs Timber Roof Trusses
Both systems can last 50+ years when installed correctly.
Timber:
- Long lifespan if protected from termites and moisture
- Vulnerable to rot, pests, and humidity issues
Steel roof trusses:
- Resistant to termites, rot, and warping
- Long-lasting galvanised protection
- Performs well in most Australian environments
In coastal areas, enhanced galvanising may be required due to salt exposure.
Final Verdict: Which One Should You Choose?
There is no one-size-fits-all answer.
Choose timber trusses if:
- You’re building a standard home
- Budget is the main priority
- There are no major termite or bushfire risks
Choose steel roof trusses if:
- You need long spans or open-plan designs
- You are building in termite or bushfire zones
- You want long-term dimensional stability
- You are working on multi-unit or commercial projects
Conclusion
Steel roof trusses are not about replacing timber entirely they are about offering a stronger, more stable alternative for specific conditions.
Both systems are proven, engineered, and widely used across Australia. The right choice depends on your site conditions, design requirements, and long-term performance expectations.
If in doubt, always consult a qualified builder or structural engineer before deciding.