Roof Trusses Guide | Types, Design & Installation

Roof trusses provide efficient, engineered framing for Australian homes and commercial buildings. Manufactured under controlled conditions, trusses deliver speed, consistency and predictable performance—when designed and installed to Australian Standards.

Trusses vs Conventional Framing

Trusses are engineered assemblies using top/bottom chords and webs to transfer loads efficiently. Compared to stick-framing, trusses enable longer spans, faster installation and reduced material waste.

Types of Roof Trusses

Common (Fink) truss
King and Queen post trusses
Howe and Pratt trusses
Attic (room-in-roof) trusses
Scissor, Mono, Gable-end, Hip and Girder trusses

Components

Top chord (compression), Bottom chord (tension)
Web members forming efficient triangles
Heel, Peak, and Gusset plates (connector plates)

Materials

Timber trusses dominate housing (treated pine, engineered wood). Steel trusses appear in commercial/long-span applications. Selection depends on span, loads, exposure and budget.

Design Principles and Standards

Loads include dead, live, wind and (in alpine areas) snow. Design must comply with AS 1684 (Residential timber-framed construction) and AS 4055 (Wind loads). Truss spacing and bracing are specified by the truss engineer.

Load Example (described)

Example span 9.0 m, roof pitch 25°, N3 wind classification. Engineer specifies web configuration, plate sizes and bracing schedule accordingly.

Manufacturing and Quality

Computer-aided design and jig fabrication ensure accuracy. QA checks include plate embedment, chord straightness and member grade.

Installation

Site access and storage on level supports
Crane lift according to lift points; avoid bending
Setting trusses to plan, fixing to top plates
Temporary bracing during erection
Permanent bracing, tie-downs, and connections per engineer

Safety

Edge protection, fall arrest systems and exclusion zones for lifts are mandatory on active sites.

Costs

Timber trusses: $180–$400 per truss (size and complexity dependent)
Steel trusses: +20–40% over timber for similar spans
Design/engineering: $1,200–$3,500 typical for housing
Installation: $35–$65/m² of roof area

Advantages and Limitations

Speed, consistency, long spans, cost-effectiveness
Limited modification on site; attic space constraints for some profiles

Common Issues and Solutions

Truss uplift—allow for flexible ceiling fixings
Bracing omissions—use installation checklists
Poor connections—verify nail plate seating and tie-downs

Case Studies

Residential hip roof, Hills District: Prefabricated timber trusses reduced erection time from 7 to 2 days.

Community hall, Central Coast: Steel girder trusses enabled 18 m clear span with minimal internal supports.

Conclusion

Engage certified truss designers and installers, follow AS 1684/AS 4055 and the manufacturer's installation manuals, and verify bracing and tie-downs for a safe, durable roof structure.