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Steel Roof Trusses

Steel roof trusses form the overhead structural framework of a building, designed to support roofing materials while distributing weight evenly to the walls below. Engineered for high strength-to-weight ratio, they allow for longer spans without internal load-bearing walls, creating openc and flexible spaces beneath.

What Are Steel Trusses and Why Use Them?

Steel trusses are engineered roof structures made from light‑gauge galvanised steel, featuring triangular web configurations that deliver superior strength-to-weight ratio and unmatched design flexibility.

They’re commonly used in both residential and commercial applications, capable of spanning up to 19 m clear widths without internal supports, ideal for open-plan layouts or industrial sheds.

These trusses often arrive pre-cut, straight, and true, eliminating on-site bending or twisting. Builders report faster assembly, minimal waste, and fewer finishing issues.

Steel Trusses vs Timber Roof Truss: Performance Comparison

When comparing steel trusses to a timber roof truss, the performance benefits become clear. Steel trusses are approximately 40% lighter than equivalent timber trusses, which significantly reduces manual handling risk and installation labour.

Timber, while widely used, is susceptible to pests, moisture, and fire, whereas steel resists all these factors and provides better long-term dimensional stability. Though steel may involve a higher upfront cost, its longevity, minimal maintenance needs, and precision in installation often deliver better value, especially for larger builds

Designing With Steel Frame Trusses: What Builders Must Consider

Designing with steel frame trusses requires detailed CAD or BIM modelling to ensure correct pitch, span, and load capacity. Web configurations are engineered to distribute roof and live loads efficiently across both top and bottom chords, with pre-punched service holes to accommodate wiring, insulation, or ceiling mounts.

Premium steel like BlueScope TRUECORE® ensures compliance with AS 4100 and AS/NZS 4600 standards, often backed by 50-year warranties.

Builders must also verify wind ratings per AS/NZS 1170.2, ensuring truss specifications align with the project’s location and design requirements.

Beams for Roof Support: Steel Trusses and Roof Beams Together

A well-designed beam for roof support integrates with a truss system to handle structural loads. The top and bottom chords transfer weight horizontally, while web members transmit forces vertically to the external wall frames.

This system maximizes open-plan layouts by eliminating internal load-bearing walls. Some systems, like Spantec’s Boxspan, offer high torsional stiffness in span lengths over 12 m, improving precision and reducing assembly complexity

How Far Apart Are Roof Trusses?

Determining roof truss spacing is a critical decision in steel truss design and installation. In Australia, builders typically follow spacing guidelines between 600 mm and 900 mm centre-to-centre for standard residential steel roof trusses supporting metal roofing or battens.

This range balances structural support with material efficiency. In low wind zones (up to N3), sheet-metal roofing systems may allow spacing up to 1,200 mm, if specified by a certified truss fabricator and aligned with NCC provisions.

The choice of spacing depends on several key factors:

Roof Sheeting Weight and Type: Lightweight roof sheeting such as corrugated or concealed-fastener profiles may permit wider spacing, while heavier concrete or tile roofs require closer support, typically around 600 mm or less.
Roof Span and Pitch: Longer spans or flatter roof pitches (≤15°) often require tighter spacing to ensure stiffness and prevent deflection under load.
Wind Zone Classification: Designs in high wind zones (C2, C3) or cyclone-prone regions often use tighter spacing and include additional bracing in between trusses, as per AS/NZS 1170.2 guidelines.

Skillion Roof Framing Using Steel Trusses

When building a skillion roof framing system, commonly seen in modern homes and sheds, steel trusses offer unmatched adaptability. They can be custom-fabricated to fit shallow pitches or mono-sloped designs without the need for intricate timber joinery.

Curved and vaulted profiles are also achievable, expanding architectural possibilities.

Installing Trusses for Roof: Step‑by‑Step Guide

1. Preparation & Layout
Confirm your engineered truss layout and ensure wall plates are level and stable. All loads, like solar panels or HVAC, must be accounted for in the design before ordering.

2. Receiving & Storing Trusses
Inspect trusses on delivery for damage and store them flat on supports spaced every ~3 m to prevent sagging. Avoid exposure to direct sun or moisture.

3. Marking Truss Centres
Mark the truss centrelines on the top plate using chalk or laser. Typical spacing is 600–900 mm, unless certified for up to 1,200 mm.

4. Erecting & Aligning Trusses
Use a crane with spreader bars (for spans over 9 m). Lift from panel points, not the apex. Carefully align each truss plumb and square before fixing.

5. Fixing to Wall Plates
Secure each truss using approved brackets (e.g. TrussLok screws), ensuring at least four fixings per connection to resist wind uplift.

6. Temporary Bracing
Immediately brace the first truss securely to ground or a rigid structure. Install top-chord ties every 3 m and bottom-chord ties every 4 m using timber (25×50 F5 or TrussSpacers up to 900 mm centres; 35×70 F5 for 900–1,200 mm).

7. Permanent Bracing
Once temporary restraint is in place, install permanent cross-bracing, web ties, ceiling binders, and diagonal straps in accordance with The Guide or NASH booklets.

8. Spacing & Alignment Check
Verify spacing does not exceed design specs. Use a string line or laser to ensure consistent alignment. Tolerances: no more than L/200 or 50 mm bow/tilt in truss orientation.

9. Fixing Battens & Sheeting
Do not install battens or roof sheeting until permanent bracing is complete. Attach battens at web node points and install insulation if required before sheet fixing begins.

10. Final Inspection & Safety
Before trades move on or roof is loaded, confirm all fixings, bracing, and alignment. Use checklists from MiTek or trusted suppliers. Ensure site safety measures, fall prevention protocols, and proper PPE compliance

For complete instructions, safety protocols, load tables, and design guidelines, refer to the MiTek Guide for Roof Truss Installation and the AS 4440 Australian Standard for installation of prefabricated roof trusses.

So Why Choose Steel Trusses?

Builders choose steel trusses for their combination of performance and practicality: they deliver long clear spans with minimised weight, resist pests, moisture, and fire, and support faster and more accurate installation. The consistency of steel means fewer callbacks and easier cladding fit-out. Better yet, steel trusses are renewable and recyclable, supporting sustainable, long-term value installations.

Packaged as part of integrated steel frames & trusses, they boost build coordination, reduce site conflicts, and streamline project timelines.

Looking for Steel Trusses Near You?

If you’re building in Melbourne or regional Victoria and searching for reliable steel trusses, ISG Frames offers precision-engineered steel roof trusses and fully integrated steel frames & trusses packages.

We specialise in integrated wall, floor, and roof solutions, designed for compliance, prefabrication accuracy, and efficient onsite assembly.

Explore our project gallery and discover why builders rely on ISG Frames for quality, trust, and seamless coordination throughout their builds

FAQs

Can steel trusses improve acoustic and thermal performance?

Yes, with proper detailing, metal roof trusses can enhance both sound insulation and thermal comfort. Steel truss assemblies with insulated roofing and acoustic pads can deliver reduction of sound transmission up to ~45–55 dB in residential applications. Light-steel framing systems easily incorporate thermal breaks or insulation layers to minimize thermal bridging, improving energy efficiency in line with modern building standards

Are there span limits or common truss types?

Steel trusses come in standard configurations such as Pratt, Howe, or scissor trusses tailored for different spans and roof types. Common span ranges extend up to 20 m or more, depending on truss type and load. The geometric design minimizes material use while delivering high load capacity and rigidity, ideal for residential thru to large-scale industrial roofs

What are the main drawbacks of steel trusses, and how can they be addressed?

While steel frame trusses offer many benefits, they pose some challenges:

Steel conducts heat more than timber, raising condensation or thermal bridging risks
They’re prone to corrosion in harsh environments if not properly coated
Installation needs precise alignment and skilled labor

These can be mitigated by using thermal breaks, quality galvanized or epoxy coatings, and involving experienced installers familiar with truss bracing guidelines and NCC tolerance requirements