Truss vs. Rafter Framing: A Structural Review for Ontario

Choosing the appropriate roof framing system is an important step in wood-frame construction across Ontario. Roof behaviour directly influences how gravity and lateral loads are transferred, how the structure deflects over time, and how reliable the building remains under seasonal snow and wind conditions.

Both roof trusses and traditional rafter systems are well-established methods, but their engineering performance, installation requirements, and long-term serviceability differ—especially when evaluated under Ontario Building Code (OBC) provisions.

What Are Truss Roofs?

A roof truss is a prefabricated structural unit composed of top chords, bottom chords, and web members arranged in a triangulated configuration to efficiently transfer loads.Key engineering characteristics:

• Manufactured using engineered calculations to ensure predictable performance

• Reduced onsite variability and improved geometry control

• Ideal for long spans and complex roof profiles

• Available as wooden roof trusses and steel roof trusses

• Efficient for open-concept plans due to reduced need for interior bearing walls

Because trusses follow well-defined structural idealizations, they provide high reliability in Ontario climates.

Structural Principles of Prefabricated Truss Systems

In truss roof framing, the triangular configuration distributes loads through multiple members, minimizing bending demand and reducing stress concentrations.

Structural benefits include:

• Uniform transfer of gravity and lateral loads

• Lower susceptibility to creep, sagging, and seasonal movement

• Consistent roof truss spacing and improved stiffness

• Better performance under Ontario snow loads and wind effects

• Compatibility with modern insulation and roof sheathing systems

This predictable behaviour is one reason engineered roof trusses are widely preferred in residential structural engineering.

Material Efficiency and Project Cost Implications

From a structural and project-management perspective, prefabricated roof trusses offer:

• Reduced site labour and installation time

• Optimized material use due to high strength-to-weight ratios

• More accurate load distribution to supporting walls and foundations

Even with trusses, foundation and wall design must satisfy OBC load combinations to ensure safe load transfer.

Traditional Roofs: Flexibility vs. Efficiency

© by SchwammKL

Traditional roofs use rafters, ridge boards, and collar ties built on-site. From an engineering standpoint, they offer design flexibility but introduce higher dependence on workmanship.

Limitations include:

• Greater layout complexity and potential alignment errors

• Lower efficiency for long spans compared to trusses

• Increased labour time and variability in performance

When comparing roof rafters vs trusses, rafters excel in custom or heritage projects, while trusses provide superior consistency and efficiency in most modern builds.

Common Types of Roof Trusses

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Several roof truss types are used depending on span, loading, and architectural needs:

• King Post Truss – Effective for short spans

• Queen Post Truss – Suitable for moderate spans

• Fink Truss – The most common residential option

• Howe Truss – Designed for larger spans and higher loads

These types of roof trusses can be adapted for slope, materials, and detailing based on structural requirements.

Code Compliance and Engineering Requirements

All roof truss design in Ontario must comply with:

• OBC requirements for ULS and SLS

• Fire-resistance specifications for applicable building types

• CSA O86: Engineering Design in Wood

Prefabricated trusses must be manufactured in certified facilities and delivered with engineer-sealed truss layout drawings and design sheets, ensuring full structural engineering compliance.

Conclusion

Both roof trusses and traditional rafter systems can achieve strong, code-compliant performance when designed correctly. Roof trusses offer predictable load paths, material efficiency, and excellent dimensional control, while rafter framing remains a flexible option for custom rooflines and restoration projects.

At Parsways, we provide OBC-compliant structural design, roof framing reviews, and engineered solutions for both truss systems and traditional rafter assemblies across Ontario.

Co-authored by Khashayar Lotfalian and Negin Amani.

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FAQs

1. Why are roof trusses preferred in structural engineering?

They offer predictable load paths, higher stiffness, and consistent factory-controlled quality.

2. Can roof trusses eliminate interior bearing walls?

Often yes. Their geometry allows wider open-concept layouts without extra supports.

3. Are steel roof trusses better for long spans?

Steel provides higher strength and reduced deflection, making it beneficial for larger or heavier roof systems.