Truss vs. Rafter Framing: A Structural Review for Ontario
- Parsways
- Feb 27, 2023
- 3 min read
Updated: Oct 16
When constructing a wood frame structure, the roof system plays a fundamental role in the building’s overall stability and load management. Beyond aesthetics, roof design directly affects the distribution of dead and live loads, long-term deflection, and overall service life.
Two major approaches are commonly used: truss roofs and traditional framed roofs.
This guide compares both in terms of cost, structural performance, and design efficiency, offering a technically grounded overview for builders and homeowners alike.
What Are Truss Roofs?
A truss roof consists of a prefabricated network of top chords, bottom chords, and web members designed to transfer loads efficiently through triangular geometry.
Each truss is manufactured off-site based on engineered calculations to ensure consistency and code compliance. This approach minimizes on-site labor, speeds up installation, and reduces the potential for framing inaccuracies.
Because of their predictable load paths, roof trusses are ideal for long-span structures or complex roof profiles where dimensional precision and material efficiency are critical.
They can be produced in wood for traditional framing systems or steel for higher strength and reduced long-term deflection.
Structural Principles of Prefabricated Truss Systems
The key advantage of truss systems lies in how they handle gravity and lateral loads. Their triangulated form provides exceptional rigidity, distributing weight uniformly and reducing stress concentrations that often occur in conventional framing.
This reduces the need for interior load-bearing walls, allowing greater design freedom in open-plan layouts.
Truss roofs are less prone to sagging, creep, or settlement, maintaining structural alignment even under snow load and thermal cycles.
When combined with high-quality insulation, roof sheathing, and asphalt shingles, the system delivers excellent long-term performance and energy efficiency.
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Material Efficiency and Project Cost Implications
Prefabricated trusses lower overall project costs by reducing site labor and installation time.
The higher strength-to-weight ratio of trusses can lead to more efficient load distribution, potentially reducing the dead load on supporting walls and foundations.
However, foundation design must still account for controlling load combinations as specified by the building code. From a project coordination standpoint, this system provides predictable performance; similar to using engineered wood members elsewhere in the structure.
Traditional Roofs: Flexibility vs Efficiency
Traditional roofs, framed on-site using rafters, ridge boards, and collar ties, offer greater architectural flexibility, especially in custom designs.
However, this method often requires more manual layout and alignment, increasing the potential for human error and higher labor costs.
While it remains a preferred option for restoration or unique aesthetic projects, traditional framing typically offers lower structural efficiency compared to engineered truss systems.
Common Types of Roof Trusses
Selecting the correct truss configuration ensures the roof performs as intended under various span and load conditions. Common types include:
King Post Truss – Suitable for short spans and simple rooflines.
Queen Post Truss – Provides added stability for moderate spans.
Fink Truss – Common in residential framing for efficient material use.
Howe Truss – Optimized for large spans and higher load demands.
Each type is analyzed and detailed to maintain proper load transfer and structural stability, ensuring compliance with modern building standards.
Styles of roof trusses can be customized for slope, materials, and load requirements—just like the structural choices discussed in Types of Building Foundations in Ontario.
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Code Compliance and Engineering Requirements (OBC 2024 & CSA O86)
Prefabricated trusses are engineered to meet the stringent criteria of the Ontario Building Code, including factored load combinations (ULS) and serviceability limits (SLS) for deflection, as well as prescribed fire-resistance ratings for specific building types.
Prefabricated trusses are designed and reviewed in accordance with engineering specifications to meet these standards before being delivered on-site. This not only reduces construction errors but also ensures consistent quality across multiple projects.
All prefabricated wood trusses used in Ontario must be designed in accordance with CSA O86, 'Engineering Design in Wood', and manufactured by a certified facility.
Each delivery must be accompanied by engineer-sealed truss layout drawings and individual truss design sheets specifying loads, reactions, and handling requirements as mandated by OBC 9.23.13.11.
Conclusion
For most wood-frame buildings, truss roofs provide a refined balance of strength, cost efficiency, and design precision.
While traditional roofs maintain their place in certain architectural applications, the engineered truss system remains the superior choice for modern construction where performance, reliability, and efficiency are essential.
Co-authored by Parsways and Negin Amani.
