Trusses vs. Rafters: Six Key Differences in Roof Framing

1. Structural Function

• Trusses: Engineered rigid frameworks (triangulated) transferring roof loads to walls. Span long distances without interior support.
• Rafters: Individual sloping beams from ridge to eaves. Support roofing materials directly.

2. Design and Fabrication

• Trusses: Pre-engineered, factory-built, delivered complete. Faster installation.
• Rafters: Cut and assembled on-site. Require skilled carpentry, precise layout.

3. Complexity

• Trusses: Complex internal geometry (webs, chords, connections). Calculated for specific loads.
• Rafters: Simpler beams. Birdsmouth cuts, ridge board, collar ties.

4. Spacing

• Trusses: Typically 600-1200mm (24-48") on center
• Rafters: Typically 400-600mm (16-24") on center

5. Load Capacity and Span

• Trusses: Superior for long spans (12m+), heavy loads (snow, tile, solar)
• Rafters: Limited spans without purlins/beams. Better for simple, smaller roofs.

6. Cost Considerations

• Trusses: Higher material cost, lower labor. Economical for large/complex roofs.
• Rafters: Lower material, higher labor. Economical for small/simple roofs or custom shapes.

Modern Practice

Trusses dominate production housing (>80% US). Rafters persist in custom homes, renovations, exposed-beam aesthetics, and complex roof geometries where truss fabrication is impractical.