A builder is constructing a large commercial warehouse with a clear span of 60 feet. The design calls for a heavy timber roof system. Considering the span and common heavy timber elements, which of the following would be the most appropriate and structurally efficient choice for the main roof framing members?
- AWood I-joists with steel flitch plates.
- BGlued Laminated Timber (Glulam) beams.
- CLight-gauge steel trusses.
- DSolid sawn timbers, 12x24 nominal on 8-foot centers.
Show answer & explanationAnswer & explanation
Correct answer: B. Glued Laminated Timber (Glulam) beams.
For a 60-foot clear span in heavy timber roof construction, Glued Laminated Timber (Glulam) beams are the most appropriate and structurally efficient choice. Glulam beams can be manufactured in very long lengths and large cross-sections, providing superior strength and stiffness for long spans while maintaining the aesthetic and fire-resistant properties of heavy timber. Solid sawn timbers of that size are extremely rare and costly, and I-joists or steel trusses fall outside the 'heavy timber' classification.
Why the other options are wrong
- A. Wood I-joists are light-frame elements, not considered heavy timber, and typically not suitable for a 60-foot clear span without significant reinforcement.
- C. Light-gauge steel trusses are not a heavy timber element and would fall under steel construction, not wood.
- D. Solid sawn timbers of sufficient size for a 60-foot span are extremely difficult to source, very expensive, and often less efficient than Glulam.
Heavy Timber Long Spans
Structural elements capable of spanning significant distances (e.g., 40+ feet) while maintaining the aesthetic and fire-resistive properties of heavy timber construction.
- Glulam is ideal for long spans in heavy timber.
- Solid sawn timbers become impractical at very long spans.
- Requires engineered solutions for structural efficiency.
Memory trick: Long spans need engineered wood's grace, not just a big, old timber's face.