TL;DR
Metal trusses offer superior strength-to-weight ratio and longer spans, while wood trusses are cost-effective and environmentally friendly. Choice depends on building requirements, budget, and local conditions.
Commercial building design demands careful consideration of roofing systems, with trusses being a crucial structural component. The choice between metal and wood trusses can significantly impact a project’s success, cost, and longevity.
Structural Performance
Metal trusses, particularly steel, excel in strength-to-weight ratio. They can span distances up to 400 feet without intermediate support, making them ideal for warehouses and industrial facilities. Their uniform manufacturing process ensures consistent performance and minimal deflection under load.Wood trusses, while limited to spans typically under 80 feet, offer excellent compression strength relative to their weight. Engineered wood products like glulam can increase this span capability while maintaining wood’s natural advantages.
Cost Considerations
Initial costs favor wood trusses, often running 20-30% cheaper than metal alternatives. However, the total cost equation isn’t straightforward:
Metal trusses:
- Higher material costs
- Lower installation labor costs
- Minimal maintenance requirements
- Longer lifespan (50+ years)
Wood trusses:
- Lower material costs
- Higher installation labor costs
- Regular maintenance needed
- 30-40 year typical lifespan
Design Flexibility
Metal trusses offer superior design flexibility with:
- Longer clear spans
- Ability to handle complex geometries
- Better integration with mechanical systems
- Easier modification for future renovations
Wood trusses excel in:
- Simpler designs
- Traditional architectural aesthetics
- Easier on-site modifications
- Better thermal performance
Environmental Impact
Wood trusses have clear environmental advantages:
- Renewable resource
- Lower embodied energy
- Carbon sequestration
- Biodegradable at end-of-life
Metal trusses counter with:
- High recycling potential
- Longer service life
- Reduced material usage due to strength
- Lower transportation emissions due to weight
Fire Performance
Contrary to common perception, both materials have distinct fire-resistance characteristics. Heavy timber trusses char on the outside while maintaining structural integrity. Steel trusses maintain strength until reaching critical temperatures (around 1000°F), then fail rapidly without warning. Both typically require additional fire protection in commercial applications.
Regional Considerations
Climate and location significantly influence truss selection:
- High humidity regions: Metal trusses resist moisture-related issues
- Seismic zones: Both perform well with proper design
- Coastal areas: Metal requires special corrosion protection
- Cold climates: Wood offers better thermal performance
Installation and Construction
Metal trusses typically require:
- Crane installation
- Skilled welders
- Precise manufacturing tolerances
- Factory fabrication
Wood trusses offer:
- On-site modification capability
- Standard carpentry skills
- More forgiving tolerances
- Local fabrication options
Maintenance Requirements
Metal trusses need:
- Periodic inspection for corrosion
- Joint and connection checks
- Paint or coating maintenance
Wood trusses require:
- Regular moisture content monitoring
- Termite and pest inspection
- Crack and split checking
- Connection tightness verification
FAQ
Q: Which type of truss is better for green building certification?
A: Wood trusses typically earn more points in green building systems due to renewability and lower embodied energy.
Q: Can metal and wood trusses be used together?
A: Yes, hybrid systems are possible and can optimize the advantages of both materials.
Q: What’s the typical cost difference per square foot?
A: Wood trusses average $7-15/sq ft, while metal trusses range from $12-25/sq ft, depending on design complexity and location.
Q: How do insurance rates compare?
A: Insurance rates vary by jurisdiction but often favor metal trusses due to fire resistance and durability.
Q: Which requires more frequent replacement?
A: Wood trusses typically need replacement after 30-40 years, while metal trusses can last 50+ years with proper maintenance.
The choice between metal and wood trusses ultimately depends on specific project requirements, budget constraints, and local conditions. Both systems have proven track records in commercial construction, and either can be the optimal choice when properly specified and installed.