Cross-Laminated Timber (CLT)
Cross-Laminated Timber (CLT) is an engineered wood panel product made from layers of lumber boards stacked crosswise and bonded together, creating a strong, stable, and versatile building material that's revolutionizing sustainable construction.
Composition
Multiple layers (typically 3, 5, 7, or 9) of kiln-dried lumber boards stacked at right angles to one another and bonded with structural adhesives under pressure. Each layer's grain direction runs perpendicular to adjacent layers, creating a panel with exceptional strength and stability.
Properties
Density
28-35 lbs/ft³
Varies based on wood species used, typically about one-fifth the weight of concrete.
Bending Strength
2,400-3,000 psi
High strength-to-weight ratio, with performance comparable to concrete in many applications.
Dimensional Stability
Excellent
Cross-laminated construction minimizes expansion, contraction, and warping due to moisture or temperature changes.
Fire Resistance
1-2 hour rating
Forms a protective char layer when exposed to fire, with predictable char rates of approximately 1.5 inches per hour.
Thermal Resistance
R-1.25 per inch
Provides moderate thermal insulation, often supplemented with additional insulation materials.
Sound Transmission Class (STC)
32-34 (bare panels)
Basic sound insulation properties that can be enhanced with additional acoustic treatments.
Applications
Structural Walls
Used as load-bearing and shear walls in residential and commercial buildings, providing both structural support and finished surfaces.
Floor and Roof Systems
Serves as structural floor and roof panels, offering high load-bearing capacity and spanning capabilities.
Multi-Story Buildings
Increasingly used for mid-rise and high-rise construction (up to 18+ stories) as a sustainable alternative to concrete and steel.
Hybrid Construction
Combined with concrete, steel, or other materials in hybrid structural systems to optimize performance and cost.
Prefabricated Modular Construction
Manufactured off-site as complete wall, floor, or roof assemblies with pre-cut openings for doors, windows, and utilities.
Exposed Architectural Elements
Often left exposed as interior finish surfaces, providing natural aesthetic appeal in residential and commercial spaces.
Advantages
- Exceptional strength-to-weight ratio compared to concrete and steel
- Rapid construction time due to prefabrication and lighter weight
- Carbon sequestration - stores carbon captured during tree growth
- Renewable resource when sourced from sustainably managed forests
- Excellent dimensional stability and predictable structural performance
- Natural fire resistance through charring behavior
- Attractive natural appearance when used as exposed finish
- Precision manufacturing with CNC technology for tight tolerances
- Reduced construction waste compared to traditional methods
Limitations
- Higher initial cost compared to traditional light-frame wood construction
- Limited domestic manufacturing capacity in some regions
- Requires protection from prolonged moisture exposure
- Specialized design knowledge and connection details required
- May require additional treatments for acoustic performance
- Building code adoption and approval processes still evolving in some jurisdictions
- Transportation limitations for very large panels
- Some products use formaldehyde-based adhesives (though many now use formaldehyde-free options)
Sustainability Profile
High sustainability profile. CLT is made from renewable wood resources, often including smaller-dimension lumber that might not be suitable for traditional applications. When sourced from sustainably managed forests (FSC or PEFC certified), it represents a truly renewable building material. CLT buildings sequester carbon for their lifetime, and the manufacturing process produces fewer greenhouse gas emissions compared to concrete or steel production. The prefabricated nature reduces construction waste, and the material's durability contributes to long building lifespans. End-of-life considerations include potential for reuse, though adhesives may complicate full recycling.