Mass timber construction utilizes various types of engineered wood products, rather than a single species of wood.
Understanding Mass Timber Wood Types
Mass timber refers to a category of engineered wood building products known for their strength, stability, and sustainability. It isn't defined by a specific species of wood (like pine or spruce, although these are often used), but rather by the way wood elements are manufactured into larger structural components. These components are typically prefabricated and used for walls, floors, and roofs in mid-rise and tall buildings.
The mass timber family encompasses several distinct product types, each with unique characteristics and applications in construction.
| Mass Timber Product Type | Abbreviation(s) | Description Overview |
|---|---|---|
| Cross-Laminated Timber | CLT | Layers of lumber glued with alternating grain direction. |
| Nail-Laminated Timber | NLT | Lumber boards fastened together with nails. |
| Dowel-Laminated Timber | DLT | Lumber boards joined with hardwood dowels. |
| Glue-Laminated Timber | Glulam, GLT | Layers of dimensional lumber bonded with adhesive. |
| Structural Composite Lumber | SCL | Engineered wood made from veneer or strands. |
These engineered products transform smaller lumber pieces into large-scale structural elements capable of bearing significant loads over long spans, making them viable alternatives to steel and concrete in many applications.
Key Engineered Wood Products in Mass Timber
The following types of engineered wood products are commonly used in mass timber construction:
- Cross-Laminated Timber (CLT): Made by layering lumber boards in alternating directions (typically 90 degrees to each other) and bonding them together with structural adhesives. This alternating grain pattern provides exceptional dimensional stability and strength in both directions, making CLT excellent for panels used in walls, floors, and roofs.
- Nail-Laminated Timber (NLT): Constructed by stacking dimension lumber boards on edge and fastening them together with nails. NLT is one of the older forms of mass timber and is often used for floor and roof structures. It does not use adhesives, relying solely on mechanical fastening.
- Dowel-Laminated Timber (DLT): Similar to NLT, DLT is created by stacking dimension lumber boards on edge, but instead of nails, it uses hardwood dowels friction-fit into place to hold the boards together. Like NLT, it is an adhesive-free option, primarily used for floor and roof panels.
- Glue-Laminated Timber (Glulam or GLT): Produced by bonding together individual laminations of dimension lumber with durable, moisture-resistant structural adhesives. Glulam is typically used for beams and columns due to its high strength-to-weight ratio and ability to be manufactured in long lengths and custom shapes.
- Some types of Structural Composite Lumber (SCL): This category includes products like Laminated Veneer Lumber (LVL), Parallel Strand Lumber (PSL), and Laminated Strand Lumber (LSL). SCL products are made by bonding together wood veneers, strands, or flakes with adhesives under heat and pressure. While often used for beams, headers, and columns in light-frame construction, certain high-strength varieties and applications fall under the mass timber umbrella for their structural capacity.
These engineered wood products form the backbone of modern mass timber buildings, allowing for rapid assembly, reduced carbon footprint compared to traditional materials, and aesthetically pleasing exposed wood structures. The specific species of wood used to make these products can vary depending on regional availability and structural requirements, but common choices include spruce, pine, fir, and other softwoods.
