Mass timber is made by fastening together layers of solid-sawn lumber, veneer, or other wood elements with adhesives, nails, or screws to create large structural components. These components are then used for walls, floors, and roofs in various building types.
Here's a more detailed breakdown:
1. Material Selection and Preparation:
- The process starts with selecting suitable wood species. Softwoods like spruce, pine, and fir are commonly used due to their strength-to-weight ratio and availability.
- The wood is then dried to a specific moisture content to ensure stability and prevent warping or cracking.
2. Layup and Lamination/Fastening:
- For Cross-Laminated Timber (CLT): Layers of lumber are stacked in alternating directions (typically 90 degrees) to improve dimensional stability and strength in both directions. Adhesive is applied between the layers, and the entire panel is pressed together under high pressure to bond the layers. Screws or nails can also be used in conjunction with adhesives.
- For Nail-Laminated Timber (NLT): Dimension lumber is placed on edge and fastened together with nails. This is one of the oldest forms of mass timber.
- For Glue-Laminated Timber (Glulam): Individual wood laminations are glued together with high-strength adhesives, with the wood grain running parallel to the length of the beam or column. This allows for long spans and complex shapes.
- For Dowel-Laminated Timber (DLT): Similar to NLT, but uses wooden dowels instead of nails or screws for connecting the lumber pieces. The dowels are often made of hardwood to increase strength.
3. Pressing and Curing:
- After the layers are assembled, the mass timber element is pressed to ensure proper bonding and consolidation.
- The adhesive is then allowed to cure for a specific amount of time, depending on the type of adhesive used.
4. Finishing and Fabrication:
- Once the adhesive has cured, the mass timber panel or beam is finished to the desired dimensions and surface quality. This may involve sanding, planing, and applying a protective coating.
- The panels can be fabricated with precise cutouts and openings for windows, doors, and mechanical systems using CNC (Computer Numerical Control) machines.
5. Quality Control:
- Throughout the manufacturing process, rigorous quality control measures are implemented to ensure that the mass timber elements meet the required standards for strength, durability, and dimensional accuracy.
Different Mass Timber Products and Their Manufacturing Methods:
| Mass Timber Type | Manufacturing Method | Key Characteristics |
|---|---|---|
| Cross-Laminated Timber (CLT) | Layers of lumber glued and pressed together with alternating grain directions. | High dimensional stability, strength in multiple directions, suitable for walls, floors, and roofs. |
| Nail-Laminated Timber (NLT) | Dimension lumber placed on edge and fastened together with nails. | Simple manufacturing, cost-effective, suitable for floors and roofs. |
| Glue-Laminated Timber (Glulam) | Individual wood laminations glued together with parallel grain direction. | High strength-to-weight ratio, long spans, complex shapes possible, suitable for beams, columns, and arches. |
| Dowel-Laminated Timber (DLT) | Dimension lumber connected with hardwood dowels. | Adhesive-free option, good acoustic performance, suitable for floors, walls, and roofs. |
| Laminated Veneer Lumber (LVL) | Layers of wood veneer glued together with parallel grain direction. | High strength and stiffness, consistent material properties, suitable for beams, headers, and rim boards. |
In summary, mass timber is a versatile building material created by bonding together layers of wood in various configurations, offering sustainable and structurally sound alternatives to concrete and steel in construction.
