Dowel-laminated timber (DLT)

What is DLT?

DLT is a mass timber panel product created by stacking dimension lumber together on its edge (left) or cross laminating them (right), fit together with hardwood dowels.

How is DLT made?

DLT is made using graded lumber which is structurally finger jointed, run through a moulder—a machine to cut and shape the wood—and laminated into large panels of DLT. The product is prefabricated into panels using high powered hydraulic press, the hardwood dowels pressed into tight-fit holes of the lamellas—layered panels pressed together—all within a factory-setting.

The product uses the differing moisture content of the softwood and hardwood components to friction-fit the product together. This means differences in moisture of the planks, which shrink, and the dowels, which swell, help lock the panels together.

Typically, sheathing is pre-installed, and exposed faces are finished, then ready for delivery to site. DLT is the only all-wood mass timber product with no metal fasteners, nails or adhesives.

What is DLT used for?

DLT, similar to other mass timber products, is being used for a wide range of building types from offices and schools to commercial and public buildings. It can be used as walls, floor and roof construction. Similar to nail-laminated timber (NLT), DLT panels can be used as stairs and elevator shafts as well as bent and assembled to create curved roof structures.

Similar to other mass timber products, DLT panels can be topped with concrete to form timber concrete composite (TCC), a hybrid system used to reduce cross sections, increase spans and lessen noise transfer and vibrations.

DLT can be run through a molder to produce different aesthetic and acoustic profiles—such as a kerf, chamfer, ease or square edge. Alternating patterns of lumber are used to create various aesthetic appearances. DLT panels can also accommodate mechanical services and sound absorbing insulation, neatly tucked away as part of its cut and design.

Quality control is provided by the ICC certification for the proprietary DLT in North America. The ICC report demonstrates compliance of the DLT product with the requirements of the International Building Code. The report provides structural capacities for DLT panels and shows how to calculate fire resistance ratings.

Performance of DLT

DLT is permitted and is safe to be exposed when in accordance with building codes, as their large mass provides inherent resistance to fire. DLT, like other mass timber products, naturally resists fire because it chars. In the event of a fire, this char on the outside forms a protective layer while retaining strength. This slows combustion significantly, allowing time to evacuate the building safely. Tests show DLT delivers two hours of fire resistance.

Mass timber’s fire safety is backed up by rigorous fire testing in Canada and around the world (external link).

Similar to other wood products, DLT will not rot or acquire mould when designed and installed correctly. Weather protection during transport is important and exposure to water should be avoided. To ensure long-term durability, steps should be taken to keep DLT dry during construction and installation. Once installed, an air and water vapour barrier is used to protect the wood.

Radium Hot Springs Community Hall and Librar y | Photo credit: Dave Best

DLT can be a substitute for conventional concrete and steel construction, replacing these carbon intensive materials with a renewable, low carbon alternative. Compared to concrete, DLT structures can be installed in a shorter time period, in any season all year round. DLT can be used in place of concrete slabs and steel decking in commercial, institutional and residential buildings.

DLT’s all timber-design, with no metal connectors, means it can be easily processed and cut using computerized numerical control (CNC) machinery or modified on site. Adhesives and glue are not generally used in the fabrication of DLT, unlike other products.