Advancements in wood product technology and systems are driving the momentum for innovative buildings in Canada. Products such as cross-laminated timber (CLT), nailed-laminated timber (NLT), glued-laminated timber (GLT), laminated strand lumber (LSL), laminated veneer lumber (LVL) and other large-dimensioned structural composite lumber (SCL) products are part of a bigger classification known as ‘mass timber’.

Although mass timber is an emerging term, traditional post-and-beam (timber frame) construction has been around for centuries. Today, mass timber products can be formed by mechanically fastening and/or bonding with adhesive smaller wood components such as dimension lumber or wood veneers, strands or fibres to form large pre-fabricated wood elements used as beams, columns, arches, walls, floors and roofs. Mass timber products have sufficient volume and cross-sectional dimensions to offer significant benefits in terms of fire, acoustics and structural performance, in addition to providing construction efficiency.

A truss is a structural frame relying on a triangular arrangement of webs and chords to transfer loads to reaction points. This geometric arrangement of the members gives trusses high strength-to-weight ratios, which permit longer spans than conventional framing. Light-frame truss can commonly span up to 20 m (60 ft), although longer spans are also feasible.

The first light-frame trusses were built on-site using nailed plywood gusset plates. These trusses offered acceptable spans but demanded considerable time to build. Originally developed in the United States in the 1950s, the metal connector plate transformed the truss industry by allowing efficient prefabrication of short and long span trusses. The light-gauge metal connector plates allow for the transfer of load between adjoining members through punched steel teeth that are embedded into the wood members. Today, light-frame wood trusses are widely used in single- and multi-family residential, institutional, agricultural, commercial and industrial construction.

The shape and size of light-frame trusses is restricted only by manufacturing capabilities, shipping limitations and handling considerations. Trusses can be designed as simple or multi-span and with or without cantilevers. Economy, ease of fabrication, fast delivery and simplified erection procedures make light-frame wood trusses competitive in many roof and floor applications. Their long span capability often eliminates the need for interior load bearing walls, offering the designer flexibility in floor layouts. Roof trusses offer pitched, sloped or flat roof configurations, while also providing clearance for insulation, ventilation, electrical, plumbing, heating and air conditioning services between the chords.

Light-frame wood trusses are prefabricated by pressing the protruding teeth of the steel truss plate into 38 mm (2 in) wood members, which are pre-cut and assembled in a jig. Most trusses are fabricated using 38 x 64 mm (2 x 3 in) to 38 x 184 mm (2 x 8 in) visually graded and machine stress-rated (MSR) lumber. To provide different grip values, the truss connector plates are stamped from galvanized light-gauge sheet steel of different grades and gauge thicknesses. Many sizes of truss plates are manufactured to suit any shape or size of truss or load to be carried.

Light frame trusses are manufactured according to standards established by the Truss Plate Institute of Canada. The capacities for the plates vary by manufacturer and are established through testing. Truss plates must conform to the requirements of CSA O86 and must be approved by the Canadian Construction Materials Centre (CCMC). To obtain approval, the truss plates are tested in accordance with CSA S347. During design, light-frame trusses are generally engineered by the truss plate manufacturer on behalf of the truss fabricator.

When light-frame trusses arrive at the job site they should be checked for any permanent damage such as cross breaks in the lumber, missing or damaged metal connector plates, excessive splits in the lumber, or any damage that could impair the structural integrity of the truss. Whenever possible, trusses should be unloaded in bundles on dry, relatively smooth ground. They should not be unloaded on rough terrain or uneven spaces that could result in undue lateral strain that could possibly distort the metal connector plates or damage parts of the trusses.

Light-frame trusses can be stored horizontally or vertically. If stored in the horizontal position, trusses should be supported on blocking spaced at 2.4 to 3 m (8 to 10 ft) centres to prevent lateral bending and reduce moisture gain from the ground. When stored in the vertical position, trusses should be placed on a stable horizontal surfaced and braced to prevent toppling or tipping. If trusses need to be stored for an extended period of time measures must be taken to protect them from the elements, keeping the trusses dry and well ventilated.

Light-frame trusses require temporary bracing during erection, prior to the installation of permanent bracing. Truss plates should not be used with incised lumber. Contact the truss manufacturer for further guidance on the use of light-frame trusses in corrosive environments, wet service conditions, or when treated with a fire retardant.

For further information, refer to the following resources:

• Canadian Wood Truss Association
• Truss Plate Institute of Canada
• CSA O86 Engineering design in wood
• CSA S347 Method of test for evaluation of truss plates used in lumber joints
• Canadian Construction Materials Centre

Dimension lumber is solid sawn wood that is less than 89 mm (3.5 in) in thickness. Lumber can be referred to by its nominal size in inches, which means the actual size rounded up to the nearest inch or by its actual size in millimeters. For instance, 38 × 89 mm (1-1/2 × 3-1/2 in) material is referred to nominally as 2 × 4 lumber. Air-dried or kiln dried lumber (S-Dry), having a moisture content of 19 percent or less, is readily available in the 38 mm (1.5 in) thickness. Dimension lumber thicknesses of 64 and 89 mm (2-1/2 and 3-1/2 in) are generally available as surfaced green (S-Grn) only, i.e., moisture content is greater than 19 percent.

The maximum length of dimension lumber that can be obtained is about 7 m (23 ft), but varies throughout Canada.

The predominant use of dimension lumber in building construction is in framing of roofs, floors, shearwalls, diaphragms, and load bearing walls. Lumber can be used directly as framing materials or may be used to manufacture engineered structural products, such as light frame trusses or prefabricated wood I-joists. Special grade dimension lumber called lamstock (laminating stock) is manufactured exclusively for glulam.

Quality assurance of Canadian lumber is achieved via a complex system of product standards, engineering design standards and building codes, involving grading oversight, technical support and a regulatory framework.

Checking and splitting
Fingerjoined Lumber
Lumber Sizes
Moisture content
Surface Smoothness

Prefabricated wood I-joists are proprietary structural wood members that consist of fingerjoined solid sawn lumber or laminated veneer lumber (LVL) flanges attached to a plywood or oriented strand board (OSB) web using adhesive. Web panel joints are glued and mated by several methods such as butting of square panel ends, scarfing of the panel ends, or shaping of either a toothed or tongue and groove type joint. Exterior rated, waterproof adhesives such as phenol-formaldehyde and phenol-resorcinol are the principally used for the web to web and web to flange joints. Different combinations of flange and web materials using alternative connections between the web and the flanges are available from several manufacturers (refer to Figure 3.20, below). Wood I-joists are available in a variety of standard depths and in lengths of up to 20 m (66 ft).

Each manufacturer produces I-joists with unique strength and stiffness characteristics. To ensure that proprietary products have been manufactured under a quality assurance program supervised by an independent third-party certification organization, manufacturers typically have their products evaluated and registered under the requirements and guidelines of the Canadian Construction Material Centre (CCMC).

The cross-sectional “I” shape of these structural wood products provides a higher strength to weight ratio than traditional solid sawn lumber. The uniform stiffness, strength, and light weight of these prefabricated elements allow for use in longer span joist and rafter applications for both residential and commercial construction. Wood I-joists are usually manufactured using untreated flange and web material and therefore, are typically not used for exterior applications. Wood I-joist are also dimensionally stable as they are manufactured with a moisture content between 6 and 12 %.

For the installation of mechanical and electrical services, many manufacturers provide requirements and guidance for the shape, size and location of openings, notches, holes and cuts. Most wood I-joist suppliers also stock standard joist hangers and other prefabricated connection hardware specially designed for use with wood I-joists.

For further information on wood I-joists, refer to the following resources:

APA – The Engineered Wood Association

Canadian Construction Material Centre (CCMC), Institute for Research in Construction (NRC)

Wood I-Joist Manufacturers Association (WIJMA)

CSA O86 Engineering design in wood

ASTM D5055 Standard Specification for Establishing and Monitoring Structural Capacities of Prefabricated Wood I-Joists

By using roundwood that is often not be suitable for lumber production, wood-based panels make efficient use of the forest resource by providing engineered wood products with defined strength and stiffness properties.

Wood-based structural panels such as plywood and oriented strand board (OSB) are widely used in residential and commercial construction. Wood-based panels are often overlaid on joists or light frame trusses and used as structural sheathing for floor, roofs and wall assemblies. These products provide rigidity to the supporting main structural members in addition to their function as a component of the building envelope. In addition, they are often an integral component of the lateral force resisting system of a wood building.

In order to qualify for a particular end use, such as structural sheathing, flooring or exterior siding, wood-based panels must meet performance criteria related to three aspects: structural performance, physical properties and bond performance. For more information on performance rating and potential end uses of wood-based panel products, refer to APA – The Engineered Wood Association.

Laminated Veneer Lumber (LVL)

First used during World War II to make airplane propellers, laminated veneer lumber (LVL) has been available as a construction product since the mid-1970s. LVL is the most widely used structural composite lumber (SCL) product and provides attributes such as high strength, high stiffness and dimensional stability. The manufacturing process of LVL enables large members to be made from relatively small trees, providing efficient utilization of forest resources. LVL is commonly fabricated using wood species such as Douglas fir, Larch, Southern yellow pine and Poplar.

LVL is used primarily as structural framing for residential and commercial construction. Common applications of LVL in construction include headers and beams, hip and valley rafters, scaffold planking, and the flange material for prefabricated wood I-joists. LVL can also been used in roadway sign posts and as truck bed decking.

LVL is made of dried and graded wood veneer which is coated with a waterproof phenol-formaldehyde resin adhesive, assembled in an arranged pattern, and formed into billets by curing in a heated press. The LVL billet is then sawn to desired dimensions depending on the end use application.

The grain of each layer of veneer runs in the same (long) direction with the result that LVL is able to be loaded on its short edge (strong axis) as a beam or on its wide face (weak axis) as a plank. This type of lamination is called parallel-lamination and produces a material with greater uniformity and predictability than engineered wood products fabricated using cross-lamination, such as plywood.

LVL is a solid, highly predictable, uniform lumber product due to the fact that natural defects such as knots, slope of grain and splits have been dispersed throughout the material or have been removed altogether during the manufacturing process.

The most common thickness of LVL is 45 mm (1-3/4 in), from which wider beams can be easily constructed by fastening multiple LVL plies together on site. LVL can also be manufactured in thicknesses from 19 mm (3/4 in) to 178 mm (7 in). Commonly used LVL beam depths are 241 mm (9-1/2 in), 302 mm (11-7/8 in), 356 mm (14 in), 406 mm (16 in), 476 mm (18-3/4 in) and 606 mm (23-7/8 in). Other widths and depths might also be available from specific manufacturers. LVL is available in lengths up to 24.4 m (80 ft), while more common lengths are 14.6 m (48 ft), 17 m (56 ft), 18.3 m (60 ft) and 20.1 m (66 ft). LVL can easily be cut to length at the jobsite.

All special cutting, notching or drilling should be done in accordance with manufacturer’s recommendations. LVL is a wood-based product with similar fire performance to a comparably sized solid sawn lumber or glued-laminated beam. Manufacturer’s catalogues and evaluation reports are the primary sources of information for design, typical installation details and performance characteristics.

LVL is mainly used as a structural element, most often in concealed spaces where appearance is not important. Finished or architectural grade appearance is available from some manufacturers, usually at an additional cost. However, when it is desired to use LVL in applications where appearance is important, common wood finishing techniques can be used to accent grain and to protect the wood surface. In finished appearance, LVL resembles plywood or lumber on the wide face.

As with any other wood product, LVL should be protected from the weather during jobsite storage and after installation. Wrapping of the product for shipment to the job site is important in providing moisture protection. End and edge sealing of the product will enhance its resistance to moisture penetration.

LVL is a proprietary product and therefore, the specific engineering properties and sizes are unique to each manufacturer. Thus, LVL does not have a common standard of production and common design values. Design values are derived from test results analysed in accordance with CSA O86 and ASTM D5456 and the design values are reviewed and approved by the Canadian Construction Materials Centre (CCMC). Products meeting the CCMC guidelines receive an Evaluation Number and Evaluation Report that includes the specified design strengths, which are subsequently listed in CCMC’s Registry of Product Evaluations. The manufacturer’s name or product identification and the stress grade is marked on the material at various intervals, but due to end cutting it may not be present on every piece.

For further information, refer to the following resources:

APA – The Engineered Wood Association

Canadian Construction Materials Centre (CCMC), Institute for Research in Construction

CSA O86 Engineering design in wood

ASTM D5456 Standard Specification for Evaluation of Structural Composite Lumber Products

Laminated Strand Lumber (LSL)

Laminated Strand Lumber (LSL) is one of the more recent structural composite lumber (SCL) products to come into widespread use. LSL provides attributes such as high strength, high stiffness and dimensional stability. The manufacturing process of LSL enables large members to be made from relatively small trees, providing efficient utilization of forest resources. LSL is commonly fabricated using fast growing wood species such as Aspen and Poplar.

LSL is used primarily as structural framing for residential, commercial and industrial construction. Common applications of LSL in construction include headers and beams, tall wall studs, rim board, sill plates, millwork and window framing. LSL also offers good fastener-holding strength.

Similar to parallel strand lumber (PSL) and oriented strand lumber (OSL), LSL is made from flaked wood strands that have a length-to-thickness ratio of approximately 150. Combined with an adhesive, the strands are oriented and formed into a large mat or billet and pressed. LSL resembles oriented strand board (OSB) in appearance as they are both fabricated from the similar wood species and contain flaked wood strands, however, unlike OSB, the strands in LSL are arranged parallel to the longitudinal axis of the member.

LSL is a solid, highly predictable, uniform engineered wood product due to the fact that natural defects such as knots, slope of grain and splits have been dispersed throughout the material or have been removed altogether during the manufacturing process. Like other SCL products such as LVL and PSL, LSL offers predictable strength and stiffness properties and dimensional stability that minimize twist and shrinkage.

All special cutting, notching or drilling should be done in accordance with manufacturer’s recommendations. Manufacturer’s catalogues and evaluation reports are the primary sources of information for design, typical installation details and performance characteristics.

As with any other wood product, LSL should be protected from the weather during jobsite storage and after installation. Wrapping of the product for shipment to the job site is important in providing moisture protection. End and edge sealing of the product will enhance its resistance to moisture penetration.

LSL is a proprietary product and therefore, the specific engineering properties and sizes are unique to each manufacturer. Thus, LSL does not have a common standard of production and common design values. Design values are derived from test results analysed in accordance with CSA O86 and ASTM D5456 and the design values are reviewed and approved by the Canadian Construction Materials Centre (CCMC). Products meeting the CCMC guidelines receive an Evaluation Number and Evaluation Report that includes the specified design strengths, which are subsequently listed in CCMC’s Registry of Product Evaluations. The manufacturer’s name or product identification and the stress grade is marked on the material at various intervals, but due to end cutting it may not be present on every piece.

For further information, refer to the following resources:

APA – The Engineered Wood Association

Canadian Construction Materials Centre (CCMC), Institute for Research in Construction

CSA O86 Engineering design in wood

ASTM D5456 Standard Specification for Evaluation of Structural Composite Lumber Products

Oriented Strand Lumber (OSL)

Oriented Strand Lumber (OSL) provides attributes such as high strength, high stiffness and dimensional stability. The manufacturing process of OSL enables large members to be made from relatively small trees, providing efficient utilization of forest resources.

OSL is used primarily as structural framing for residential, commercial and industrial construction. Common applications of OSL in construction include headers and beams, tall wall studs, rim board, sill plates, millwork and window framing. OSL also offers good fastener-holding strength.

Similar to laminated strand lumber (LSL), OSL is made from flaked wood strands that have a length-to-thickness ratio of approximately 75. The wood strands used in OSL are shorter than those in LSL. Combined with an adhesive, the strands are oriented and formed into a large mat or billet and pressed. OSL resembles oriented strand board (OSB) in appearance as they are both fabricated from the similar wood species and contain flaked wood strands, however, unlike OSB, the strands in OSL are arranged parallel to the longitudinal axis of the member.

OSL is a solid, highly predictable, uniform engineered wood product due to the fact that natural defects such as knots, slope of grain and splits have been dispersed throughout the material or have been removed altogether during the manufacturing process. Like other SCL products such as LVL and PSL, OSL offers predictable strength and stiffness properties and dimensional stability that minimize twist and shrinkage.

All special cutting, notching or drilling should be done in accordance with manufacturer’s recommendations. Manufacturer’s catalogues and evaluation reports are the primary sources of information for design, typical installation details and performance characteristics.

As with any other wood product, OSL should be protected from the weather during jobsite storage and after installation. Wrapping of the product for shipment to the job site is important in providing moisture protection. End and edge sealing of the product will enhance its resistance to moisture penetration.

OSL is a proprietary product and therefore, the specific engineering properties and sizes are unique to each manufacturer. Thus, OSL does not have a common standard of production and common design values. Design values are derived from test results analysed in accordance with CSA O86 and ASTM D5456 and the design values are reviewed and approved by the Canadian Construction Materials Centre (CCMC). Products meeting the CCMC guidelines receive an Evaluation Number and Evaluation Report that includes the specified design strengths, which are subsequently listed in CCMC’s Registry of Product Evaluations. The manufacturer’s name or product identification and the stress grade is marked on the material at various intervals, but due to end cutting it may not be present on every piece.

For further information, refer to the following resources:

APA – The Engineered Wood Association

Canadian Construction Materials Centre (CCMC), Institute for Research in Construction

CSA O86 Engineering design in wood

ASTM D5456 Standard Specification for Evaluation of Structural Composite Lumber Products

Parallel Strand Lumber (PSL)

Parallel Strand Lumber (PSL) provides attributes such as high strength, high stiffness and dimensional stability. The manufacturing process of OSL enables large members to be made from relatively small trees, providing efficient utilization of forest resources. In Canada, PSL is fabricated using Douglas fir.

PSL is employed primarily as structural framing for residential, commercial and industrial construction. Common applications of PSL in construction include headers, beams and lintels in light-frame construction and beams and columns in post and beam construction. PSL is an attractive structural material which is suited to applications where finished appearance is important.

Similar to laminated strand lumber (LSL) and oriented strand lumber (OSL), PSL is made from flaked wood strands that are arranged parallel to the longitudinal axis of the member and have a length-to-thickness ratio of approximately 300. The wood strands used in PSL are longer than those used to manufacture LSL and OSL. Combined with an exterior waterproof phenol-formaldehyde adhesive, the strands are oriented and formed into a large billet, then pressed together and cured using microwave radiation.

PSL beams are available in thicknesses of 68 mm (2-11/16 in), 89 mm (3-1/2 in), 133 mm (5-1/4 in), and 178 mm (7 in) and a maximum depth of 457 mm (18 in). PSL columns are available in square or rectangular dimensions of 89 mm (3-1/2 in), 133 mm (5-1/4 in), and 178 mm (7 in). The smaller thicknesses can be used individually as single plies or can be combined for multi-ply applications. PSL can be made in long lengths but it is usually limited to 20 m (66 ft) by transportation constraints.

PSL is a solid, highly predictable, uniform engineered wood product due to the fact that natural defects such as knots, slope of grain and splits have been dispersed throughout the material or have been removed altogether during the manufacturing process. Like the other SCL products (LVL, LSL and OSL), PSL offers predictable strength and stiffness properties and dimensional stability. Manufactured at a moisture content of 11 percent, PSL is less prone to shrinking, warping , cupping, bowing and splitting.

All special cutting, notching or drilling should be done in accordance with manufacturer’s recommendations. Manufacturer’s catalogues and evaluation reports are the primary sources of information for design, typical installation details and performance characteristics.

PSL exhibits a rich texture and retains numerous dark glue lines. PSL can be machined, stained, and finished using the techniques applicable to sawn lumber. PSL members readily accept stain to enhance the warmth and texture of the wood. All PSL is sanded at the end of the production process to ensure precise dimensions and to provide a high quality surface for appearance.

As with any other wood product, PSL should be protected from the weather during jobsite storage and after installation. Wrapping of the product for shipment to the job site is important in providing moisture protection. End and edge sealing of the product will enhance its resistance to moisture penetration. PSL readily accepts preservative treatment and it is possible to obtain a high degree of preservative penetration. Treated PSL can be specified in high humidity exposures.

PSL is a proprietary product and therefore, the specific engineering properties and sizes are unique to each manufacturer. Thus, PSL does not have a common standard of production and common design values. Design values are derived from test results analysed in accordance with CSA O86 and ASTM D5456 and the design values are reviewed and approved by the Canadian Construction Materials Centre (CCMC). Products meeting the CCMC guidelines receive an Evaluation Number and Evaluation Report that includes the specified design strengths, which are subsequently listed in CCMC’s Registry of Product Evaluations. The manufacturer’s name or product identification and the stress grade is marked on the material at various intervals, but due to end cutting it may not be present on every piece.

The Canadian Construction Materials Centre (CCMC) has accepted PSL for use as heavy timber construction, as described under the provisions within Part 3 of the National Building Code of Canada.

For further information, refer to the following resources:

APA – The Engineered Wood Association

Canadian Construction Materials Centre (CCMC), Institute for Research in Construction

CSA O86 Engineering design in wood

ASTM D5456 Standard Specification for Evaluation of Structural Composite Lumber Products