Lumber-Based Mass Timber Products in Construction

*Meng Gong*

## **Abstract**

This chapter provides information related to commonly used wood construction methods (i.e., light-frame, post-and-beam, and mass timber) and mass timber products. It briefly discusses the manufacturing of four major lumber-based mass timber products (i.e., glue-laminated timber, nail-laminated timber, dowel-laminated timber, and cross-laminated timber), and their available dimensions and typical applications. The discussion also addresses primary lumber products, such as dimension lumber, machine stress-rated lumber, and finger-joined lumber, which are the building blocks from which mass timber products are manufactured. Advantages of using wood in construction are illustrated by examples largely from North American practices. The life cycle assessment concept is also introduced.

**Keywords:** building materials, cross-laminated timber, dowel-laminated timber, glue-laminated timber, life cycle assessment, lumber, mass timber products, nail-laminated timber, timber, wood construction

#### **1. Introduction**

Prior to the availability of rolled steel and reinforced concrete, wood was the primary structural material in North America and other timber-rich regions of the world [1]. However, the raw material resources keep changing in more recent times, e.g. log diameters become smaller and trees come from faster growing plantation species. As a result, traditional solid timber products have been supplemented by Engineered Wood Products (EWP) like glue-laminated timber (GLT or glulam), laminated veneer lumber (LVL), and oriented strand board (OSB). This has permitted economic construction of residential and nonresidential buildings, bridges, and industrial structures. Presently, using of traditional wood products and EWP is recognized as a "green" option, and is encouraged by governments as part of sustainable development and climate change mitigation strategies [2].

From a technical perspective, modern EWP commonly provide better and more predictable physical and mechanical properties than traditional wood products, such as more uniform structure, greater dimensional stability, greater strength, and stiffness. Initially, much development of EWP was focused on creating substitute products capable of replacing small dimension sawn lumber and boards as primary elements in light-frame building superstructures; but in recent decades, much attention has been switched to creation of mass timber products (MTP). The term MTP describes a family of EWP of large section size that offers the construction industry a viable alternative to use structural steel and reinforced concrete [3]. This

includes thick-panel products, such as cross-laminated timber (CLT) and structural composite lumber (SCL), as well as adhesively or mechanically laminated linear elements like GLT, nail-laminated timber (NLT), and dowel-laminated timber (DLT).

SCL refers to products manufactured by layering dried and graded wood veneers or strands bonded together by moisture-resistant adhesive into panel-like products of a width of up to 2.44 m, a thickness of 38 mm, or more. In principle, SCL is only limited in width and length by transportation considerations. SCL basically includes LVL, laminated strand lumber (LSL) and oriented strand lumber (OSL), which is usually sawn into lumber-like products. However, parallel stand lumber (PSL) is also deemed as a SCL product, which is commonly used as columns connected to other MTP. Use of terms in the literature can be colloquial, with timber-concrete composite (TCC) and other hybrid elements sometimes grouped into the meaning of MTP. Overall, MTP offers architects and builders many opportunities to express their concepts creatively, while satisfying various technical performance requirements applicable to engineered structures of many types [4]. This chapter places emphasis on the types of lumber-based MTP illustrated in **Figure 1**.

**Figure 2** illustrates three types of wood construction methods, namely light-frame, post-and-beam, and mass timber. Light-frame construction consists of studs, joists, and other framing at spacings of 600 mm or less [6], **Figure 2**—top. Dimension lumber is used for framing members and plywood or OSB for sheathing materials. Light-frame construction is an economical choice for the construction of low- and mid-rise buildings, which makes use of dimension lumber in a range of grades and dimensions [7]. Light-frame wood structures can be also used for shopping centers, plazas, service and maintenance buildings, and institutional and municipal facilities. Prefabrication of components such as wall and roof panels, even complete homes or office units are efficient extensions of this framing technique [7]. However, the structural system of a light-frame building is not well-defined, resulting in much redundancy. Design of a light-frame building often only includes architects unless the building is large.

Post-and-beam construction is a skeletal framework of posts, beams, and decking supported on a foundation, in which the posts and beams are well spaced apart, more

**9**

**Figure 2.**

*Lumber-Based Mass Timber Products in Construction DOI: http://dx.doi.org/10.5772/intechopen.85808*

than 600 mm, but commonly 1200 mm or more [6], **Figure 2**—center. Traditionally, posts and beams were made of large solid timbers, which were connected with mortise and tenon joints locked into place with hardwood pegs, with diagonal braces for stabilization of a structure [7]. Nowadays, many types of EWPs (such as GLT and LVL) and connectors (such as metal brackets, shear plates, and split rings with bolts) are very often used. The post-and-beam construction is commonly used to construct custom-designed homes, commercial buildings, recreation centers, and industrial structures, for reasons of ease of fabrication and consequent economy [7]. Unlike the light-frame construction, the structural system of a post-and-beam building is

*Wood building construction methods. Top: Light-frame construction (Source: Photo obtained from Okoye et al. [5]). Center: Post-and-beam construction (Source: Photo obtained from Post & Beam Homes). Bottom: Mass* 

*timber construction (Source: Photo obtained from UBC Public Affairs).*

**Figure 1.** *Lumber-based MTP (Source: Images obtained from StructureCraft).*

*Lumber-Based Mass Timber Products in Construction DOI: http://dx.doi.org/10.5772/intechopen.85808*

*Timber Buildings and Sustainability*

includes thick-panel products, such as cross-laminated timber (CLT) and structural composite lumber (SCL), as well as adhesively or mechanically laminated linear elements like GLT, nail-laminated timber (NLT), and dowel-laminated timber (DLT). SCL refers to products manufactured by layering dried and graded wood veneers or strands bonded together by moisture-resistant adhesive into panel-like products of a width of up to 2.44 m, a thickness of 38 mm, or more. In principle, SCL is only limited in width and length by transportation considerations. SCL basically includes LVL, laminated strand lumber (LSL) and oriented strand lumber (OSL), which is usually sawn into lumber-like products. However, parallel stand lumber (PSL) is also deemed as a SCL product, which is commonly used as columns connected to other MTP. Use of terms in the literature can be colloquial, with timber-concrete composite (TCC) and other hybrid elements sometimes grouped into the meaning of MTP. Overall, MTP offers architects and builders many opportunities to express their concepts creatively, while satisfying various technical performance requirements applicable to engineered structures of many types [4]. This chapter places

emphasis on the types of lumber-based MTP illustrated in **Figure 1**.

**Figure 2** illustrates three types of wood construction methods, namely light-frame, post-and-beam, and mass timber. Light-frame construction consists of studs, joists, and other framing at spacings of 600 mm or less [6], **Figure 2**—top. Dimension lumber is used for framing members and plywood or OSB for sheathing materials. Light-frame construction is an economical choice for the construction of low- and mid-rise buildings, which makes use of dimension lumber in a range of grades and dimensions [7]. Light-frame wood structures can be also used for shopping centers, plazas, service and maintenance buildings, and institutional and municipal facilities. Prefabrication of components such as wall and roof panels, even complete homes or office units are efficient extensions of this framing technique [7]. However, the structural system of a light-frame building is not well-defined, resulting in much redundancy. Design of a light-frame building often only includes architects unless the building is large.

Post-and-beam construction is a skeletal framework of posts, beams, and decking supported on a foundation, in which the posts and beams are well spaced apart, more

**8**

**Figure 1.**

*Lumber-based MTP (Source: Images obtained from StructureCraft).*

#### **Figure 2.**

*Wood building construction methods. Top: Light-frame construction (Source: Photo obtained from Okoye et al. [5]). Center: Post-and-beam construction (Source: Photo obtained from Post & Beam Homes). Bottom: Mass timber construction (Source: Photo obtained from UBC Public Affairs).*

than 600 mm, but commonly 1200 mm or more [6], **Figure 2**—center. Traditionally, posts and beams were made of large solid timbers, which were connected with mortise and tenon joints locked into place with hardwood pegs, with diagonal braces for stabilization of a structure [7]. Nowadays, many types of EWPs (such as GLT and LVL) and connectors (such as metal brackets, shear plates, and split rings with bolts) are very often used. The post-and-beam construction is commonly used to construct custom-designed homes, commercial buildings, recreation centers, and industrial structures, for reasons of ease of fabrication and consequent economy [7]. Unlike the light-frame construction, the structural system of a post-and-beam building is

well-defined and engineered, generating very limited or no redundancy. Design of a post-and-beam building is usually formal, involving both architects and engineers, especially if the building is relatively large. Hybrid post-and-beam and light-frame construction features the exposed heavy timber components, but allows insulation to be placed in the wall space, with finishes applied to both the inner and outer faces of the studs [7].

Mass timber construction complements traditional light-frame and post-and-beam construction methods due to emergence of various types of MTPs, **Figure 2**—bottom. It creates single or multiple material hybrid superstructures for building and other structures. Since beams are not always required, new technology and terminology, such as post-and-panel construction, have emerged. This demonstrates that MTPs have been developed into material options, where the only limits on their uses are limitations of the inventiveness of minds of architects and engineers within the scope of what applicable building/construction regulations permit [4]. What codes and standards permit architects and engineers to do is not yet uniform; but in the broad sense, construction codes and standards in various countries have transitioned, or are transitioning, away from prescriptive provisions to performance-based provisions in a manner that enables greater use of EWP, including MTP. Most important in this respect is the revision of fire performance provisions related to buildings [4, 6]. Mass timber systems are widely reported to be cost-competitive, carbon-efficient, sustainable and reliable, which stem from the scientific data generated from full-scale fire, seismic, durability, acoustic, and vibration tests being conducted internationally by researchers and engineers [3, 4]. It is now reasonable to claim that the use of EWP and MTP has the same level of supporting technical understanding as that underpinning any other major class of construction material. Latter sections of this chapter demonstrate the use of MTP as parts of high-performance buildings meeting needs of society and occupants.
