**2. Lumber and lumber-based MTP**

### **2.1 Lumber**

Lumber is a manufactured product derived from logs, including boards (elements with limited thickness), dimension lumber (elements with relatively small section dimensions), and timbers (elements with relatively large section dimensions). In North America, most lumber is softwood dimension lumber having thicknesses ranging from 38 to 89 mm, widths from 38 to 184 mm, and lengths of up to about 5 m [6]. Dimension lumber is widely used in light-frame construction, which is categorized into four groups in the Canadian practice: structural light framing, structural joists and planks, light framing, and studs. Dimension lumber is usually graded by visual inspection in terms of appearance characteristics, such as knots and slope of grain. For example, the grades of dimension lumber used for structural light framing construction are Select Structural (SS), No. 1, No. 2, and No. 3. It should be noted that there is not a strength difference between No. 1 and No. 2 Canadian dimension lumber albeit there exists an appearance difference [6]. Therefore, the product mix of No. 2 and Better is commonly used where the appearance of No. 1 grade lumber is not required. Alternatively, dimension lumber can be mechanically evaluated and sorted into grades using so-called machine stressrated (MSR) lumber or machine-evaluated lumber (MEL) [6]. The MSR machine is widely used in wood industry to nondestructively test each piece of dimension lumber to determine its stiffness so that it can be assigned a permitted design stress based on the established relationship between the stiffness and bending

**11**

**Figure 3.**

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

of pounds per square inch (106

products used as studs [6].

**2.2 Glue-laminated timber (GLT or glulam)**

strength. In North America, grades of MSR lumber are assigned "f-E" values, such as 1950f-1.7E. The "f" value designates the predicted strength in pounds per square inch (psi), and the "E" value designates the average stiffness measured in millions

Boards are lumber products having thicknesses of 32 mm or less, making them usable as decking and sheathing. When the smallest cross-sectional dimension of a lumber product reaches or exceeds 140 mm it is termed timber, which is graded based on visual inspection methods [6]. Uses of dimension lumber and timbers widely range with differences in whether the former or latter is suitable depending on the type of structural system, and performance requirements applicable to a structural system. In general, dimension lumber is used in systems where multiple parallelly arranged elements act together to resist effects of particular structural design loads. Timbers, on the other hand, can be used in situations where multiple elements or a single element is designed to resist effects of particular structural design loads. Another important difference is that dimension lumber elements must always be protected from effects of design fire situations; whereas, depending on

psi) [6].

specifics of a situation, timbers may not require such protection.

Finger-joints are commonly used to join short pieces of lumber together to make longer pieces. Meshing wedges known as "fingers" are made as either side of a joint, as illustrated in **Figure 3**, and bonded using structural adhesive. The joint profile governs the strength of a joint, and is defined by the finger length, tip thickness, tip gap, and finger pitch, slope, and depth. For example, a 29-mm-long finger joint is commonly used (**Figure 3**—left). However, reducing finger length to 13 mm with some modifications to the joint profile (**Figure 3**—right) not only helps to reduce material waste, but also keeps the same or slightly higher strength joints [8]. Also, it is noted that cutting out strength reducing features like large knots then finger joining lumber is a highly effective way of upgrading properties of dimension lumber, increasing value, and enabling higher value uses like creation of high-performance MTP [6]. Another advantage of finger joining lumber is that it increases dimensional stability under changing environmental conditions prior to or after installation of lumber in structures. Adhesives used in finger-joints are usually phenol-resorcinol formaldehyde for lumber products intended for general applications or incorporated in GLT elements, or polyvinyl acetate for lumber

GLT (also widely known as glulam) is a structural product composed of multiple pieces of finger-joined dimension lumber, or other types of EWP, adhesively face-toface bonded to create a desired form. GLT was first used in Europe in the early 1890s. A 1901 patent from Switzerland signaled the true beginning of GLT construction [9]. A significant development in the GLT industry was the introduction of fully

*Two finger joint profiles (left: 29-mm long; right: 13-mm long) used for joining short pieces of lumber.*

*Timber Buildings and Sustainability*

of the studs [7].

and occupants.

**2.1 Lumber**

**2. Lumber and lumber-based MTP**

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

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

Lumber is a manufactured product derived from logs, including boards (elements with limited thickness), dimension lumber (elements with relatively small section dimensions), and timbers (elements with relatively large section dimensions). In North America, most lumber is softwood dimension lumber having thicknesses ranging from 38 to 89 mm, widths from 38 to 184 mm, and lengths of up to about 5 m [6]. Dimension lumber is widely used in light-frame construction, which is categorized into four groups in the Canadian practice: structural light framing, structural joists and planks, light framing, and studs. Dimension lumber is usually graded by visual inspection in terms of appearance characteristics, such as knots and slope of grain. For example, the grades of dimension lumber used for structural light framing construction are Select Structural (SS), No. 1, No. 2, and No. 3. It should be noted that there is not a strength difference between No. 1 and No. 2 Canadian dimension lumber albeit there exists an appearance difference [6]. Therefore, the product mix of No. 2 and Better is commonly used where the appearance of No. 1 grade lumber is not required. Alternatively, dimension lumber can be mechanically evaluated and sorted into grades using so-called machine stressrated (MSR) lumber or machine-evaluated lumber (MEL) [6]. The MSR machine is widely used in wood industry to nondestructively test each piece of dimension lumber to determine its stiffness so that it can be assigned a permitted design stress based on the established relationship between the stiffness and bending

**10**

strength. In North America, grades of MSR lumber are assigned "f-E" values, such as 1950f-1.7E. The "f" value designates the predicted strength in pounds per square inch (psi), and the "E" value designates the average stiffness measured in millions of pounds per square inch (106 psi) [6].

Boards are lumber products having thicknesses of 32 mm or less, making them usable as decking and sheathing. When the smallest cross-sectional dimension of a lumber product reaches or exceeds 140 mm it is termed timber, which is graded based on visual inspection methods [6]. Uses of dimension lumber and timbers widely range with differences in whether the former or latter is suitable depending on the type of structural system, and performance requirements applicable to a structural system. In general, dimension lumber is used in systems where multiple parallelly arranged elements act together to resist effects of particular structural design loads. Timbers, on the other hand, can be used in situations where multiple elements or a single element is designed to resist effects of particular structural design loads. Another important difference is that dimension lumber elements must always be protected from effects of design fire situations; whereas, depending on specifics of a situation, timbers may not require such protection.

Finger-joints are commonly used to join short pieces of lumber together to make longer pieces. Meshing wedges known as "fingers" are made as either side of a joint, as illustrated in **Figure 3**, and bonded using structural adhesive. The joint profile governs the strength of a joint, and is defined by the finger length, tip thickness, tip gap, and finger pitch, slope, and depth. For example, a 29-mm-long finger joint is commonly used (**Figure 3**—left). However, reducing finger length to 13 mm with some modifications to the joint profile (**Figure 3**—right) not only helps to reduce material waste, but also keeps the same or slightly higher strength joints [8]. Also, it is noted that cutting out strength reducing features like large knots then finger joining lumber is a highly effective way of upgrading properties of dimension lumber, increasing value, and enabling higher value uses like creation of high-performance MTP [6]. Another advantage of finger joining lumber is that it increases dimensional stability under changing environmental conditions prior to or after installation of lumber in structures. Adhesives used in finger-joints are usually phenol-resorcinol formaldehyde for lumber products intended for general applications or incorporated in GLT elements, or polyvinyl acetate for lumber products used as studs [6].
