Mass Timber
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.
Light-frame Trusses
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
Lumber
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 Checking and splitting Checking occurs when lumber is rapidly dried. The surface dries quickly, while the core remains at a higher moisture content for some time. As a result, the surface attempts to shrink but is restrained by the core. This restraint causes tensile stresses at the surface, which if large enough, can pull the fibres apart, thereby creating a check. Splits are through checks that generally occur at the end of wood members. When a wood member dries, moisture is lost very rapidly from the end of the member. At midlength, however, the wood is still at a higher moisture content. This difference in moisture content creates tensile stresses at the end of the member. When the stresses exceed the strength of the wood, a split is formed. Large dimension solid sawn timbers are susceptible to checking and splitting since they are always dressed green (S-Grn). Furthermore, due to their large size, the core dries slowly and the tensile stresses at the surface and at the ends can be large. Minor checks confined to the surface areas of a wood member very rarely have any effect on the strength of the member. Deep checks could be significant if they occur at a point of high shear stress. Checks in columns are not of structural importance, unless the check develops into a through split that will increase the slenderness ratio of the column. The specified shear strengths of dimension lumber and timbers have been developed to consider the maximum amount of checking or splitting permitted by the applicable grading rule. The possibility and severity of splitting and checking can be reduced by controlling the rate at which drying occurs. This may be done by keeping wood out of direct sunlight and away from any artificial heat sources. Furthermore, the ends may be coated with an end sealer to retard moisture loss. Other actions which will minimize dimension change and the possibility of checking or splitting are: specifying wood products that are as close as possible in moisture content to the expected equilibrium moisture content of the end use ensuring dry wood products are protected by proper storage and handling Fingerjoined lumber Fingerjoined products are manufactured by taking shorter pieces of kiln-dried lumber, machining a ‘finger’ profile in each end of the short-length pieces, adding an appropriate structural adhesive, and end-gluing the pieces together to make a longer length piece of lumber. The length of a fingerjoined lumber is not limited by the length of the log. In fact, the manufacturing process can result in the production of joists and rafters in lengths of 12 m (40 ft) or more. The process of fingerjoining is also used within the manufacturing process for several other engineered wood products, including glued-laminated timber and wood I-joists. The specific term “fingerjoined lumber” applies to dimension lumber that contains finger joints. Fingerjoining derives greater value from the forest resource by using short length pieces of lower grade lumber as input for the manufacture of a value-added engineered wood product. The fingerjoining process utilizes short off cut pieces of lumber and results in more efficient use of the harvested wood fibre. Fingerjoined lumber can be manufactured from any commercial species or species group. The most commonly used species group from which fingerjoined lumber is produced is Spruce-Pine-Fir (S-P-F). Design advantages of fingerjoined lumber Fingerjoined lumber is an engineered wood product that is desirable for several reasons: straightness dimensional stability interchangeability with non-fingerjointed lumber highly efficient use of wood fibre The design and performance advantages of this engineered wood product are its straightness and dimensional stability. The straightness and dimensional stability of fingerjoined lumber is a result of short length pieces of lumber, consisting of relatively straight grain and fewer natural defects, being combined with one another to form a longer length piece of lumber. The grain pattern along fingerjoined lumber becomes non-uniform and random by attaching many short pieces together. This results in fingerjoined lumber being less prone to warping than solid sawn lumber. The fingerjoining process also results in the reduction or removal of strength reducing defects, producing a structural wood product with less variable engineering properties than solid sawn dimensional lumber. The most common use of finger-joined lumber is as studs in shearwalls and vertical load bearing walls. The most important factor for studs is straightness. Fingerjoined studs will stay straighter than solid sawn dimensional lumber studs when subjected to changes in temperature and humidity. This feature results in significant benefits to the builder and homeowner including a superior building, the elimination of nail pops in drywall and other problems related to dimensional changes.
Connections
As for all other building materials, a critical aspect of wood structures is the manner by which members are connected. Wood products are building materials which are easily drilled, chiseled, or otherwise shaped to facilitate the connection of members, and a number of methods and a wide range of products are available for connecting wood. The installation of metal fasteners is the most common method of connecting wood products and a wide range of hardware is available. These range from the nails and the light connectors used for light framing construction to the bolts, side plates and other hardware used for heavy member connections. Each type of fastener is designed to be used with a particular type of construction. For many applications, such as nailing for light-frame wall construction, metal fasteners serve only a structural purpose, and will be hidden from view by interior and exterior finishes. In other cases where wood members serve a structural purpose and are left exposed to add visual interest to a design and give a robust appearance to a structure, thought must be given to the connection layout and the selection and finishing of the wood products themselves. In other instances, where metal fasteners are exposed to view, the designer might want them to be as inconspicuous as possible. This can be done by selecting fasteners such as split rings and bolts, by reducing the visual impact of hardware through recessing it within the wood members, or by using painting to reduce the prominence of a connection.
i -Joists
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
Panel Products
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.
Laminate Veneer Lumber
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
Acoustics
Wood is composed of many small cellular tubes that are predominantly filled with air. The natural composition of the material allows for wood to act as an effective acoustical insulator and provides it with the ability to dampen vibrations. These sound-dampening characteristics allow for wood construction elements to be specified where sound insulation or amplification is required, such as libraries and auditoriums. Another important acoustical property of wood is its ability to limit impact noise transmission, an issue commonly associated with harder, more dense materials and construction systems. The use of topping or a built-up floating floor system overlaid on light wood frame or mass timber structural elements is a common approach to address acoustic separation between floors of a building. Depending on the type of materials in the built-up floor system, the topping can be applied directly to the wood structural members or over top of a moisture barrier or resilient layer. The use of gypsum board, absorptive (batt/loose-fill) insulation and resilient channels are also critical components of a wood-frame wall or floor assembly that also contribute to the acoustical performance of the overall assembly. Acoustic design considers a number of factors, including building location and orientation, as well as the insulation or separation of noise-producing functions and building elements. Sound Transmission Class (STC), Apparent Sound Transmission Class (ASTC) and Impact Insulation Class (IIC) ratings are used to establish the level of acoustic performance of building products and systems. The different ratings can be determined on the basis of standardized laboratory testing or, in the case of ASTC ratings, calculated using methodologies described in the NBC. Currently, the National Building Code of Canada (NBC) only regulates the acoustical design of interior wall and floor assemblies that separate dwelling units (e.g. apartments, houses, hotel rooms) from other units or other spaces in a building. The STC rating requirements for interior wall and floor assemblies are intended to limit the transmission of airborne noise between spaces. The NBC does not mandate any requirements for the control of impact noise transmission through floor assemblies. Footsteps and other impacts can cause severe annoyance in multifamily residences. Builders concerned about quality and reducing occupant complaints will ensure that floors are designed to minimize impact transmission. Beyond conforming to the minimum requirements of the NBC in residential occupancies, designers can also establish acoustic ratings for design of non-residential projects and specify materials and systems to ensure the building performs at that level. In addition to limiting transmission of airborne noise through internal structural walls and floors, flanking transmission of sound through perimeter joints and sound transmission through non-structural partition walls should also be considered during the acoustical design. Further information and requirements related to STC, ASTC and IIC ratings are provided in Appendix A of the NBC in sections A-9.10.3.1. and A-9.11.. This includes, inter alia, Tables 9.10.3.1-A and 9.10.3.1.-B that provide generic data on the STC ratings of different types of wood stud walls and STC and IIC ratings for different types of wood floor assemblies, respectively. Tables A-9.11.1.4.-A to A-9.11.1.4.-D present generic options for the design and construction of junctions between separating and flanking assemblies. Constructing according to these options is likely to meet or exceed an ASTC rating of 47 that is mandated by the NBC. Table A-Table 9.11.1.4. presents data about generic floor treatments that can be used to improve the flanking sound insulation performance of lightweight framed floors, i.e., additional layers of material over the subfloor (e.g. concrete topping, OSB or plywood) and finished flooring or coverings (e.g., carpet, engineered wood).
Combustible construction
The provision of fire safety in a building is a complex matter; far more complex than the relative combustibility of the main structural materials used in a building. To develop safe code provisions, prevention, suppression, movement of occupants, mobility of occupants, building use, and fuel control are but a few of the factors that must be considered in addition to the combustibility of the structural components. Fire-loss experience shows that building contents play a large role in terms of fuel load and smoke generation potential in a fire. The passive fire protection provided by the fire-resistance ratings on the floor and wall assemblies in a building assures structural stability in a fire. However, the fire-resistance rating of the structural assemblies does not necessarily control the movement of smoke and heat, which can have a large impact on the level of safety and property damage resulting from fire. The National Building Code of Canada (NBC) categorizes wood buildings as ‘combustible construction’. Despite being termed combustible, common construction techniques can give wood frame construction fire-resistance ratings up to two hours. When designed and built to code requirements, wood buildings provide the same level of life safety and property protection required for comparably sized buildings defined under the NBC as ‘noncombustible construction’. Wood has been used for virtually all types of buildings, including; schools, warehouses, fire stations, apartment buildings, and research facilities. The NBC sets out guidelines for the use of wood in applications that extend well beyond the traditional residential and small building sector. The NBC allows wood construction of up to six storeys in height, and wood cladding for buildings designated to be of noncombustible construction. When meeting the area and height limits for the various NBC building categories, wood frame construction can meet the life safety requirements by making use of wood-frame assemblies (usually protected by gypsum wallboard) that are tested for fire-resistance ratings. The allowable height and area restrictions can be extended by using fire walls to break a large building area into smaller separate building areas. The recognized positive contribution to both life safety and property protection which comes from the use of automatic sprinkler systems can also be used to increase the permissible area of wood buildings. Sprinklers typically operate very early in a fire thereby quickly controlling the damaging effects. For this reason, the provision of automatic sprinkler protection within a building greatly improves the life safety and property protection prospects of all buildings including those constructed of noncombustible materials. The NBC permits the use of ‘heavy timber construction’ in buildings where combustible construction is required to have a 45-minute fire-resistance rating. This form of heavy timber construction is also permitted to be used in large noncombustible buildings in certain occupancies. To be acceptable, the components must comply with minimum dimension and installation requirements. Heavy timber construction is afforded this recognition because of its performance record under actual fire exposure and its acceptance as a fire-safe method of construction. In sprinklered buildings permitted to be of combustible construction, no fire-resistance rating is required for the roof assembly or its supports when constructed from heavy timber. In these cases, a heavy timber roof assembly and its supports would not have to conform to the minimum member dimensions stipulated in the NBC. Mass timber elements may also be used whenever combustible construction is permitted. In those instances, however, such mass timber elements need to be specifically designed to meet any required fire-resistance ratings. NBC definitions: Combustible means that a material fails to meet the acceptance criteria of CAN/ULC-S114, “Test for Determination of Non-Combustibility in Building Materials.” Combustible construction means that type of construction that does not meet the requirements for noncombustible construction. Heavy timber construction means that type of combustible construction in which a degree of fire safety is attained by placing limitations on the sizes of wood structural members and on thickness and composition of wood floors and roofs and by the avoidance of concealed spaces under floors and roofs. Noncombustible construction means that type of construction in which a degree of fire safety is attained by the use of noncombustible materials for structural members and other building assemblies. Noncombustible means that a material meets the acceptance criteria of CAN/ULC-S114, “Test for Determination of Non-Combustibility in Building Materials.” For further information, refer to the following resources: National Building Code of Canada CAN/ULC-S114 Test for Determination of Non-Combustibility in Building Materials Wood Design Manual 2017
Encapsulated mass timber construction
In addition to combustible, heavy timber and noncombustible construction, a new construction type is presently being considered for inclusion into the National Building Code of Canada (NBC). Encapsulated mass timber construction (EMTC) is proposed to be defined as the “type of construction in which a degree of fire safety is attained by the use of encapsulated mass timber elements with an encapsulation rating and minimum dimensions for the structural timber members and other building assemblies.” EMTC is neither ‘combustible construction’ nor ‘heavy timber construction’ nor ‘noncombustible construction’, as defined within the NBC. EMTC is required to have an encapsulation rating. The encapsulation rating is the time, in minutes, that a material or assembly of materials will delay the ignition and combustion of encapsulated mass timber elements when it is exposed to fire under specified conditions of test and performance criteria, or as otherwise prescribed by the NBC. The encapsulation rating for EMTC is determined through the ULC S146 test method. In order for structural wood elements to be considered ‘mass timber’, they must meet minimum size requirements, which are different for horizontal (walls, floors, roofs, beams) and vertical (columns, arches) load-bearing elements and dependent on the number of sides that the element is exposed to fire. EMTC construction in Canada is expected to be limited to a height of twelve-storeys, that is, the uppermost floor level may be a maximum of 42 m (137 ft) above the first floor. An EMTC building must be sprinklered throughout according to NFPA 13 and it is likely that some mass timber will also be able to be exposed in the suites. All EMTC elements are expected to have a minimum two-hour fire resistance rating and the building floor area to be limited to 6,000 m2 for Group C occupancy and 7,200 m2 for Group D occupancy. There are restrictions on the use of exterior cladding elements in EMTC, as well as other restrictions on the use of; combustible roofing materials, combustible window sashes and frames, combustible components in exterior walls, nailing elements, combustible flooring elements, combustible stairs, combustible interior finishes, combustible elements in partitions, and concealed spaces. If any encapsulation material is damaged or removed, it will be required to be repaired or replaced so that the encapsulation rating of the materials is maintained. Additionally, requirements related to construction site fire safety are to be applied to construction access, standpipe installation and protective encapsulation. EMTC and its related provisions are anticipated to be included in the NBC 2020. NBC definitions: Combustible means that a material fails to meet the acceptance criteria of CAN/ULC-S114, “Test for Determination of Non-Combustibility in Building Materials.” Combustible construction means that type of construction that does not meet the requirements for noncombustible construction. Heavy timber construction means that type of combustible construction in which a degree of fire safety is attained by placing limitations on the sizes of wood structural members and on thickness and composition of wood floors and roofs and by the avoidance of concealed spaces under floors and roofs. Noncombustible construction means that type of construction in which a degree of fire safety is attained by the use of noncombustible materials for structural members and other building assemblies. Noncombustible means that a material meets the acceptance criteria of CAN/ULC-S114, “Test for Determination of Non-Combustibility in Building Materials.” For further information, refer to the following resources: Guide to Encapsulated Mass Timber Construction in the Ontario Building Code ULC S146 Standard Method of Test for the Evaluation of Encapsulation Materials and Assemblies of Materials for the Protection of Mass Timber Structural Members and Assemblies Fire performance of mass-timber encapsulation methods and the effect of encapsulation on char rate of cross-laminated timber (Hasburgh et al., 2016) CAN/ULC-S114 Test for Determination of Non-Combustibility in Building Materials NFPA 13 Standard for the Installation of Sprinkler Systems
Tall Wood Buildings
With advanced construction technologies and modern mass timber products such as glued-laminated timber, cross-laminated timber and structural composite lumber, building tall with wood is not only achievable but already underway – with completed contemporary buildings in Australia, Austria, Switzerland, Germany, Norway and the United Kingdom at 9 storeys and taller. Increasingly recognized by the construction sector as an important, new, and safe construction choice, the reduced carbon footprint and embodied / operational energy performance of these buildings is appealing to communities that are committed to sustainable development and climate change mitigation. Tall wood buildings, built with renewable wood products from sustainably managed forests, have the potential to revolutionize a construction industry increasingly focused on being part of the solution when it comes to urban intensification and environmental impact reduction. The Canadian wood product industry is committed to building on its natural advantage, through the development and demonstration of continuously improving wood-based building products and building systems. A tall wood building is a building over six-storeys in height (top floor is higher than 18 m above grade) that utilizes mass timber elements as a functional component of its structural support system. With advanced construction technologies and modern mass timber products such as glued-laminated timber (glulam), cross-laminated timber (CLT) and structural composite lumber (SCL), building tall with wood is not only achievable but already underway – with completed contemporary buildings in Canada, US, Australia, Austria, Switzerland, Germany, Norway, Sweden, Italy and the United Kingdom at seven-storeys and taller. Tall wood buildings incorporate modern fire suppression and protection systems, along with new technologies for acoustic and thermal performance. Tall wood buildings are commonly employed for residential, commercial and institutional occupancies. Mass timber offers advantages such as improved dimensional stability and better fire performance during construction and occupancy. These new products are also prefabricated and offer tremendous opportunities to improve the speed of erection and quality of construction. Some significant advantages of tall wood buildings include: the ability to build higher in areas of poor soils, as the super structure and foundations are lighter compared to other building materials; quieter to build on site, which means neighbours are less likely to complain and workers are not exposed to high levels of noise; worker safety during construction can be improved with the ability to work off large mass timber floor plates; prefabricated components manufactured to tight tolerances can reduce the duration of construction; tight tolerances in the building structure and building envelope coupled with energy modelling can produce buildings with high operational energy performance, increased air tightness, better indoor air quality and improved human comfort Design criteria for tall wood buildings that should be considered include: an integrated design, approvals and construction strategy, differential shrinkage between dissimilar materials, acoustic performance, behaviour under wind and seismic loads, fire performance (e.g., encapsulating the mass timber elements using gypsum), durability, and construction sequencing to reduce the exposure of wood to the elements. It is important to ensure early involvement by a mass timber supplier that can provide design assistance services that can further reduce manufacturing costs through the optimization of the entire building system and not just individual elements. Even small contributions, in connection designs for example, can make a difference to the speed of erection and overall cost. In addition, mechanical and electrical trades should be invited in a design-assist role at the outset of the project. This allows for a more complete virtual model, additional prefabrication opportunities and quicker installation. Recent case studies of modern tall wood buildings in Canada and around the world showcase the fact that wood is a viable solution for attaining a safe, cost-effective and high-performance tall building. For more information, refer to the following case studies and references: Brock Commons Tall Wood House (Canadian Wood Council) Origine Point-aux-Lievres Ecocondos,Quebec City (Cecobois) Wood Innovation and Design Centre (Canadian Wood Council) Technical Guide for the Design and Construction of Tall Wood Buildings in Canada (FPInnovations) Ontario’s Tall Wood Building Reference (Ministry of Natural Resources and Forestry & Ministry of Municipal Affairs) Summary Report: Survey of International Tall Wood Buildings (Forestry Innovation Investment & Binational Softwood Lumber Council) www.thinkwood.com/building-better/taller-buildings
Mid-Rise Buildings
When it comes to wood construction, many people think of basic 2×4 framing, panels or flooring for single-family homes. However, advances in wood science and building technology have resulted in stronger, more sophisticated and robust products that are expanding the options for wood construction, and providing more choices for builders and architects. The Canadian Wood Council’s support for mid-rise construction is not unique In Ontario, Home Builders, through organizations such as RESCON, BILD and the Ontario Home Builders Association are also highlighting this opportunity. Mid-rise buildings made of wood are a new construction option for builders. That’s good news for main-street Canada, where land is so expensive. The net benefit of reduced construction costs is increased affordability for home buyers. In terms of new economic opportunity, the ability to move forward “now” creates new construction jobs in cities and supports employment in forestry communities. This also offers increased export opportunities for current and innovative wood products, where adoption in Canada provides the example for other countries. This also reflects a new standard of engineering in that structural, fire and seismic concerns have all been addressed by the expert committees of the Canadian Commission on Building and Fire Codes. In the end, when occupied, mid-rise buildings fully meet the same requirements of the Building Code as any other type of construction from the perspective of health, safety and accessibility.
