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Connection design variability is often considered to be a significant cost driver for mass timber projects, yet designers often lack clear guidance on what standard solutions could look like. The purpose of this document is to provide the construction industry with standardized detailing practices that cover a wide range of connections commonly found in mass timber buildings in Canada. These details can be adapted across multiple projects with various design teams and suppliers. The focus is on providing high-capacity, simple installation, and overall cost-effectiveness for timber connections. Six details are presented based on typical beam, column, and wall connections. This document also outlines the design focus areas that were prioritized during detail development. Lastly, a checklist is provided for detailers to ensure that all priorities are considered. Companion 3D versions of these details can downloaded here.

The design values for visually graded and mechanically graded Hem-Fir (N) dimension lumber have been updated in response to the routine assessment of strength and stiffness to ensure reliable performance in structural applications. The following Frequently Asked Questions provide detailed information about the updated design values, their implementation, and practical implications. This content is provided as general information only and is not intended to be relied upon for design decisions. For actual use and design implications, users of Hem-Fir (N) should consult the applicable design guides or specifications

The design values for visually graded and mechanically graded Hem-Fir (N) dimension lumber have been updated in response to the routine assessment of strength and stiffness to ensure reliable performance in structural applications. These updates take effect on April 1, 2025, and are published in the NLGA Standard Grading Rules for Canadian Lumber, CSA O86 – Engineering Design in Wood, and the National Design Specification® (NDS®) Supplement for Wood Construction, developed by the American Wood Council (AWC). Within the NDS® Supplement, these updates specifically apply to Tables 4A and 4C, with additional impacts on Table 4G. The following Frequently Asked Questions provide detailed information about the updated design values, their implementation, and practical implications. This content is provided as general information only and is not intended to be relied upon for design decisions. For actual use and design implications, users of Hem-Fir (N) should consult the applicable design guides or specifications (e.g., CSA O86 – Engineering design in wood or the National Design Specifications® (NDS).

Framing connectors are proprietary products and include fastener types such as; framing anchors, framing angles, joist, purling and beam hangers, truss plates, post caps, post anchors, sill plate anchors, steel straps and nail-on steel plates. Framing connectors are often used for different reasons, such as; their ability to provide connections within prefabricated light-frame wood trusses, their ability to resist wind uplift and seismic loads, their ability to reduce the overall depth of a floor or roof assembly, or their ability to resist higher loads than traditional nailed connections. Examples of some common framing connectors are shown in Figure 5.6, below. Framing connectors are made of sheet metal and are manufactured with pre-punched holes to accept nails. Standard framing connectors are commonly manufactured using 20- or 18-gauge zinc coated sheet steel. Medium and heavy-duty framing connectors can be made from heavier zinc-coated steel, usually 12-gauge and 7-gauge, respectively. The load transfer capacity of framing connectors is related to the thickness of the sheet metal as well as the number of nails used to fasten the framing connector to the wood member. Framing connectors are suitable for most connection geometries that use dimensional lumber that is 38 mm (2″ nom.) and thicker lumber. In light-frame wood construction, framing connectors are commonly used in connections between joists and headers; rafters and plates or ridges; purlins and trusses; and studs and sill plates. Certain types of framing connectors, manufactured to fit larger wood members and carry higher loads, are also suitable for mass timber and post and beam construction. Manufacturers of the framing connectors will specify the type and number of fasteners, along with the installation procedures that are required in order to achieve the tabulated resistance(s) of the connection. The Canadian Construction Materials Centre (CCMC), Institute for Research in Construction (IRC), produce evaluation reports that document resistance values of framing connectors, which are derived from testing results.   Figure 5.6 Framing Connectors   For more information, refer to the following resources: Canadian Construction Material Centre, National Research Council of Canada Truss Plate Institute of Canada CSA S347 Method of Test for Evaluation of Truss Plates used in Lumber Joints ASTM D1761 Standard Test Methods for Mechanical Fasteners in Wood Canadian Wood Truss Association

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

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.  

CSA O86 Engineering design in wood The National Building Code of Canada (NBC) contains requirements regarding the engineering design of structural wood products and systems. The CSA O86 standard is referenced in Part 4 of the NBC and in provincial building codes for the engineered design of structural wood products. The first edition of CSA O86 was published in 1959. CSA O86 provides criteria for the structural design and evaluation of wood structures or structural elements. It is written in the limit states design (LSD) format and provides resistance equations and specified strength values for structural wood products, including: graded lumber, glued-laminated timber, cross-laminated timber (CLT), unsanded plywood, oriented strandboard (OSB), composite building components, light-frame shearwalls and diaphragms, timber piling, pole-type construction, prefabricated wood I-joists, structural composite lumber (SCL) products, permanent wood foundations (PWF), and their structural connections. The CSA O86 provides rational approaches for structural design checks related to ultimate limit states, such as flexure, shear, and bearing, as well as serviceability limit states, such as deflection and vibration. The CSA O86 also contains strength modification factors for behaviour related to duration of load, size effects, service condition, lateral stability, system effects, preservative and fire-retardant treatment, notches, slenderness, and length of bearing. Structural design of wood buildings and components is undertaken using the loads defined in Part 4 of the NBC and the material resistance values obtained using the CSA O86 standard. Housing and other small buildings can be built without a full structural design using the prescriptive requirements outlined in Part 9 ‘Housing and Small Buildings’ of the NBC. For further information, refer to the following resources: Wood Design Manual (Canadian Wood Council) Introduction to Wood Design (Canadian Wood Council) National Building Code of Canada CSA O86 Engineering design in wood

BUILDING CODES & STANDARDS (THE REGULATORY SYSTEM) The construction industry is regulated through building codes which are informed by: Design standards that provide information on “how to” build with wood, Product standards that define the characteristics of the wood products that can be used in design standards, and Test standards that set out the methodology for establishing a wood product’s characteristics CWC is active in a technical capacity in all areas of the Regulatory System. This includes: BUILDING CODES – CWC participates extensively in the development process of the Building Codes in Canada. CWC is a member of both National and Provincial Building Code Committees. These Committees are balanced and representation is limited to about 25 members on each Committee. Competing interests (i.e. steel and concrete) sit on the same Committees. This is an arena where CWC can win or lose ground for members’ products. DESIGN STANDARDS – Each producer of structural materials develops engineering design standards that provide information on how to use their products in buildings. CWC holds the Secretariat for Canada’s wood design standard (CSA O86 “Engineering Design in Wood”), providing both technical expertise and administrative support for its development. CWC is also a member of the American Wood Council (AWC) committee that is responsible for the U.S. National Design Specification for wood design. PRODUCT STANDARDS – CWC is involved in the development of Canadian, U.S. and international standards for its wood building product producers. TEST STANDARDS – CWC is involved in developing Canadian, U.S. and international test standards in areas that affect wood products, such as fire performance. Detailed building codes & standards pages: Acoustics Combustible construction Encapsulated mass timber construction Energy Code National Fire Code National Model Codes in Canada Wood design in the National Building Code of Canada Wood in non-combustible buildings Wood Standards CSA O86 Engineering design in wood CSA S-6 Canadian Highway Bridge Design Code CSA S406 Permanent Wood Foundations CSA 080 Wood Preservation

A structure must be designed to resist all the loads expected to act on the structure during its service life. Under the effects of the expected applied loads, the structure must remain intact and perform satisfactorily. In addition, a structure must not require an inordinate amount of resources to construct. Thus, the design of a structure is a balance of necessary reliability and reasonable economy. Wood products are frequently used to provide the principal means of structural support for buildings. Economy and soundness of construction can be achieved by using wood products as members for structural applications such as joists, wall studs, rafters, beams, girders, and trusses. In addition, wood sheathing and decking products perform both a structural role by transferring wind, snow, occupant and content loads to the main structural members, as well as the function of building enclosure. Wood can be used in many structural forms such as light-frame housing and small buildings that utilize repetitive small dimension members or within larger and heavier structural framing systems, such as mass timber construction, which is often utilized for commercial, institutional or industrial projects. The engineered design of wood structural components and systems is based on the CSA O86 standard. During the 1980s, the design of wood structures in Canada, as directed by the National Building Code of Canada (NBC) and CSA O86, changed from working stress design (WSD) to limit states design (LSD), making the structural design approach for wood similar to those of other major building materials. All structural design approaches require the following for both strength and serviceability: Member resistance = Effects of design loads Using the LSD method, the structure and its individual components are characterized by their resistance to the effects of the applied loads. The NBC applies factors of safety to both the resistance side and the load side of the design equation: Factored resistance = Factored load effect The factored resistance is the product of a resistance factor (f) and the nominal resistance (specified strength), both of which are provided in CSA O86 for wood materials and connections. The resistance factor takes into account the variability of dimensions and material properties, workmanship, type of failure, and uncertainty in the prediction of resistance. The factored load effect is calculated in accordance with the NBC by multiplying the actual loads on the structure (specified loads) by load factors that account for the variability of the load. No two samples of wood or any other material are exactly the same strength. In any manufacturing process, it is necessary to recognize that each manufactured piece will be unique. Loads, such as snow and wind, are also variable. Therefore, structural design must recognize that loads and resistances are really groups of data rather than single values. Like any group of data, there are statistical attributes such as mean, standard deviation, and coefficient of variation. The goal of design is to find a reasonable balance between reliability and factors such as economy and practicality. The reliability of a structure depends on a variety of factors that can be categorized as follows: external influences such as loads and temperature change; modelling and analysis of the structure, code interpretations, design assumptions and other judgements which make up the design process; strength and consistency of materials used in construction; and quality of the construction process. The LSD approach is to provide adequate resistance to certain limit states, namely strength and serviceability. Strength limit states refer to the maximum load-carrying capacity of the structure. Serviceability limit states are those that restrict the normal use and occupancy of the structure such as excessive deflection or vibration. A structure is considered to have failed or to be unfit for use when it reaches a limit state, beyond which its performance or use is impaired. The limit states for wood design are classified into the following two categories: Ultimate limit states (ULS) are concerned with life safety and correspond to the maximum load-carrying capacity and include such failures as loss of equilibrium, loss of load-carrying capacity, instability and fracture; and Serviceability limit states (SLS) concern restrictions on the normal use of a structure. Examples of SLS include deflection, vibration and localized damage. Due to the unique natural properties of wood such as the presence of knots, wane or slope of grain, the design approach for wood requires the use of modification factors specific to the structural behaviour. These modification factors are used to adjust the specified strengths provided in CSA O86 in order to account for material characteristics specific to wood. Common modification factors used in structural wood design include duration of load effects, system effects related to repetitive members acting together, wet or dry service condition factors, effects of member size on strength, and influence of chemicals and pressure treatment Wood building systems have high strength-to-weight ratios and light-frame wood construction contains many small connectors, most commonly nails, which provide significant ductility and capacity when resisting lateral loads, such as earthquake and wind. Light-frame shearwalls and diaphragms are a very common and practical lateral bracing solution for wood buildings. Typically, the wood sheathing, most commonly plywood or oriented strand board (OSB), that is specified to resist the gravity loading can also act as the lateral force resisting system. This means that the sheathing serves a number of purposes including distributing loads to the floor or roof joists, bracing beams and studs from buckling out of plane, and providing the lateral resistance to wind and earthquake loads. Other lateral load resisting systems that are used in wood buildings include rigid frames or portal frames, knee bracing and cross-bracing. A table of typical spans is presented below to aid the designer in selecting an appropriate wood structural system.     For further information, refer to the following resources: Introduction to Wood Design (Canadian Wood Council) Wood Design Manual (Canadian Wood Council) CSA O86 Engineering design in wood National Building Code of Canada www.woodworks-software.com

It is not possible or practical to precisely predict the vertical movement of wood structures due to the many factors involved in construction. It is, however, possible to obtain a good estimate of the vertical movement to avoid structural, serviceability, and building envelope problems over the life of the structure. Typically “S-Dry” and “S-Grn” lumber will continue to lose moisture during storage, transportation and construction as the wood is kept away from liquid water sources and adapts to different atmospheric conditions. For the purpose of shrinkage prediction, it is usually customary to assume an initial moisture content (MC) of 28% for “S-Green” lumber and 19% for “S-Dry” lumber. “KD” lumber is assumed to have an initial MC of 15% in this series of fact sheets. Different from solid sawn wood products, Engineered Wood Products (EWP) are usually manufactured with MC levels close to or even lower than the equilibrium moisture content (EMC) in service. Plywood, Oriented Strand Board (OSB), Laminated Veneer Lumber (LVL), Laminated Strand Lumber (LSL), and Parallel Strand Lumber (PSL) are usually manufactured at MC levels ranging from 6% to 12%. Engineered wood I-joists are made using kiln dried lumber (usually with moisture content below 15%) or structural composite lumber (such as LVL) flanges and plywood or OSB webs, therefore they are usually drier and have lower shrinkage than typical “S-Dry” lumber floor joists. Glued-laminated timbers (Glulam) are manufactured at MC levels from 11% to 15%, so are the recently-developed Cross-laminated Timbers (CLT). For all these products, low shrinkage can be achieved and sometimes small amounts of swelling can be expected in service if their MC at manufacturing is lower than the service EMC. In order to fully benefit from using these dried products including “S-Dry” lumber and EWP products, care must be taken to prevent them from wetting such as by rain during shipment, storage and construction. EWPs may also have lower shrinkage coefficients than solid wood due to the adhesives used during manufacturing and the more mixed grain orientations in the products, including the use of cross-lamination of veneers (plywood) or lumber (CLT). The APEGBC Technical and Practice Bulletin emphasizes the use of EWP and dimension lumber with 12% moisture content for the critical horizontal members to reduce differential movement in 5 and 6-storey wood frame buildings.

Most buildings are designed to accommodate a certain range of movement. In design, it is important for designers to identify locations where potential differential movement could affect structural integrity and serviceability, predict the amount of differential movement and develop proper detailing to accommodate it. To allow non-structural materials to be appropriately constructed, estimate of anticipated differential movement should be provided in the design drawings. Simply specifying wood materials with lower MC at time of delivery does not guarantee that the wood will not get wet on construction sites and will deliver lower shrinkage amounts as anticipated. It is therefore important to ensure that wood does not experience unexpected wetting during storage, transportation and construction. Good construction sequencing also plays an important role in reducing wetting, the consequent wood shrinkage and other moisture-related issues. Existing documents such as the APEGBC Technical and Practice Bulletin on 5- and 6-Storey Wood Frame Residential Building Projects, the Best Practice Guide published by the Canadian Mortgage and Housing Corporation (CMHC), the Building Enclosure Design Guide – Wood Frame Multi-Unit Residential Buildings published by the BC Housing- Homeowner Protection Office (HPO) provide general design guidance on how to reduce and accommodate differential movement in platform frame construction.

Movement in structures due to environmental condition changes and loads must be considered in design. Temperature changes will cause movement in concrete, steel and masonry structures. For wood materials, movement is primarily related to shrinkage or swelling caused by moisture loss or gain when the moisture content is below 28% (wood fiber saturation point). Other movement in wood structures may also include: settlement (bedding-in movement) due to closing of gaps between members and deformation due to compression loads, including instantaneous elastic deformation and creep. Differential movement can occur where wood frame is connected to rigid components such as masonry cladding, concrete elevator shafts, mechanical services and plumbing, and where mixed wood products such as lumber, timbers, and engineered wood products are used. Evidence from long-term wood frame construction practices shows that for typical light frame construction up to three storeys high, differential movement can be relatively easily accommodated such as through specifying “S-Dry” lumber. However, differential movement over the height of wood-frame buildings becomes a very important consideration for taller buildings due to its cumulative effect. The APEGBC Technical and Practice Bulletin provides general design guidance and recommends the use of engineered wood products and dimension lumber with 12% moisture content for floor joists to reduce and accommodate differential movement in 5 and 6-storey wood frame buildings. Examples of differential movement concerns and solutions in wood-frame buildings can also be found in the Best Practice Guide published by the Canadian Mortgage and Housing Corporation and the Building Enclosure Design Guide –Wood Frame Multi-Unit Residential Buildings published by the Homeowner Protection Office of BC Housing. This document illustrates the causes and other basic information related to vertical movement in wood platform frame buildings and recommendations on material handling and construction sequencing to protect wood from rain and reduce the vertical movement.