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Fasteners, Connectors and Flashing for Wood Treated With Copper-Based Preservatives The presence of moisture is a precondition for corrosion of metals. Treated wood is typically used in applications where it may be exposed to moisture for considerable periods so any fasteners and connectors used with treated wood must also be resistant to these conditions.  In addition, most wood preservatives designed for exterior use contain copper that may react with the metals used to fabricate fasteners and connectors therefore, it is important to use the right type of fastener and/or connectors. Where treated wood is used in dry environments to prevent damage by wood-destroying insects, including termites, corrosion is of less concern. Users and specifiers should also be aware that corrosive industrial, or salt air, environments may also require the use of appropriate corrosion resistant metals. Types of Wood Preserving Treatments Most copper-based preservatives are corrosive to unprotected fasteners and connectors. More recent systems such as MCA where the copper isn’t introduced in an ionic salt form, are designed to reduce the corrosion of metals, and the preserved wood is approved for use in contact with aluminum (e.g. brackets or outdoor furniture legs). Borate treatments do not increase the risk of corrosion. Recommendations on Connectors for Treated Wood Connectors used for wood treated with a copper-based preservative must be manufactured from steel either hot–dipped galvanized in accordance with ASTM A653 or hot dipped galvanized after manufacture in accordance with ASTM A123.  Galvanizing nails and screws is actually a sacrificial coating to protect the structural integrity of the fastener, and the presence of some white corrosion product on the surface is normal. Red rust appearing is an indicator of coating failure. The service life of these components can be extended by using a barrier membrane between the connector and the treated wood surface. Stainless steel connectors (type 304 or 316) should be used for maximum service life, for high preservative retentions (i.e. ground contact products) or severe applications such as salt spray environments.  For borate-treated wood used inside buildings, the same connectors can be used as for untreated wood. Recommendations on Fasteners for Treated Wood Fasteners for use in treated wood that will be exposed to the weather should be selected to withstand weathering as long as the treated wood itself.  As a minimum, nails for wood treated with a copper-based preservative must be hot-dipped galvanized in accordance with ASTM A153. Hot-dipped galvanized nails should not be fastened using a high pressure nail gun due to the risk of damage to the coating during firing. The protective coating on electroplated galvanized fasteners is too thin and will perform poorly, and common nails will corrode rapidly after fastening most copper-based treated wood.  Stainless steel should be used for maximum service life, for high preservative retentions or severe applications such as salt spray environments. Where appropriate, copper fasteners may also be used. Fasteners used in combination with metal connectors must be the same type of metal to avoid galvanic corrosion caused by dissimilar metals.  For example stainless steel fasteners should not be used in combination with galvanized connectors. Screws intended for use on wood treated with a copper-based preservative must be hot dipped galvanized in accordance with ASTM A153 or, if recommended by the manufacturer and the preservative supplier, high-quality polymer coated. Stainless steel should be used for maximum service life, for high preservative retentions or severe applications such as salt spray environments. For borate treated wood used inside buildings, the same fasteners can be used as for untreated wood. As a general rule aluminum fasteners should not be used with treated wood, except new generation products (MCA treated) specifically tested, approved and labelled as suitable for contact with Aluminum.  Recommendations on Flashing for Treated Wood Flashing used in contact with treated wood must be compatible with the treated wood and be last long enough to be suitable for the intended application.  Flashing must also be of the same type of metal as any fasteners that penetrate through them to avoid galvanic corrosion. Copper and stainless steel are the most durable metals for flashing.  Galvanized steel, in accordance with ASTM A653, G185 designation, is also suitable for use as flashing. Other Fasteners, Connectors or Hardware as Recommended by the Manufacturer There may be additional products such as polymer or ceramic coatings for fasteners, or vinyl or plastic flashings that are suitable for use with treated wood products.  Consult the individual fastener, connector or flashing manufacturer for recommendations for use of their products with treated wood. Current Recommendations for Drying and Conditioning of Treated Wood Prior to Construction. Wood treated with copper-based preservatives should be at the least surface dried at the treating plant, in the store or at the job site before attachment of fasteners, connectors, flashing or other hardware. A moisture meter with a calibration for preservative treated wood should be used to verify that the wood is within a similar moisture content range to untreated construction lumber (i.e. about 12 to 18%) otherwise the treated wood can undergo similar shrinkage related cracking and deformation as incorrectly conditioned untreated lumber. Canadian Preservation Industry Canada has had a wood preservation industry for more than 100 years.  Canada is tied with the UK as the world’s second largest producer of treated wood (the USA is first, by a large margin).  In 1999, the most recent year for which we have data, Canada produced 3.5 million cubic metres of treated wood.  There are about 60 treating plants in Canada. As with most other industrialized countries, Canada developed a wood preservation industry using creosote, initially to service railroads (the ties holding the rails) and then utilities (power poles).  Creosote production began declining by the 1950s, and by the 1970s was being somewhat replaced for these traditional uses by pentachlorophenol.  Today, these oil-borne preservatives only constitute 17% of Canadian treated wood production. The remaining 83% of production uses water-borne preservatives such as CCA, ACQ, CA and MCA.  The industry began its substantial shift to the water borne

Wood screws are manufactured in many different lengths, diameters and styles. Wood screws in structural framing applications such as fastening floor sheathing to the floors joists or the attachment of gypsum wallboard to wall framing members. Wood screws are often higher in cost than nails due to the machining required to make the thread and the head. Screws are usually specified by gauge number, length, head style, material and finish. Screw lengths between 1 inch and 2 ¾ inch lengths are manufactured in ¼ inch intervals, whereas screws 3 inches and longer, are manufactured in ½ inch intervals. Designers should check with suppliers to determine availability. Design provisions in Canada are limited to 6, 8, 10 and 12 gauge screws and are applicable only for wood screws that meet the requirements of ASME B18.6.1. For wood screw diameters greater than 12 gauge, design should be in accordance with the lag screw requirements of CSA O86. Screws are designed to be much better at resisting withdrawal than nails. The length of the threaded portion of the screw is approximately two-thirds of the screw length. Where the wood relative density is equal to or greater than 0.5, lead holes, at least the length of the threaded portion of the shank, are required. In order to reduce the occurrence of splitting, pre-drilled holes are recommended for all screw connections. The types of wood screws commonly used are shown in Figure 5.4, below. For more information on wood screws, refer to the following resources: ASME B18.6.1 Wood Screws CSA O86 Engineering design in wood

Nailing is the most basic and most commonly used means of attaching members in wood frame construction. Common nails and spiral nails are used extensively in all types of wood construction. Historical performance, along with research results have shown that nails are a viable connection for wood structures with light to moderate loads. They are particularly useful in locations where redundancy and ductile connections are required, such as loading under seismic events. Typical structural applications for nailed connections include: wood frame construction post and beam construction heavy timber construction shearwalls and diaphragms nailed gussets for wood truss construction wood panel assemblies Nails and spikes are manufactured in many lengths, diameters, styles, materials, finishes and coatings, each designed for a specific purpose and application. In Canada, nails are specified by the type and length and are still manufactured to Imperial dimensions. Nails are made in lengths from 13 to 150 mm (1/2 to 6 in). Spikes are made in lengths from 100 to 350 mm (4 to 14 in) and are generally stockier than nails, that is, a spike has a larger cross-sectional area than an equivalent length common nail. Spikes are generally longer and thicker than nails and are generally used to fasten heavy pieces of timber. Nail diameter is specified by gauge number (British Imperial Standard). The gauge is the same as the wire diameter used in the manufacture of the nail. Gauges vary according to nail type and length. In the U.S., the length of nails is designated by “penny” abbreviated “d”. For example, a twenty-penny nail (20d) has a length of four inches. The most common nails are made of low or medium carbon steels or aluminum. Medium-carbon steels are sometimes hardened by heat treating and quenching to increase toughness. Nails of copper, brass, bronze, stainless steel, monel and other special metals are available if specially ordered. Table 1, below, provides examples of some common applications for nails made of different materials. TABLE 1: Nail applications for alternative materials Material Abbreviation Application Aluminum A For improved appearance and long life: increased strain and corrosion resistance. Steel – Mild S For general construction. Steel – Medium Carbon Sc For special driving conditions: improved impact resistance. Stainless steel, copper and silicon bronze E For superior corrosion resistance: more expensive than hot-dip galvanizing. Uncoated steel nails used in areas subject to wetting will corrode, react with extractives in the wood, and result in staining of the wood surface. In addition, the naturally occurring extractives in cedars react with unprotected steel, copper and blued or electro-galvanized fasteners. In such cases, it is best to use nails made of non-corrosive material, such as stainless steel, or finished with non-corrosive material such as hot-dipped galvanized zinc. Table 2, below, provides examples of some common applications for alternative finishes and coatings of nails. TABLE 2: Nail applications for alternative finishes and coatings Nail Finish or Coating Abbreviation Application Bright B For general construction, normal finish, not recommended for exposure to weather. Blued Bl For increased holding power in hardwood, thin oxide finish produced by heat treatment. Heat treated Ht For increased stiffness and holding power: black oxide finish. Phoscoated Pt For increased holding power; not corrosion resistant. Electro galvanized Ge For limited corrosion resistance; thin zinc plating; smooth surface; for interior use. Hot-dip galvanized Ghd For improved corrosion resistance; thick zinc coating; rough surface; for exterior use. Pneumatic or mechanical nailing guns have found wide-spread acceptance in North America due to the speed with which nails can be driven. They are especially cost effective in repetitive applications such as in shearwall construction where nail spacing can be considerably closer together. The nails for pneumatic guns are lightly attached to each other or joined with plastic, allowing quick loading nail clips, similar to joined paper staples. Fasteners for these tools are available in many different sizes and types. Design information provided in CSA O86 is applicable only for common round steel wire nails, spikes and common spiral nails, as defined in CSA B111. The ASTM F1667 Standard is also widely accepted and includes nail diameters that are not included in the CSA B111. Other nail-type fastenings not described in CSA B111 or ASTM F1667 may also be used, if supporting data is available. Types of Nails For more information, refer to the following resources: International, Staple, Nail, and Tool Association (ISANTA) CSA O86 Engineering design in wood CSA B111 Wire Nails, Spikes and Staples ASTM F1667 Standard Specification for Driven Fasteners: Nails, Spikes and Staples

Bolts are widely used in wood construction. They are able to resist moderately heavy loads with relatively few connectors. Bolts may be used in wood-to-wood, wood-to-steel and wood-to-concrete connection types. Some typical structural applications for bolts include: purlin to beam connections beam to column connections column to base connections truss connections timber arches post and beam construction pole-frame construction timber bridges marine structures Several types of bolts as shown in Figure 5.10 below, are used for wood construction with the hexagon head type being the most common. Countersunk heads are used where a flush surface is desired. Carriage bolts can be tightened by turning the nut without holding the bolt since the shoulders under the head grip the wood. Bolts are commonly available in imperial diameters of 1/4, 1/2, 5/8, 3/4, 7/8 and 1 inch. Bolts are installed in holes drilled slightly (1 to 2 mm) larger than the bolt diameter to prevent any splitting and stress development that could be caused by installation or subsequent wood shrinkage. Depending on the diameter, bolts are available in lengths from 75 mm (3″) up to 400 mm (16″) with other lengths available on special order. Bolts can be dipped or plated, at an additional cost, to provide resistance to corrosion. In exposed conditions and high moisture environments, corrosion should be resisted by using hot dip galvanized or stainless steel bolts, washers and nuts. Washers are commonly used with bolts to keep the bolt head or nut from crushing the wood member when tightening is taking place. Washers are not required with a steel side plate, as the bolt head or nut bears directly on the steel. Common types of washers are shown in Figure 5.11 below. Design information provided in CWC’s Wood Design Manual is based on bolts conforming to the requirements of ASTM A307 Standard Specification for Carbon Steel Bolts, Studs, and Threaded Rod 60 000 PSI Tensile Strength or Grade 2 bolts and dowels as specified under SAE J429 Mechanical and Material Requirements for Externally Threaded Fasteners.     Download Figure 5.10 (and 5.11) as a PDF.

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

Many historic structures in North America were built at a time when metal fasteners were not readily available. Instead, wood members were joined by shaping the adjoining wood members to interlock with one another. Timber joinery is a traditional post and beam wood construction technique used to connect wood members without the use of metal fasteners. Timber joinery requires that the ends of timbers are carved out so that they fit together like puzzle pieces. The variations and configurations of wood-to-wood joints is quite large and complex. Some common wood-to-wood timber joints include mortise and tenon, dovetail, tying joint, scarf joint, bevelled shoulder joint, and lap joint. There are many variations and combinations of these and other types of timber joinery. Refer to Figure 5.18, below, for some examples of timber joinery. For load transfer, timber joinery relies upon the interlocking of adjoining wood members. The mated joints are restrained by inserting wooden pegs into holes bored through the interlocked members. A hole about an inch in diameter is drilled right through the joint, and a wooden peg is pounded in to hold the joint together. Metal fasteners require only minimal removal of wood fibre in the area of the fasteners and therefore, the capacity of the system is often governed by the moderate sized wood members to carry horizontal and vertical loads. Timber joinery, on the contrary, requires the removal of a significant volume of wood fibre where joints occur. For this reason, the capacity of traditional timber joinery construction is usually governed by the connections and not by the capacity of the members themselves. To accommodate for the removal of wood fibre at the connection locations, member sizes of wood construction systems that employ timber joinery, such as post and beam construction, are often larger than wood construction systems that make use of metal fasteners. Wood engineering design standards in Canada do not provide specific load transfer information for timber joinery due to their sensitivity to workmanship and material quality. As a result, engineering design must be conservative, often resulting in larger member sizes. The amount of skill and time required for measuring, fitting, cutting, and trial assembly is far greater for timber joinery than for other types of wood construction. Therefore, it is not the most economical means of connecting the members of wood buildings. Timber joinery is not used where economy is the overriding design criteria. Instead, it is used to provide a unique structural appearance which portrays the natural beauty of wood without distraction. Timber joinery offers a unique visual appearance exhibiting a high degree of craftmanship. For further information, refer to the following resources: Timber Framers Guild

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.  

The ICC-ES Listing Report for Self-Tapping Screws for Canada provides third-party evaluation and listing information for self-tapping screws intended for use in Canadian construction applications. The document is intended for designers, engineers, specifiers, and code officials who require verified compliance information to support product approval and specification. The report outlines evaluated products, applicable standards, and conditions of use relevant to Canadian building codes and regulatory requirements. It serves as a reference for understanding the scope of the listing, including performance attributes, installation parameters, and limitations associated with the evaluated self-tapping screw systems. Developed as a compliance and reference document, the ICC-ES Listing Report supports informed decision-making and facilitates code acceptance for self-tapping screws used in wood and hybrid construction in Canada.

This Rothoblaas document explores the critical role that correct installation plays in the performance and reliability of timber screws and structural connections. Aimed at designers, engineers, and construction professionals, the document highlights how improper installation practices can compromise load capacity, durability, and overall structural performance in wood construction. The document examines common causes of connection failure, including incorrect screw selection, installation angle, spacing, and edge distances. It also outlines best practices and practical considerations to help ensure timber screws and connections perform as intended, from design through on-site installation. Developed as an educational resource, this document supports improved understanding of connection behaviour in timber structures, helping project teams reduce risk, improve build quality, and achieve reliable performance through proper installation techniques.