The ABC's of Traditional and Engineered Wood Products

ood frame construction utiliz- accredited by the American Lumber Standards ing traditional and engineered Committee according to the Softwood Lumber Building wood products is the predomi- Standard PS20. nant method of building homes Structural lumber is either visually or mechani- Wand apartments in the United States. Increasingly, cally graded on the basis of its strength; each Blocks wood framing is also being used in commercial grade combination has an assigned design and industrial buildings due to its economy and value. Mechanically graded lumber is typically architectural flexibility. Wood frame buildings used for pre-engineered framing systems such updates and information are economical to build in a wide range of cli- as roof and floor trusses. General classifications on structural materials mate zones. Wood framing is readily available include: dimensional lumber (2x, 3x and 4x) and adaptable to traditional, contemporary and grades and timber grades or classifications known the most futuristic building styles. History has as “Dimension,” “Beams and Stringers,” “Posts demonstrated the inherent strength and durabil- and Timbers,” and “Decking,” with design values ity of wood frame buildings. The purpose of this assigned to each grade. Standard grades for each article is to summarize the various traditional product class should be specified after considering and engineered wood products that are avail- all grades appropriate for the intended use and able throughout North America, and to provide strength requirements. For structural applications, information on how designers can use wood prod- include the required reference design values along ucts to build structures that are both sustainable with the grade that represents those design values. and efficient. It should be noted that, although Also, specify desired moisture content (percent) the authors tried to provide practical informa- such as GREEN or DRY based on requirements tion regarding typical for the product, grade and intended use. structural sizes, design- ers should verify with The ABC’s of Traditional and local suppliers regard- Engineered Wood Products ing availability. Solid Sawn Lumber is a manufactured product derived from a log through sawing and By Michelle Kam-Biron, P.E., S.E., surfacing. Structural and framing lumber is read- SECB and Lori Koch, E.I.T. ily available in rafters, joists and studs from 2x4 Lumber grade stamps. to 2x12 and sometimes 2x14 nominal. Heavy timbers for beams and columns of 4x, 6x, 8x and Glued Laminated Timber (glulam) is made up even up to 20x are available for Western species of wood laminations, or “lams,” that are bonded such as Douglas Fir. With Southern Pine, 2x size together with adhesives. The grain of all lamina- Michelle Kam-Biron, P.E., is typical and can be used to create built up beams tions runs parallel with the length of the member. S.E., SECB, is Director of the of 2 to 3 members for headers, and beams with Individual lams typically are 13/8 inches thick for national education program for 6x6 size for columns. Standard lengths are 8 to Southern Pine and 1½ inches thick for Western the American Wood Council, 20 feet in two-foot increments, although some species, although other thicknesses may also be which provides building industry suppliers may have longer lengths. used. Glulam is available in both stock and custom professionals with continuing Engineered designs that compute the required sizes. Stock beams are manufactured in commonly educational resources on ICC codes sizes of members are based on the standard dressed used dimensions and widths cut to length when and AWC standards. She is also sizes and not the nominal sizes. All solid sawn the beam is ordered from a distributor or dealer. President-Elect of the Structural lumber used for load-bearing purposes, including Typical stock beam widths used in residential Engineers Association of Southern end-jointed structural lumber, are identified by a construction include 31/8, 3½, 51/8, 5½ and 6¾ California. She can be reached at grade mark of a lumber grading/inspection agency inches. For non-residential applications, where [email protected]. Lori Koch, E.I.T., serves as a Project Engineer for the American Wood Council. Lori has presented on various topics ranging from use of general engineering properties of wood, Engineered Wood Products (EWPs), Cross-Laminated Timber (CLT), and green building codes. She can be reached at [email protected].

Glulam beams used in roof system.

Posted with permission by STRUCTURE® magazine  www.STRUCTUREmag.org Unbalanced and balanced glulam layups. Example of glulam with camber. long spans, unusually heavy loads, or other Glulams need to be manufactured and to the long direction. LVLs are available in circumstances control design, custom mem- identified as required in ANSI/AITC A190.1 1¾-inch widths x 5½- to 24-inch depths and bers are typically specified. Common custom Structural Glued Laminated Timber and up to 60-foot lengths. Up to 4 LVLs may be shapes include straight beams, curved beams, ASTM D 3737. Glulam beams will have a connected together to create a larger beam pitched and curved beams, radial arches and trademark that signifies it was manufactured or header. tudor arches. Members can be manufactured in conformance with these provisions. The to any length, but transportation constraints trademark may also include: structural use, must be considered for longer members. mill number, structural grade designation, Glulam may be manufactured as unbalanced and appearance grade. or balanced layups. In unbalanced beams, the Prefabricated Wood I-Joists are “I” shaped quality of lumber used on the tension side of engineered wood structural members that the beam is higher than the lumber used on are prefabricated using sawn or structural Parallel Strand Lumber (PSL) and Laminated the corresponding compression side, allow- composite lumber flanges and OSB or ply- Veneer Lumber (LVL). ing a more efficient use of timber resources. wood webs, bonded together with exterior Balanced members are symmetrical in lumber type adhesives. Typical I-joists for residen- PSL is manufactured from veneer clipped quality about the mid-height of the beam. tial use are available in 9½, 117/8, 14 and into long strands laid in a parallel formation Glulam is available in a range of different 16-inch depths. For I-joists over 22 inches and are typically used as beams, headers and appearances, but having the same structural in depth, the design should consider the pos- columns. PSLs are available in 3½- to 7-inch characteristics for given strength grades. sible requirement of sprinklers in concealed widths x 9¼- to 18-inch depths, and up to Glulam appearance classifications are: spaces. Most manufacturers supply I-joists to 60 foot lengths. Custom depths, achieved Framing, Industrial, Architectural (stock distributors in lengths up to 60 feet. These through secondary lamination, are avail- beams are often supplied with this appear- are frequently cut to lengths of 16 to 36 feet. able up to 54 inches. Similar to LVL, 2 to ance so they may be exposed to view in the Typical applications are as rafters or joists. 3 PSLs can be connected together to create finished structure) and Premium (available Similar to lumber, these framing members a larger beam. only as a custom order where finish appear- can be cut to any length on the jobsite to Single members or assemblies using struc- ance is of primary importance). meet various framing challenges. tural composite lumber (SCL) need to meet Camber is a curvature built into a fabri- Assemblies using prefabricated wood the provisions of ASTM D5456 Standard cated member which opposes the direction I-joists need to meet the provisions of ASTM Specification for Evaluation of Structural and magnitude of the calculated deflection D5055 Standard Specification for Establishing Composite Lumber Products and any addi- that occurs under gravity loads. The glulam and Monitoring Structural Capacities of tional requirements as set forth by governing industry recommends the camber for roof Prefabricated Wood I-Joists, the governing building codes. SCL needs to be identified beams be 1½ times the calculated dead load building code, and any additional require- with the manufacturer’s name and the quality deflection and for floor beams 1.0 times the ments as set forth in the manufacturer’s code assurance agency’s name. calculated dead load. Camber is specified as evaluation report. I-joists need to be identified Wood Structural Panels are wood-based either “inches of camber” or as a radius of with the manufacturer’s name and the quality panel products bonded with a waterproof curvature. Stock beams are typically supplied assurance agency’s name. adhesive. Included under this designation are with a relatively flat camber radius of 3500 Structural Composite Lumber is a family plywood and oriented strand board (OSB). feet or zero camber. of engineered wood products created by layer- Wall and roof sheathing are manufactured ing dried and graded wood veneers or strands in 3/8, 7/16, 15/32, ½, 19/32, 5/8, 23/32, and ¾-inch with moisture resistant adhesive into blocks thicknesses, and floor sheathing is typically of material known as billets, which are subse- 19/32, 5/8, 23/32, ¾, 1, and 11/8-inch thick. quently resawn into specified sizes. Common Plywood is a wood structural panel com- types of SCL include laminated veneer lumber prised of plies of wood veneer arranged in (LVL) and parallel strand lumber (PSL). cross-aligned layers and bonded with an LVL is produced by bonding thin wood adhesive that cures on application of heat Example of glulam grade stamp. veneers, with the grain of the veneers parallel and pressure. Most plywood manufacturers

Posted with permission by STRUCTURE® magazine  www.STRUCTUREmag.org Electronic version posted with permission by STRUCTURE® magazine  October 2014  www.STRUCTUREmag.org produce 4- x 8-foot panels. A few western Table 1. Design references and product standards for various wood products. mills have lathes and presses that can produce Framing Member Design Reference Product Standard panels of 4 x 10, 5 x 10, 4 x 12 and 5 x 12 feet and even fewer that produce 10- and 12-foot Sawn lumber NDS USDOC PS20 panels. Larger panels can be produced by joining two panels together with structural ANSI A190.1 & Structural Glued Laminated Timber NDS scarf or finger joints. ASTM D3737 Oriented strand board (OSB) is a wood structural panel comprised of thin rectangular Prefabricated Wood I-Joists NDS and ER ASTM D5055 wood strands arranged in cross-aligned layers with surface layers, normally arranged in the Structural Composite Lumber NDS and ER ASTM D5456 long panel direction, and bonded with water- proof adhesive. OSB panels are typically 4 x 8 Wood Structural Panels NDS and ER USDOC PS1 & PS2 feet in size. Because OSB is typically manu- factured in large sizes, many manufacturers Cross Laminated Timber ER ANSI/APA PRG 320 can custom-make panels in almost any size by simply altering the cutting pattern. Most solid-sawn lumber or structural compos- safe and sustainable. In 2013, American OSB manufacturers make oversized panels ite lumber where the adjacent layers are Wood Council (AWC) released a series up to 8 x 24 feet, which are typically used cross-oriented and bonded with structural of Environmental Product Declarations for panelized roof systems or modular floors. adhesive to form a solid wood element. (EPDs) for multiple wood products. EPDs Both panels are produced in two bond clas- CLT is a flexible building system suitable are considered a type of environmental sifications – Exterior and Exposure 1. Exterior for use in all assembly types (e.g., walls, label or “ecolabel” – a document that gives panels have bonds capable of withstanding floors and roofs). Panels are prefabricated information regarding the environmental repeated wetting and drying cycles or long- based on the project design requirements characteristics of a product. ISO has devel- term exposure to weather or other conditions and arrive at the job site with windows oped standards on ecolabels that place them of similar severity. Exposure 1 panels are suit- and doors pre-cut. Although size varies by into three broad categories: able for uses not involving long-term exposure manufacturer, they can be as large as 54.1 • Type I – governed by ISO standard to weather. Panels classified as Exposure 1 are x 9.7 x 1.6 feet and include 3, 5, 7, or 14024. Awarded by third party intended to resist the effects of moisture due more layers. Cross-laminated timbers are programs to products demonstrating to construction delays, or other conditions manufactured and identified as required good environmental attributes. of similar severity. in ANSI/APA PRG 320-2011 including • Type II – governed by ISO standard the manufacturer’s name and the quality 14021. Based on self-declared claims assurance agency’s name. by manufacturers about some aspect Table 1 shows which framing member of their product. An example is a types are covered in the National Design manufacturer’s “green” label on their Specification® (NDS®) for Wood Construction biodegradable product. in addition to those covered by national evalu- • Type III – governed by ISO standard ation reports (NER) – also called evaluation 14025. These ecolabels are commonly service reports. Evaluation reports are devel- referred to as EPDs. oped for proprietary products and provide The data reported in a typical EPD is col- designers and code officials with the appro- lected using Life Cycle Assessment (LCA) priate information to design the framing techniques. LCA is a scientific, interna- member per the NDS. tionally-accepted technique for assessing Design values for sawn lumber and glulam potential environmental impacts associ- can be found in the NDS Supplement: Design ated with some or all stages of a product’s Wood structural panel grade stamps. Values for Wood Construction. Design values life. Results of LCA studies are sensitive to for wood I-joists and SCL are provided by system boundaries; different boundaries can The panels need to meet the provisions of the product’s manufacturer. Wood structural give different results for the same product. U.S. Department of Commerce Voluntary panel design data is provided in the NDS, Generic EPDs for the following structural Product Standard 1 (PS1) Structural Plywood, and capacities for shear walls and diaphragms products have been developed: U.S. Department of Commerce Voluntary using WSPs is provided in the Special Design • Softwood Lumber Product Standard 2 (PS2) Performance Provisions for Wind and Seismic (SDPWS). • Softwood Plywood Standard for Wood-Based Structural-Use Design capacities for CLT are provided by • OSB Panels, or applicable code evaluation reports. the manufacturer. • Glulam Each panel will need to be identified for • I-joists grade, bond classification, and Performance Environmental Product •VL L Category by the trademarks of an approved Declarations With the exception of redwood decking, all testing and grading agency. EPDs shown in Table 2 are “cradle-to-gate,” Cross-laminated Timber (CLT) is a As sustainable construction continues to beginning with life-cycle assessment of the prefabricated engineered wood prod- become more mainstream, wood is poised resource, tracking product flows through uct consisting of at least three layers of to help engineers design structures that are the manufacturing process, and ending at

Electronic version posted with permission by STRUCTURE® magazine  October 2014  www.STRUCTUREmag.org the manufacturer’s exit gate, ready for ship- Table 2. Environmental product declarations for structural wood products. ment. It is noted that this limits the ability to account for the benefit of carbon seques- EPD Product Name Date of Issue Scope1 Owner(s)2 tration by offsetting the release of biogenic CO2. This accounting is an accepted prac- Softwood Lumber 16 April 2013 B2B AWC/CWC tice in cradle-to-grave LCA reports, since it is not realized at the point of manufac- turing, but rather occurs over the life cycle Softwood Plywood 16 April 2013 B2B AWC/CWC of the product. These EPDs are compliant with ISO 14025 – Type III Environmental Oriented Strand Board (OSB) 16 April 2013 B2B AWC/CWC Product Declaration, and can be used to earn points in both the LEED and Green Globes Glued Laminated Timbers 16 April 2013 B2B AWC/CWC building certification systems. For more information and to download the free EPDs: www.awc.org/greenbuilding/epd.php.▪ Laminated Veneer Lumber (LVL) 12 July 2013 B2B AWC/CWC

Wood I-Joists 23 July 2013 B2B AWC/CWC

Redwood Decking 17 September 2013 B2C AWC/CRA

1B2B = Business to Business (Cradle-to-Gate); B2C = Business to Consumer (Cradle-to-Grave) 2AWC = American Wood Council; CWC = Canadian Wood Council; CRA = California Redwood Association

The American Wood Council (AWC) is the voice of North American traditional and engi- neered wood products, representing over 75% of the industry. AWC’s engineers, technologists, scientists, and building code experts develop state-of-the-art engineering data, technology, and standards (e.g. NDS) on structural wood products for use by design professionals, build- ing officials, and wood products manufacturers to assure the safe and efficient design and use of wood structural components. www.awc.org [email protected]

Electronic version posted with permission by STRUCTURE® magazine  October 2014  www.STRUCTUREmag.org