2 Engineered wood products, such as oriented strand board and wood I-joists, are commonly used for structural applications.Engineered wood products are a major material in the construction industry, and can be used for most structural applications. Engineered wood panels are commonly used for exterior walls and roof sheathing, and for subfloors in wood-framed floors. Engineered lumber products are frequently used for heavy beams, headers, studs, joists, rafters, and other framing members. See Figure 7-1.
3 Performance rated panels include plywood, oriented strand board, and composite panels. Performance rated panels are manufactured as con-ventional veneered plywood, panels composed of wood strands and fibers such as oriented strand board and hardboard, and structural composite panels composed of veneer faces and reconstituted wood cores. See Figure 7-2.
4 Strength and stiffness properties are affected by wood species. Structural plywood panels are manufactured from softwood lumber. The particular softwood species used for plywood affects the strength and stiffness of ply- wood panels. Most structural plywood is manufactured from Douglas fir and various species of pine. More than 70 other wood species are also used in plywood manufacture. Wood species are classified into five groups, with species in Group 1 being the strongest and Group 5 being the weakest. See Figure 7-3.
5 Cross-lamination provides dimensional stability to plywood panels. Plywood panels consist of an odd number of layers such as three, five, or seven. Each layer consists of one or more plies. A ply is a single veneer sheet. The layers of a plywood panel are cross-laminated, a process in which each layer is placed with its grain at a 90° angle to the adjacent layer. Cross-lamination provides greater strength and stiffness in both directions while minimizing shrinkage and swelling in each direction. The outer layers of the panel are the face veneer and back veneer. The grain direction of the outer layer is always along the longest dimension of a plywood panel. Beneath the outer layers are the crossbands and the core (center layer). See Figure 7-4.
6 The manufacture of plywood begins with peeling veneer strips from peeler logs. The veneer strips are then cross-laminated to produce plywood panels.Continuous strips of veneer are peeled off specially prepared and debarked peeler logs that have been cut from longer logs to a length that will fit into a veneer-cutting lathe. The strips of veneer are cut to length and placed on a revolving table to be sorted by grade. Defects, such as knots and other imperfections in the veneers, are removed using a die cutter. The veneers are then glued and assembled into plywood sheets and subjected to intense heat and pressure in a hot press. See Figure 7-5. The sheets are then trimmed to size and stored in a warehouse for shipment to distributors.
7 Veneers of higher grade are used on the faces and backs of panels that will be exposed. Plywood veneers are graded according to their ap-pearance, natural growth characteristics (such as knots and splits), and the size and number of repairs made during manufacture. High-grade veneers are used as face and back veneers on panels that will be exposed. If both sides of the panel will be exposed, high-grade veneers are used on both sides. If only one side will be exposed, a lower grade veneer is used on the unexposed side. Veneer grades and their descriptions are listed in Figure 7-6.
8 Medium density overlay plywood is used for siding and other exterior applications, and provides a smooth, toothed surface for a paint base.MDO plywood provides a smooth, toothed surface for a paint base, and is recommended for siding and other exterior applications. See Figure 7-7. MDO plywood is also used for built-in furniture and cabinets, and signs. HDO plywood is used for concrete forms, highway signs, countertops, and other demanding applications. HDO plywood concrete forms can be reused 20 to 50 times provided they are properly maintained. HDO plywood is recommended where a smooth concrete finish is desired.
9 Plyform is a performance rated plywood panel that provides a smooth and durable concrete-forming surface.Plyform is a performance rated plywood panel used for concrete forms. Even though other types of exterior plywood panels can be used as concrete forms, Ply- form panels have an overlay which provides additional surface protection. The surface protection, composed of thermosetting resins, increases water, chemical, and abrasion resistance of the forms and increases panel stability, resulting in a smoother, more durable forming surface. See Figure 7-8.
10 Fiberglass-reinforced-plastic plywood panels consist of fiber-reinforced overlays bonded to a plywood panel.Fiberglass-reinforced-plastic (FRP) plywood is an engineered panel product that consists of a tough glass fiber-reinforced overlay bonded to plywood. See Figure 7-9. Overlay materials are as follows:• fiberglass-woven fabric saturated with resin and cured under heat and pressure• glass fiber mats saturated with resin, which are initially cured and bonded to the plywood surface and finally cured in a hot press under heat and pressure• chopped glass strands and resin sprayed on the plywood and cured under heat
11 Oriented strand board is a structural wood panel commonly used for wall sheathing. Oriented strand board (OSB) is structural wood panels manufactured from reconstituted, mechanically oriented wood strands that are bonded with a waterproof adhesive under heat and pressure. OSB is commonly used for roof and wall sheathing, for subfloors, and as the webs of wood I-joists. See Figure OSB is available in 4′ × 8′ and 4′ × 10′ sheets with thicknesses ranging from 1/4″ to 3/4″.
12 The manufacture of oriented strand board (OSB) begins with soaking and debarking logs before they are shredded. Wood strands up to 6″ long are formed into layers and cross-laminated to provide OSB with its strength and dimensional stability.OSB is manufactured from first- and second-growth trees. After logs are shredded into uniform strands up to 6″ long, they are mixed with a waterproof adhesive and a small amount of wax. The strands are then formed into layers with the strands oriented in the same direction. Three to five layers are compressed together, with the strands in each layer at a right angle to the strands of the layer above or below. See Figure The cross-lamination of the strands distributes the wood’s strength in both directions of the panel. Most OSB sheathing panels have a nonskid surface on one side for con-struction site safety.
13 Composite panels have veneer faces with wood fiber crossbands and core. Composite panels are available in three and five layers. Three-layer panels have wood fiber cores and veneer faces and backs. Five-layer panels have a wood fiber core with wood crossbands and veneers on each side. See Figure 7-12.
14 Performance rated panels are identified by trademarks Performance rated panels are identified by trademarks. Additional trademarks and descriptions are shown in the Appendix.A trademark is stamped on one face and one edge of a panel at the time of its manufacture. When different grades of veneer are on the face and back, the trademark is stamped on the side of lesser quality. Examples of typical APA trademarks are shown in Figure 7-13.
15 Hardwood plywood is commonly used for interior finish applications. Hardwood plywood is composed of hardwood face and back veneers with lumber, particleboard, MDF, or hardboard cores joined with an adhesive. The grain of alternate layers is typically at right angles. Hardwood ply-wood is commonly used for interior finish, such as wall paneling and cabinet and door exteriors. See Figure Hardwood plywood is considerably more expensive than construction-grade plywood.
16 Hardwood plywood panel grades are based on natural growth characteristics, including color variations, burls, and pin knots, and the number of repairs in the panel face and back.Hardwood plywood panels are manufactured in ac-cordance with the Hardwood Plywood and Veneer Association (HPVA) standard HP , Hardwood and Decorative Plywood. Hardwood plywood panel grades are based on the number of color streaks or spots, color variations, mineral streaks, burls, pin knots, and small repairs in the panel face and back. See Figure 7-15.
17 Medium density fiberboard is used for a variety of exterior and interior applications including siding. Note the spacer block being used to uniformly space the courses of siding.Medium density fiberboard (MDF) is a nonstructural reconstituted panel product used for a variety of exterior and interior products including siding, molding, furniture, shelving, and cabinets. See Figure MDF is flat, smooth, uniform, dense, and free of knots and grain patterns, allowing MDF to be machined and finished easily. MDF may be sealed with a clear finish, painted, or wrapped with a plastic or paper laminate. Thicknesses range from 1/8″ to 1 1/2″, although other thicknesses are available upon request. Standard panel sizes are 3′ × 8′ and 4′ × 8′.
18 Hardboard is a nonstructural panel product that has no grain pattern and has a uniform density, thickness, and appearance.Hardboard is a nonstructural reconstituted panel product commonly used for paneling, cabinet backs, floor un-derlayment, and exterior siding. See Figure Hard-board does not have a grain pattern and has a uniform density, thickness, and appearance. Hardboard panels are manufactured with one side smooth (S1S) or both sides smooth (S2S). Thicknesses range from 1/12″ to 1 1/8″, with 1/4″, 3/8″ and 5/8″ thicknesses used most often. Hardboard panels are available in 4′ widths, and standard lengths of 8′, 10′, 12′, and 16′.
19 Particleboard is a nonstructural reconstituted panel consisting of particles that are bonded together using a synthetic resin or binder. A plastic laminate is applied to the particleboard for certain applications.Particleboard is a nonstructural reconstituted panel pro-duct consisting of particles of various sizes that are bonded together using a synthetic resin or binder under heat and pressure. Particleboard is commonly used for floor underlayment, shelving, and furniture, and as a core material for composite panels. See Figure Par-ticleboard panels are available in thicknesses ranging from 1/2″ to 1 3/4″, 4′ widths, and standard lengths of 8′, 10′, 12′, and 16′.
20 Glulam timbers are commonly used for beams in commercial and residential construction. Glulam dates back to the early 1900s when the first patents for glulam were obtained in Switzerland and Germany. One of the first glulam structures in the United States was built for the USDA Forest Products Lab-oratory in Since that time, glulam manufacture has evolved, making glulam one of the most widely used engineered lumber products in the construction industry. In the past, glulam was mainly associated with heavy timber construction such as industrial roofing systems, bridges, and marine piers. Glulam timbers are used in residential construction as well as in commercial and industrial construction. See Figure 7-19.
21 Glulam timbers can be formed to produce curves or arches. Glulam timbers are typically manufactured in lengths up to 20′. Longer glulam timbers are produced by finger-jointing the ends of the lams and gluing them together. Continuous straight beams spanning as much as 140′ have been installed on heavy timber projects. Glulams can be curved or arched. See Figure 7-20.
22 Laminated veneer lumber (LVL) is composed of layered veneers and waterproof adhesive and is commonly used for beams. Note the wood I-joists attached to the LVL beam.Laminated veneer lumber (LVL) is an engineered lumber product composed of layered veneers and waterproof adhesive. LVL is commonly used for beams, headers, hip and valley rafters, and flanges for wood I-joists. See Figure LVL is available in thicknesses ranging from 3/4″ to 2 1/2″, with 1 3/4″ thickness commonly used to produce built-up beams. LVL is available in lengths up to 80′, but is most commonly cut into lengths of 48′ and shorter.
23 Parallel strand lumber (PSL) is used for beams, headers, and load-bearing columns. PSL is used for the main beam and supporting column in this application.Parallel strand lumber (PSL) is an engineered lumber product manufactured from strands or elongated flakes of wood that are blended with a waterproof adhesive and cured under pressure. PSL is compatible with common wood-framing materials and is available in standard dimensions. PSL is used for beams and headers, and is frequently used for load-bearing columns. See Figure PSL beams are available in 1 3/4″, 2 11/16″, 3 1/2″, 5 1/4″, and 7″ thicknesses.
24 Wood I-joists are composed of oriented strand board or plywood webs with dimension lumber or laminated veneer lumber flanges.Wood I-joists, or I-beams, are load-bearing structural members consisting of a web placed between top and bottom flanges. Webs are OSB or plywood panels cut to size. Flanges are dimension lumber or LVL. Wood I-joists are used for floor and ceiling joists and rafters in both residential and commercial construction. See Figure 7-23.
25 Rim boards tie together wood I-joists and fill the space between the top plate and bottom plate of two wall sections.OSB rim boards are an engineered wood product used primarily with wood I-joists in floor construction where the ends of the I-joists are fastened to the face of the rim boards. Rim boards fill the space between a sill plate and bottom plate of a wall, or in two-story construction fill the space between the top plate and bottom plate of two wall sections. See Figure In addition, rim boards tie together the floor joists. Rim boards serve the same purpose as header joists in traditional solid lumber construction.
26 The ends of short pieces of lumber are milled to produce fingers The ends of short pieces of lumber are milled to produce fingers. The short pieces are then attached to each other to form finger-jointed lumber, which is used for structural applications such as studs, plates, joists, and rafters.Finger-jointed lumber is an engineered lumber product composed of short pieces of dimension lumber joined end-to-end. The ends of the short pieces are machined with a fingerlike profile and glued together. See Figure Longer lengths of finger-jointed lumber can be produced that have strength equal to conventional dimension lumber. Structural applications of finger-jointed lumber include studs, plates, joists, and rafters.
27 Finger-jointed lumber is divided into two end-use applications Finger-jointed lumber is divided into two end-use applications. Finger-jointed lumber acceptable for all structural applications is stamped with “CERT. EXT. JNTS.” while finger-jointed lumber acceptable only for vertical applications is stamped with “VERTICAL USE ONLY” or “STUD USE ONLY.”Finger-jointed lumber grades are further divided into two end-use applications. Finger-jointed lumber containing “CERT. EXT. JNTS.” in the trademark is acceptable for use in all structural applications, and is manufactured with a waterproof, exterior-type adhesive. Finger-jointed lumber containing “VERTICAL USE ONLY” or “STUD USE ONLY” in the trademark is only used for vertical structural applications such as studs. See Figure 7-26.