Engineered wood, also called composite wood, man-made wood, or manufactured board, includes a range of derivative wood products which are manufactured by binding or fixing the strands, particles, fibres, or veneers or boards of wood, together with adhesives, or other methods of fixation to form composite materials. These products are engineered to precise design specifications which are tested to meet national or international standards. Engineered wood products are used in a variety of applications, from home construction to commercial buildings to industrial products. The products can be used for joists and beams that replace steel in many building projects.
Typically, engineered wood products are made from the same hardwoods and softwoods used to manufacture lumber. Sawmill scraps and other wood waste can be used for engineered wood composed of wood particles or fibers, but whole logs are usually used for veneers, such as plywood, MDF or particle board. Some engineered wood products, like oriented strand board (OSB), can use trees from the poplar family, a common but non-structural species.
Alternatively, it is also possible to manufacture similar engineered bamboo from bamboo; and similar engineered cellulosic products from other lignin-containing materials such as rye straw, wheat straw, rice straw, hemp stalks, kenaf stalks, or sugar cane residue, in which case they contain no actual wood but rather vegetable fibers.
Flat pack furniture is typically made out of man-made wood due to its low manufacturing costs and its low weight, making it easy to transport.
Plywood, wood structural panel, is sometimes called the original engineered wood product. Plywood is manufactured from sheets of cross-laminated veneer and bonded under heat and pressure with durable, moisture-resistant adhesives. By alternating the grain direction of the veneers from layer to layer, or “cross-orienting”, panel strength and stiffness in both directions are maximized. Other structural wood panels include oriented strand board and structural composite panels.
Medium-density fibreboard, is made by breaking down hardwood or softwood residuals into wood fibres, combining it with wax and a resin binder, and forming panels by applying high temperature and pressure.
Particle board is manufactured from wood chips, sawmill shavings, or even sawdust, and a synthetic resin or other suitable binder, which is pressed and extruded. Oriented strand board, also known as flakeboard, waferboard, or chipboard, is similar but uses machined wood flakes offering more strength. Particle board is cheaper, denser and more uniform than conventional wood and plywood and is substituted for them when cost is more important than strength and appearance. A major disadvantage of particleboard is that it is very prone to expansion and discoloration due to moisture, particularly when it is not covered with paint or another sealer.
Oriented strand board (OSB) is a wood structural panel manufactured from rectangular-shaped strands of wood that are oriented lengthwise and then arranged in layers, laid up into mats, and bonded together with moisture-resistant, heat-cured adhesives. The individual layers are cross-oriented to provide strength and stiffness to the panel. Produced in huge, continuous mats, OSB is a solid panel product of consistent quality with no laps, gaps or voids.
Glued laminated timber (glulam) is composed of several layers of dimensional timber glued together with moisture-resistant adhesives, creating a large, strong, structural member that can be used as vertical columns or horizontal beams. Glulam can also be produced in curved shapes, offering extensive design flexibility.
Laminated veneer lumber (LVL) is produced by bonding thin wood veneers together in a large billet. The grain of all veneers in the LVL billet is parallel to the long direction. The resulting product features enhanced mechanical properties and dimensional stability that offer a broader range in product width, depth and length than conventional lumber. LVL is a member of the structural composite lumber (SCL) family of engineered wood products that are commonly used in the same structural applications as conventional sawn lumber and timber, including rafters, headers, beams, joists, rim boards, studs and columns.
Cross-Laminated Timber (CLT) is a versatile multi-layered panel made of lumber. Each layer of boards is placed cross-wise to adjacent layers for increased rigidity and strength. CLT can be used for long spans and all assemblies, e.g. floors, walls or roofs. CLT has the advantage of faster construction times as the panels are manufactured and finished off site and supplied ready to fit and screw together as a flat pack assembly project.
Parallel strand lumber (PSL) consists of long veneer strands laid in parallel formation and bonded together with an adhesive to form the finished structural section. A strong, consistent material, it has a high load carrying ability and is resistant to seasoning stresses so it is well suited for use as beams and columns for post and beam construction, and for beams, headers, and lintels for light framing construction. PSL is a member of the structural composite lumber (SCL) family of engineered wood products.
Laminated strand lumber (LSL) and oriented strand lumber (OSL) are manufactured from flaked wood strands that have a high length-to-thickness ratio. Combined with an adhesive, the strands are oriented and formed into a large mat or billet and pressed. LSL and OSL offer good fastener-holding strength and mechanical connector performance and are commonly used in a variety of applications, such as beams, headers, studs, rim boards, and millwork components. These products are members of the structural composite lumber (SCL) family of engineered wood products. LSL is manufactured from relatively short strands—typically about 1 foot long—compared to the 2 foot to 8 foot long strands used in PSL.
Finger-jointed lumber is made up of short pieces of wood combined to form longer lengths and is used in doorjambs, mouldings and studs. It is also produced in long lengths and wide dimensions for floors.
I-joists and wood I-beams are "I"-shaped structural members designed for use in floor and roof construction. An I-joist consists of top and bottom flanges of various widths united with webs of various depths. The flanges resist common bending stresses, and the web provides shear performance. I-joists are designed to carry heavy loads over long distances while using less lumber than a dimensional solid wood joist of a size necessary to do the same task . As of 2005, approximately half of all wood light framed floors were framed using I-joists .
Roof trusses and floor trusses are structural frames relying on a triangular arrangement of webs and chords to transfer loads to reaction points. For a given load, long wood trusses built from smaller pieces of lumber require less raw material and make it easier for AC contractors, plumbers, and electricians to do their work, compared to the long 2x10s and 2x12s traditionally used as rafters and floor joists.
Transparent wood composites are new composites made at the laboratory scale that combine transparency and stiffness. They are not available yet on the market.
Engineered wood products are used in a variety of ways, often in applications similar to solid wood products. Engineered wood products may be preferred over solid wood in some applications due to certain comparative advantages:Engineered wood is felt to offer structural advantages for home construction.
Because engineered wood is man-made, it can be designed to meet application-specific performance requirements.
Engineered wood products are versatile and available in a wide variety of thicknesses, sizes, grades, and exposure durability classifications, making the products ideal for use in unlimited construction, industrial and home project application.
Engineered wood products are designed and manufactured to maximize the natural strength and stiffness characteristics of wood. The products are very stable and some offer greater structural strength than typical wood building materials.
Glued laminated timber (glulam) has greater strength and stiffness than comparable dimensional lumber and, pound for pound, is stronger than steel.
Some engineered wood products offer more design options without sacrificing structural requirements.
Engineered wood panels are easy to work with using ordinary tools and basic skills. They can be cut, drilled, routed, jointed, glued, and fastened. Plywood can be bent to form curved surfaces without loss of strength. And large panel size speeds construction by reducing the number of pieces to be handled and installed.
Engineered wood products make more efficient use of wood. They can be made from small pieces of wood, wood that has defects or underutilized species.
Wooden trusses are competitive in many roof and floor applications, and their high strength-to-weight ratios permit long spans offering flexibility in floor layouts.
Sustainable design advocates recommend using engineered wood, which can be produced from relatively small trees, rather than large pieces of solid dimensional lumber, which requires cutting a large tree.
Some products may burn more quickly than solid lumber.
They require more primary energy for their manufacture than solid lumber.
The adhesives used in some products may be toxic. A concern with some resins is the release of formaldehyde in the finished product, often seen with urea-formaldehyde bonded products.
Cutting and otherwise working with some products can expose workers to toxic compounds.
Some engineered wood products, such as those specified for interior use, may be weaker and more prone to humidity-induced warping than equivalent solid woods. Most particle and fiber-based boards are not appropriate for outdoor use because they readily soak up water.
Plywood and OSB typically have a density of 35 to 40 pounds per cubic foot (550 to 650 kg per cubic meter). For example, 3/8" plywood sheathing or OSB sheathing typically has a weight of 1.0 to 1.2 pounds per square foot.
The lamella is the face layer of the wood that is visible when installed. Typically, it is a sawn piece of timber. The timber can be cut in three different styles: flat-sawn, quarter-sawn, and rift-sawn. Keep in mind that each cut will give the board a different final appearance.
- Wood ply construction ("sandwich core"): Uses multiple thin plies of wood adhered together. The wood grain of each ply runs perpendicular to the ply below it. Stability is attained from using thin layers of wood that have little to no reaction to climatic change. The wood is further stabilized due to equal pressure being exerted lengthwise and widthwise from the plies running perpendicular to each other.
- Finger core construction: Finger core engineered wood floors are made of small pieces of milled timber that run perpendicular to the top layer (lamella) of wood. They can be 2-ply or 3-ply, depending on their intended use. If it is three ply, the third ply is often plywood that runs parallel to the lamella. Stability is gained through the grains running perpendicular to each other, and the expansion and contraction of wood is reduced and relegated to the middle ply, stopping the floor from gapping or cupping.
- Fibreboard: The core is made up of medium or high density fibreboard. Floors with a fibreboard core are hygroscpoic and must never be exposed to large amounts of water or very high humidity - the expansion caused from absorbing water combined with the density of the fibreboard, will cause it to lose its form. Fibreboard is less expensive than timber and can emit higher levels of harmful gases due to its relatively high adhesive content.
- An engineered flooring construction which is popular in parts of Europe is the hardwood lamella, softwood core laid perpendicular to the lamella, and a final backing layer of the same noble wood used for the lamella. Other noble hardwoods are sometimes used for the back layer but must be compatible. This is thought by many to be the most stable of engineered floors.
Engineered wood flooring is mainly industrially fabricated in the form of straight edged boards, with milled jointing profiles to provide for interconnecting of the boards. Such manufacturing is most cost efficient but leaves an industrial looking surface. In nature no straight lines exist; therefore there is a rising trend to modify the visual appearance to imitate it. In recent years numerous producers have been taking on the challenge of adding more natural aesthetics.
The types of adhesives used in engineered wood include:Urea-formaldehyde resins (UF)
most common, cheapest, and not waterproof.
Phenol formaldehyde resins (PF)
yellow/brown, and commonly used for exterior exposure products.
Melamine-formaldehyde resins (MF)
white, heat and water resistant, and often used in exposed surfaces in more costly designs.
Methylene diphenyl diisocyanate (MDI) or polyurethane (PU) resins
expensive, generally waterproof, and does not contain formaldehyde.
A more inclusive term is structural composites. For example, fiber cement siding is made of cement and wood fiber, while cement board is a low density cement panel, often with added resin, faced with fiberglass mesh.
Some engineered products such as CLT Cross Laminated Timber can be assembled without the use of adhesives using mechanical fixing. These can range from profiled interlocking jointed boards, proprietary metal fixings, nails or timber dowels (Brettstapel - single layer or CLT).
The following standards are related to engineered wood products:EN 300 - Oriented Strand Boards (OSB) — Definitions, classification and specifications
EN 309 - Particleboards — Definition and classification
EN 338 - Structural timber - Strength classes
EN 386 - Glued laminated timber — performance requirements and minimum production requirements
EN 313-1 - Plywood — Classification and terminology Part 1: Classification
EN 313-2 - Plywood — Classification and terminology Part 2: Terminology
EN 314-1 - Plywood — Bonding quality — Part 1: Test methods
EN 314-2 - Plywood — Bonding quality — Part 2: Requirements
EN 315 - Plywood — Tolerances for dimensions
EN 387 - Glued laminated timber — large finger joints - performance requirements and minimum production requirements
EN 390 - Glued laminated timber — sizes - permissible deviations
EN 391 - Glued laminated timber — shear test of glue lines
EN 392 - Glued laminated timber — Shear test of glue lines
EN 408 - Timber structures — Structural timber and glued laminated timber — Determination of some physical and mechanical properties
EN 622-1 - Fibreboards — Specifications — Part 1: General requirements
EN 622-2 - Fibreboards — Specifications — Part 2: Requirements for hardboards
EN 622-3 - Fibreboards — Specifications — Part 3: Requirements for medium boards
EN 622-4 - Fibreboards — Specifications — Part 4: Requirements for softboards
EN 622-5 - Fibreboards — Specifications — Part 5: Requirements for dry process boards (MDF)
EN 1193 - Timber structures — Structural timber and glued laminated timber - Determination of shear strength and mechanical properties perpendicular to the grain
EN 1194 - Timber structures — Glued laminated timber - Strength classes and determination of characteristic values
EN 1995-1-1 - Eurocode 5: Design of timber structures — Part 1-1: General — Common rules and rules for buildings
EN 12369-1 - Wood-based panels — Characteristic values for structural design — Part 1: OSB, particleboards and fibreboards
EN 12369-2 - Wood-based panels — Characteristic values for structural design — Part 2: Plywood
EN 12369-3 - Wood-based panels — Characteristic values for structural design — Part 3: Solid wood panels
EN 14080 - Timber structures — Glued laminated timber — Requirements
EN 14081-1 - Timber structures - Strength graded structural timber with rectangular cross section - Part 1: General requirements