Engineered wood

thumb|Large self-supporting wooden roof built for [[Expo 2000 in Hanover, Germany]]

Engineered wood, also called mass timber, 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, veneers, or boards of wood, together with adhesives, or other methods of fixation to form composite material. The panels vary in size but can range upwards of and in the case of cross-laminated timber (CLT) can be of any thickness from a few inches to or more. These products are engineered to precise design specifications, which are tested to meet national or international standards and provide uniformity and predictability in their structural performance. 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. The term mass timber describes a group of building materials that can replace concrete assemblies. Such wood-based products typically undergo machine grading in order to be evaluated and categorized for mechanical strength and suitability for specific applications.

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, medium-density fibreboard (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.

thumb|[[Wood–plastic composite, one kind of engineered wood]]

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.

Types of products

thumb|Engineered wood products in a [[Home Depot store]]There are a wide variety of engineered wood products for both structural and non-structural applications. This list is not comprehensive, and is intended to help categorize and distinguish between different types of engineered wood.

Wood-based panels

Wood-based panels are made from fibres, flakes, particles, veneers, chips, sawdust, slabs, wood powder, strands, laminates or other wood derivate through a binding process with adhesives. Wood structural panels are a collection of flat panel products, used extensively in building construction for sheathing, decking, cabinetry and millwork, and furniture. Examples include plywood and oriented strand board (OSB). Non-structural wood-based panels are flat-panel products, used in non-structural construction applications and furniture. Non-structural panels are usually covered with paint, wood veneer, or resin paper in their final form. Examples include fiberboard and particle board.

Plywood

Plywood, a 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 boards and structural composite panels.

Oriented strand board

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 can be cross-oriented to provide strength and stiffness to the panel. Similar to plywood, most OSB panels are delivered with more strength in one direction. The wood strands in the outermost layer on each side of the board are normally aligned into the strongest direction of the board. Arrows on the product will often identify the strongest direction of the board (the height, or longest dimension, in most cases). Produced in huge, continuous mats, OSB is a solid panel product of consistent quality with no laps, gaps, or voids. OSB is delivered in various dimensions, strengths, and levels of water resistance.

OSB and plywood are often used interchangeably in building construction.

Fibreboard

Medium-density fibreboard (MDF) and high-density fibreboard (hardboard or HDF) are made by breaking down hardwood or softwood residuals into wood fibers, combining them with wax and a resin binder, and forming panels by applying high temperature and pressure. MDF is used in non-structural applications.

Particle board

Particle board is manufactured from wood chips, sawmill shavings, or even sawdust, and a synthetic resin or another suitable binder, which is pressed and extruded. Research published in 2017 showed that durable particle board can be produced from agricultural waste products, such as rice husk or guinea corn husk. Particleboard is cheaper, denser, and more uniform than conventional wood and plywood and is substituted for them when the 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. Particle board is used in non-structural applications.

Structural composite lumber

Structural composite lumber (SCL) is a class of materials made with layers of veneers, strands, or flakes bonded with adhesives. Unlike wood structural panels, structural composite lumber products generally have all grain fibers oriented in the same direction. The SCL family of engineered wood products are commonly used in the same structural applications as conventional sawn lumber and timber, including rafters, headers, beams, joists, rim boards, studs, and columns. SCL products have higher dimensional stability and increased strength compared to conventional lumber products.

Laminated veneer

Laminated veneer lumber (LVL) is produced by bonding thin wood veneers together in a large billet, similar to plywood. The grain of all veneers in the LVL billet is parallel to the long direction (unlike plywood). The resulting product features enhanced mechanical properties and dimensional stability that offer a broader range in product width, depth, and length than conventional lumber.

Parallel-strand

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. The length-to-thickness ratio of strands in PSL is about 300. 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. 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 2004, approximately 81% of all wood light framed floors were framed using I-joists.

Mass timber

Mass timber, also known as engineered timber, is a class of large structural wood components for building construction. Mass timber components are made of lumber or veneers bonded with adhesives or mechanical fasteners. Certain types of mass timber, such as nail-laminated timber and glue-laminated timber, have existed for over a hundred years. Mass timber enjoyed increasing popularity from 2012 onward, due to growing concern around the sustainability of building materials, and interest in prefabrication, off site construction, and modularization, for which mass timber is well suited. The various types of mass timber share the advantage of faster construction times as the components are manufactured off-site, and pre-finished to exact dimensions for simple on-site fastening. Mass timber has been shown to have structural properties competitive with steel and concrete, opening the possibility to build large, tall buildings out of wood. Extensive testing has demonstrated the natural fire resistance properties of mass timber primarily due the creation of a char layer around a column or beam which prevents fire from reaching the inner layers of wood.

Cross-laminated timber

Cross-laminated timber (CLT) is a versatile multi-layered panel made of lumber. Each layer of boards is placed perpendicular to adjacent layers for increased rigidity and strength. It is relatively new and gaining popularity within the construction industry as it can be used for long spans and all assemblies, e.g. floors, walls, or roofs.

Glued laminated timber

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.

As the hardwood dowel absorbs moisture from the softwood to reach an equilibrium moisture content, it expands into the surrounding wood, creating a connection and 'locking' them together through friction. The dowels can be dried (such as through a kiln) prior to fitting, to maximize their expansion.

Nail-laminated timber

Nail laminated timber (NLT) is a mass timber product that consists of parallel boards fastened with nails. It can be used to create floors, roofs, walls, and elevator shafts within a building. This increase in density is expected to enhance the strength and stiffness of the wood by a proportional amount. Studies published in 2018 combined chemical processes with traditional mechanical hot press methods. These chemical processes break down lignin and hemicellulose that are found naturally in the wood. Following dissolution, the cellulose strands that remain are mechanically hot compressed. Compared to the three-fold increase in strength observed from hot pressing alone, chemically processed wood has been shown to yield an 11-fold improvement. This extra strength comes from hydrogen bonds formed between the aligned cellulose nanofibers.

The densified wood possessed mechanical strength comparable to steel used in construction, expanding its potential applications beyond those of traditional wood. It also has a lower environmental footprint than steel, requiring significantly less carbon dioxide to produce. A commercial version of densified wood, branded as SuperWood, is being developed by InventWood, a startup based in Maryland. The company plans to begin limited production in 2025, focusing initially on building facade applications.

Synthetic resin densified wood is resin-impregnated densified wood, also known as compreg. Usually phenolic resin is used as impregnation resin to impregnate and laminate plywood layers. Sometimes layers are not impregnated before lamination. It is also possible to impregnate wood chips to produce molded pressed wood components.

Delignified wood

Removing lignin from wood has several other applications, apart from providing structural advantages. Delignification alters the mechanical, thermal, optical, fluidic and ionic properties and functions of the natural wood and is an effective approach to regulating its thermal properties, as it removes the thermally conductive lignin component, while generating a large number of nanopores in the cell walls which help reduce temperature change. Delignified wood reflects most incident light and appears white in color. White wood (also known as nanowood) has high reflection haze, as well as high emissivity in the infrared wavelengths. These two characteristics generate a passive radiative cooling effect, with an average cooling power of over a 24-hour period, Moreover, white wood not only possesses a lower thermal conductivity than natural wood, and it has better thermal performance than most commercially available insulating materials.

White wood can also be put through a compression process, similar to the process mentioned for densified wood, which increases its mechanical performance compared to natural wood (8.7 times higher in tensile strength and 10 times higher in toughness).

Transparent wood composites

Transparent wood composites are new materials, as of 2020 are made at the laboratory scale, that combines transparency and stiffness via a chemical process that replaces light-absorbing compounds, such as lignin, with a transparent polymer.

Environmental benefits

New construction is in high demand due to growing worldwide population. However, the main materials used in new construction are currently steel and concrete. The manufacturing of these materials creates comparatively high emissions of carbon dioxide () into the atmosphere. Engineered wood has the potential to reduce carbon emissions if it replaces steel and/or concrete in the construction of buildings.

In 2014, steel and cement production accounted for about 1320 megatonnes (Mt) and 1740 Mt respectively, which made up about 9% of global emissions that year. In a study that did not take the carbon sequestration potential of engineered wood into account, it was found that roughly 50 Mt e (carbon dioxide equivalent) could be eliminated by 2050 with the full uptake of a hybrid construction system utilizing engineered wood and steel. When considering the added effects that carbon sequestration can have over the lifetime of the material, the emissions reductions of engineered wood is even more substantial, as laminated wood that is not incinerated at the end of its lifecycle absorbs around 582 kg of /m3, while reinforced concrete emits 458 kg /m3 and steel 12.087 kg /m3.

There is not a strong consensus for measuring the carbon sequestration potential of wood. In life-cycle assessment, sequestered carbon is sometimes called biogenic carbon. ISO 21930, a standard that governs life cycle assessment, requires the biogenic carbon from a wood product can only be included as a negative input (i.e. carbon sequestration) when the wood product originated in a sustainably managed forest. This generally means that wood needs to be FSC or SFI-certified to qualify as carbon sequestering.

Advantages

Engineered wood products are used in a variety of ways, often in applications similar to solid wood products:

Mass timber (MT) is lightweight allowing the material to be easily handled, manufactured, and transported. This contributes to it being cost effective and easy to use on site.
MT offers greater strength and stiffness (based on its strength to weight ratio), increased dimensional stability, and uniformity in structures than solid wood.
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.
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.

Disadvantages

Like solid wood, when exposed to high moisture conditions or termites, biodeteriorations and/or fungi decay will occur which reduces the structural integrity and durability of the wood product; essentially the wood will start to rot.
The adhesives used in some products may cause harmful emissions. A concern with some resins is the release of formaldehyde in the finished product, often seen with urea-formaldehyde bonded products.
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.
Polymeric methylene diphenyl diisocyanate () or polyurethane (PU) resins: expensive, generally waterproof, and does not contain formaldehyde, notoriously more difficult to release from platens and engineered wood presses.

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.

Health concerns

While formaldehyde is an essential ingredient of cellular metabolism in mammals, studies have linked prolonged inhalation of formaldehyde gases to cancer. Engineered wood composites have been found to emit potentially harmful amounts of formaldehyde gas in two ways: unreacted free formaldehyde and the chemical decomposition of resin adhesives. When excessive amounts of formaldehyde are added to a process, the surplus will not have any additive to bond with and may seep from the wood product over time. Cheap urea-formaldehyde (UF) adhesives are largely responsible for degraded resin emissions. Moisture degrades the weak UF molecules, resulting in potentially harmful formaldehyde emissions. McLube offers release agents and platen sealers designed for those manufacturers who use reduced-formaldehyde UF and melamine-formaldehyde adhesives. Many OSB and plywood manufacturers use phenol-formaldehyde (PF) because phenol is a much more effective additive. Phenol forms a water-resistant bond with formaldehyde that will not degrade in moist environments. PF resins have not been found to pose significant health risks due to formaldehyde emissions. While PF is an excellent adhesive, the engineered wood industry has started to shift toward polyurethane binders like to achieve even greater water resistance, strength, and process efficiency. are also used extensively in the production of rigid polyurethane foams and insulators for refrigeration. outperform other resin adhesives, but they are notoriously difficult to release and cause buildup on tooling surfaces.

Mechanical fasteners

Some engineered wood products, such as DLT, NLT, and some brands of CLT, can be assembled without the use of adhesives using mechanical fasteners or joinery. These can range from profiled interlocking jointed boards, proprietary metal fixings, nails or timber dowels.

Building codes and standards

Throughout the years mass timber was used in buildings, codes were added to and adopted by the International Building Code (IBC) to create standards for them for the proper use and handling. For example, in 2015, CLT was incorporated into the IBC.

The following technical performance 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 soft boards
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

The following product category rules can be used to create environmental product declarations for engineered wood products:

EN 15804 - Sustainability of construction works - Environmental product declarations - Core rules for the product category of construction products
EN 16485 - Round and sawn timber - Environmental Product Declarations - Product category rules for wood and wood-based products for use in construction (complementary-PCR to EN 15804)
ISO 21930 - Sustainability in buildings and civil engineering works - Core rules for environmental product declarations of construction products and services

Examples of mass timber structures

Plyscrapers

From 1942 to 1943 17 airship hangars in the United States were built of wood, as of war-time shortage no steel was available for their construction.

Plyscrapers are skyscrapers that are either partially made of wood or entirely made of wood. Around the world, many different plyscrapers have been built, including the Ascent MKE building, Mjostarnet in Norway, and the Stadthaus building.

The Ascent MKE building was built in 2022 in Milwaukee, Wisconsin, and is the tallest high-rise building using different mass timber components in combination with some steel and concrete.  This plyscraper is 87 meters tall and has 25 stories.

The Stadthaus building is a residential building built in 2009 in Hackney, London.  It has 9 stories reaching 30 meters tall.  It uses CLT panels as load-bearing walls and floor 'slabs'.

The Black & White Building is an office building topped out in 2023 in Shoreditch, London. It has 6 stories reaching 17.8 meters tall. It uses CLT panels, glulam curtain walling, and LVL columns and beams.

As of 2022, over 84 mass timber buildings at least eight stories tall were in construction or completed worldwide, with numerous other projects in the planning stages. Its environmental benefits and distinctive appearance drive the growing interest in mass timber construction.

Bridges

The Mistissini Bridge built in Quebec, Canada, in 2014 is a 160-meter-long bridge that features both glulam beams and CLT panels.  The bridge was designed to cross over the Uupaachikus Pass.

The Placer River Pedestrian Bridge built in Alaska, United States, in 2013.  It spans long and is located in the Chugach National Forest.  This bridge features glulam as it was used create the trusses.

Notes

References

External links

APA The Engineered Wood Association
Canadian Wood Council Engineered Wood Products