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Construction is the process involved in delivering buildings, infrastructure, industrial facilities, and associated activities through to the end of their life. It typically starts with planning, financing, and design that continues until the asset is built and ready for use. Construction also covers repairs and maintenance work, any work to expand, extend, and improve the asset, and its eventual demolition, dismantling, or decommissioning.

The construction industry contributes significantly to many countries' gross domestic products (GDP). Global expenditure on construction activities was about $4 trillion in 2012. In 2022, expenditure on the construction industry exceeded $11 trillion a year, equivalent to about 13 percent of global GDP. This spending was forecasted to rise to around $14.8 trillion in 2030.^[1]

The construction industry promotes economic development and brings many non-monetary benefits to many countries, but it is one of the most hazardous industries. For example, about 20% (1,061) of US industry fatalities in 2019 happened in construction.^[2]

"Construction" stems from the Latin word constructio (which comes from com- "together" and struere "to pile up") as well as Old French construction.^[3] "To construct" is a verb: the act of building. The noun is "construction": how something is built or the nature of its structure.

The first huts and shelters were constructed by hand or with simple tools. As cities grew during the Bronze Age, a class of professional craftsmen, like bricklayers and carpenters, appeared. Occasionally, slaves were used for construction work. In the Middle Ages, the artisan craftsmen were organized into craft guilds. In the 19th century, steam-powered machinery appeared, and later, diesel- and electric-powered vehicles such as cranes, excavators and bulldozers.

Fast-track construction has been increasingly popular in the 21st century. Some estimates suggest that 40% of construction projects are now fast-track construction.^[4]

Broadly, there are three sectors of construction: buildings, infrastructure and industrial:^[5]

• Building construction is usually further divided into residential and non-residential.
• Infrastructure, also called 'heavy civil' or 'heavy engineering', includes large public works, dams, bridges, highways, railways, water or wastewater and utility distribution.
• Industrial construction includes offshore construction (mainly of energy installations), mining and quarrying, refineries, chemical processing, mills and manufacturing plants.

The industry can also be classified into sectors or markets.^[6] For example, Engineering News-Record (ENR), a US-based construction trade magazine, has compiled and reported data about the size of design and construction contractors. In 2014, it split the data into nine market segments: transportation, petroleum, buildings, power, industrial, water, manufacturing, sewage/waste, telecom, hazardous waste, and a tenth category for other projects.^[7] ENR used data on transportation, sewage, hazardous waste and water to rank firms as heavy contractors.^[8]

The Standard Industrial Classification and the newer North American Industry Classification System classify companies that perform or engage in construction into three subsectors: building construction, heavy and civil engineering construction, and specialty trade contractors. There are also categories for professional services firms (e.g., engineering, architecture, surveying, project management).^[9][10]

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Building construction is the process of adding structures to areas of land, also known as real property sites. Typically, a project is instigated by or with the owner of the property (who may be an individual or an organisation); occasionally, land may be compulsorily purchased from the owner for public use.^[11]

Residential construction may be undertaken by individual land-owners (self-built), by specialist housebuilders, by property developers, by general contractors, or by providers of public or social housing (e.g.: local authorities, housing associations). Where local zoning or planning policies allow, mixed-use developments may comprise both residential and non-residential construction (e.g.: retail, leisure, offices, public buildings, etc.).

Residential construction practices, technologies, and resources must conform to local building authority's regulations and codes of practice. Materials readily available in the area generally dictate the construction materials used (e.g.: brick versus stone versus timber). Costs of construction on a per square meter (or per square foot) basis for houses can vary dramatically based on site conditions, access routes, local regulations, economies of scale (custom-designed homes are often more expensive to build) and the availability of skilled tradespeople.^[12]

Depending upon the type of building, non-residential building construction can be procured by a wide range of private and public organisations, including local authorities, educational and religious bodies, transport undertakings, retailers, hoteliers, property developers, financial institutions and other private companies. Most construction in these sectors is undertaken by general contractors.

Civil engineering covers the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, tunnels, airports, water and sewerage systems, pipelines, and railways.^[13][14] Some general contractors have expertise in civil engineering; civil engineering contractors are firms dedicated to work in this sector, and may specialise in particular types of infrastructure.

Industrial construction includes offshore construction (mainly of energy installations: oil and gas platforms, wind power), mining and quarrying, refineries, food processing plants, breweries and distilleries, power stations, steel mills, warehouses and factories.^[14]

Some construction projects are small renovations or repair jobs, like repainting or fixing leaks, where the owner may act as designer, paymaster and laborer for the entire project. However, more complex or ambitious projects usually require additional multi-disciplinary expertise and manpower, so the owner may commission one or more specialist businesses to undertake detailed planning, design, construction and handover of the work. Often the owner will appoint one business to oversee the project (this may be a designer, a contractor, a construction manager, or other advisors); such specialists are normally appointed for their expertise in project delivery and construction management and will help the owner define the project brief, agree on a budget and schedule, liaise with relevant public authorities, and procure materials and the services of other specialists (the supply chain, comprising subcontractors and materials suppliers). Contracts are agreed for the delivery of services by all businesses, alongside other detailed plans aimed at ensuring legal, timely, on-budget and safe delivery of the specified works.

Design, finance, and legal aspects overlap and interrelate. The design must be not only structurally sound and appropriate for the use and location, but must also be financially possible to build, and legal to use. The financial structure must be adequate to build the design provided and must pay amounts that are legally owed. Legal structures integrate design with other activities and enforce financial and other construction processes.

These processes also affect procurement strategies. Clients may, for example, appoint a business to design the project, after which a competitive process is undertaken to appoint a lead contractor to construct the asset (design–bid–build); they may appoint a business to lead both design and construction (design-build); or they may directly appoint a designer, contractor and specialist subcontractors (construction management).^[15] Some forms of procurement emphasize collaborative relationships (partnering, alliancing) between the client, the contractor, and other stakeholders within a construction project, seeking to ameliorate often highly competitive and adversarial industry practices. DfMA (design for manufacture and assembly) approaches also emphasize early collaboration with manufacturers and suppliers regarding products and components.

Construction or refurbishment work in a "live" environment (where residents or businesses remain living in or operating on the site) requires particular care, planning and communication.^[16]

When applicable, a proposed construction project must comply with local land-use planning policies including zoning and building code requirements. A project will normally be assessed (by the 'authority having jurisdiction', AHJ, typically the municipality where the project will be located) for its potential impacts on neighbouring properties, and upon existing infrastructure (transportation, social infrastructure, and utilities including water supply, sewerage, electricity, telecommunications, etc.). Data may be gathered through site analysis, site surveys and geotechnical investigations. Construction normally cannot start until planning permission has been granted, and may require preparatory work to ensure relevant infrastructure has been upgraded before building work can commence. Preparatory works will also include surveys of existing utility lines to avoid damage-causing outages and other hazardous situations.

Some legal requirements come from malum in se considerations, or the desire to prevent indisputably bad phenomena, e.g. explosions or bridge collapses. Other legal requirements come from malum prohibitum considerations, or factors that are a matter of custom or expectation, such as isolating businesses from a business district or residences from a residential district. An attorney may seek changes or exemptions in the law that governs the land where the building will be built, either by arguing that a rule is inapplicable (the bridge design will not cause a collapse), or that the custom is no longer needed (acceptance of live-work spaces has grown in the community).^[17]

During the construction of a building, a municipal building inspector usually inspects the ongoing work periodically to ensure that construction adheres to the approved plans and the local building code. Once construction is complete, any later changes made to a building or other asset that affect safety, including its use, expansion, structural integrity, and fire protection, usually require municipality approval.

Depending on the type of project, mortgage bankers, accountants, and cost engineers may participate in creating an overall plan for the financial management of a construction project. The presence of the mortgage banker is highly likely, even in relatively small projects since the owner's equity in the property is the most obvious source of funding for a building project. Accountants act to study the expected monetary flow over the life of the project and to monitor the payouts throughout the process. Professionals including cost engineers, estimators and quantity surveyors apply expertise to relate the work and materials involved to a proper valuation.

Financial planning ensures adequate safeguards and contingency plans are in place before the project is started, and ensures that the plan is properly executed over the life of the project. Construction projects can suffer from preventable financial problems.^[18] Underbids happen when builders ask for too little money to complete the project. Cash flow problems exist when the present amount of funding cannot cover the current costs for labour and materials; such problems may arise even when the overall budget is adequate, presenting a temporary issue. Cost overruns with government projects have occurred when the contractor identified change orders or project changes that increased costs, which are not subject to competition from other firms as they have already been eliminated from consideration after the initial bid.^[19] Fraud is also an issue of growing significance within construction.^[20]

Large projects can involve highly complex financial plans and often start with a conceptual cost estimate performed by a building estimator. As portions of a project are completed, they may be sold, supplanting one lender or owner for another, while the logistical requirements of having the right trades and materials available for each stage of the building construction project carry forward. Public–private partnerships (PPPs) or private finance initiatives (PFIs) may also be used to help deliver major projects. According to McKinsey in 2019, the "vast majority of large construction projects go over budget and take 20% longer than expected".^[21]

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A construction project is a complex net of construction contracts and other legal obligations, each of which all parties must carefully consider. A contract is the exchange of a set of obligations between two or more parties, and provides structures to manage issues. For example, construction delays can be costly, so construction contracts set out clear expectations and clear paths to manage delays. Poorly drafted contracts can lead to confusion and costly disputes.

At the start of a project, legal advisors seek to identify ambiguities and other potential sources of trouble in the contract structures, and to present options for preventing problems. During projects, they work to avoid and resolve conflicts that arise. In each case, the lawyer facilitates an exchange of obligations that matches the reality of the project.

Design-bid-build is the most common and well-established method of construction procurement. In this arrangement, the architect, engineer or builder acts for the client as the project coordinator. They design the works, prepare specifications and design deliverables (models, drawings, etc.), administer the contract, tender the works, and manage the works from inception to completion. In parallel, there are direct contractual links between the client and the main contractor, who, in turn, has direct contractual relationships with subcontractors. The arrangement continues until the project is ready for handover.

Design-build became more common from the late 20th century, and involves the client contracting a single entity to provide design and construction. In some cases, the design-build package can also include finding the site, arranging funding and applying for all necessary statutory consents. Typically, the client invites several Design & Build (D&B) contractors to submit proposals to meet the project brief and then selects a preferred supplier. Often this will be a consortium involving a design firm and a contractor (sometimes more than one of each). In the United States, departments of transportation usually use design-build contracts as a way of progressing projects where states lack the skills or resources, particularly for very large projects.^[22]

In a construction management arrangement, the client enters into separate contracts with the designer (architect or engineer), a construction manager, and individual trade contractors. The client takes on the contractual role, while the construction or project manager provides the active role of managing the separate trade contracts, and ensuring that they complete all work smoothly and effectively together. This approach is often used to speed up procurement processes, to allow the client greater flexibility in design variation throughout the contract, to enable the appointment of individual work contractors, to separate contractual responsibility on each individual throughout the contract, and to provide greater client control.

In the industrialized world, construction usually involves the translation of designs into reality. Most commonly (i.e.: in a design-bid-build project), the design team is employed by (i.e. in contract with) the property owner. Depending upon the type of project, a design team may include architects, civil engineers, mechanical engineers, electrical engineers, structural engineers, fire protection engineers, planning consultants, architectural consultants, and archaeological consultants. A 'lead designer' will normally be identified to help coordinate different disciplinary inputs to the overall design. This may be aided by integration of previously separate disciplines (often undertaken by separate firms) into multi-disciplinary firms with experts from all related fields,^[23] or by firms establishing relationships to support design-build processes.

The increasing complexity of construction projects creates the need for design professionals trained in all phases of a project's life-cycle and develop an appreciation of the asset as an advanced technological system requiring close integration of many sub-systems and their individual components, including sustainability. For buildings, building engineering is an emerging discipline that attempts to meet this new challenge.

Traditionally, design has involved the production of sketches, architectural and engineering drawings, and specifications. Until the late 20th century, drawings were largely hand-drafted; adoption of computer-aided design (CAD) technologies then improved design productivity, while the 21st-century introduction of building information modeling (BIM) processes has involved the use of computer-generated models that can be used in their own right or to generate drawings and other visualisations as well as capturing non-geometric data about building components and systems.

On some projects, work on-site will not start until design work is largely complete; on others, some design work may be undertaken concurrently with the early stages of on-site activity (for example, work on a building's foundations may commence while designers are still working on the detailed designs of the building's internal spaces). Some projects may include elements that are designed for off-site construction (see also prefabrication and modular building) and are then delivered to the site ready for erection, installation or assembly.

Once contractors and other relevant professionals have been appointed and designs are sufficiently advanced, work may commence on the project site. Some projects require preliminary works, such as land preparation and levelling, demolition of existing structures (see below), or laying foundations, and there are circumstances where this work may be contracted for in advance of finalising the contract and costs for the whole project.

Typically, a construction site will include a secure perimeter to restrict unauthorised access, site access control points, office and welfare accommodation for personnel from the main contractor and other firms involved in the project team, and storage areas for materials, machinery and equipment. According to the McGraw-Hill Dictionary of Architecture and Construction's definition, construction may be said to have started when the first feature of the permanent structure has been put in place, such as pile driving, or the pouring of slabs or footings.^[24]

Commissioning is the process of verifying that all subsystems of a new building (or other assets) work as intended to achieve the owner's project requirements and as designed by the project's architects and engineers.

A period after handover (or practical completion) during which the owner may identify any shortcomings in relation to the building specification ('defects'), with a view to the contractor correcting the defect.^[25]

Maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, governmental, and residential installations.^[26][27]

Demolition is the discipline of safely and efficiently tearing down buildings and other artificial structures. Demolition contrasts with deconstruction, which involves taking a building apart while carefully preserving valuable elements for reuse purposes (recycling – see also circular economy).

The output of the global construction industry was worth an estimated $10.8 trillion in 2017, and in 2018 was forecast to rise to $12.9 trillion by 2022,^[28] and to around $14.8 trillion in 2030.^[1] As a sector, construction accounts for more than 10% of global GDP (in developed countries, construction comprises 6–9% of GDP),^[29] and employs around 7% of the total employed workforce around the globe^[30] (accounting for over 273 million full- and part-time jobs in 2014).^[31] Since 2010,^[32] China has been the world's largest single construction market.^[33] The United States is the second largest construction market with a 2018 output of $1.581 trillion.^[34]

• In the United States in February 2020, around $1.4 trillion worth of construction work was in progress, according to the Census Bureau, of which just over $1.0 trillion was for the private sector (split roughly 55:45% between residential and nonresidential); the remainder was public sector, predominantly for state and local government.^[35]
• In Armenia, the construction sector experienced growth during the latter part of 2000s. Based on National Statistical Service, Armenia's construction sector generated approximately 20% of Armenia's GDP during the first and second quarters of 2007. In 2009, according to the World Bank, 30% of Armenia's economy was from construction sector.^[36]
• In Vietnam, the construction industry plays an important role in the national economy.^[37][38][39] The Vietnamese construction industry has been one of the fastest growing in the Asia-Pacific region in recent years.^[40][41] The market was valued at nearly $60 billion in 2021.^[42] In the first half of 2022, Vietnam's construction industry growth rate reached 5.59%.^[42][43][44] In 2022, Vietnam's construction industry accounted for more than 6% of the country's GDP, equivalent to over 589.7 billion Vietnamese dong.^[45][46] The industry of industry and construction accounts for 38.26% of Vietnam's GDP.^[47][48][49] At the same time, the industry is one of the most attractive industries for foreign direct investment (FDI) in recent years.^[50][51][52]

Construction is a major source of employment in most countries; high reliance on small businesses, and under-representation of women are common traits. For example:

• In the US, construction employed around 11.4m people in 2020, with a further 1.8m employed in architectural, engineering, and related professional services – equivalent to just over 8% of the total US workforce.^[53] The construction workers were employed in over 843,000 organisations, of which 838,000 were privately held businesses.^[54] In March 2016, 60.4% of construction workers were employed by businesses with fewer than 50 staff.^[55] Women are substantially underrepresented (relative to their share of total employment), comprising 10.3% of the US construction workforce, and 25.9% of professional services workers, in 2019.^[53]
• The United Kingdom construction sector contributed £117 billion (6%) to UK GDP in 2018, and in 2019 employed 2.4m workers (6.6% of all jobs). These worked either for 343,000 'registered' construction businesses, or for 'unregistered' businesses, typically self-employed contractors;^[56] just over one million small/medium-sized businesses, mainly self-employed individuals, worked in the sector in 2019, comprising about 18% of all UK businesses.^[57] Women comprised 12.5% of the UK construction workforce.^[58]

According to McKinsey research, productivity growth per worker in construction has lagged behind many other industries across different countries including in the United States and in European countries. In the United States, construction productivity per worker has declined by half since the 1960s.^[59]

List of countries with the largest construction gross value added in 2018

Economy	Construction GVA in 2018 (billions in USD)
(01)  China	934.2
(02)  United States	839.1
(03)  Japan	275.5
(04)  India	201.2
(05)  Germany	180.5
(06)  United Kingdom	154.7
(07)  France	138.7
(08)  Canada	125.4
(09)  Russia	121.2
(10)  Australia	111.8
(11)  Indonesia	109.7
(12)  South Korea	93.0
(13)  Brazil	92.6
(14)  Mexico	89.0
(15)  Spain	80.0
(16)  Italy	78.9
(17)  Turkey	55.3
(18)  Saudi Arabia	40.2
(19)  Netherlands	39.5
(20)  Poland	39.4
(21)  Switzerland	36.3
(22)  United Arab Emirates	34.5
(23)  Sweden	33.3
(24)  Austria	27.2
(25)  Qatar	27.0
The twenty-five largest countries in the world by construction GVA (2018)[60]

Some workers may be engaged in manual labour^[61] as unskilled or semi-skilled workers; they may be skilled tradespeople; or they may be supervisory or managerial personnel. Under safety legislation in the United Kingdom, for example, construction workers are defined as people "who work for or under the control of a contractor on a construction site";^[62] in Canada, this can include people whose work includes ensuring conformance with building codes and regulations, and those who supervise other workers.^[63]

Laborers comprise a large grouping in most national construction industries. In the United States, for example, in May 2023, the construction sector employed just over 7.9 million people, of whom 859,000 were laborers, while 3.7 million were construction trades workers (including 603,000 carpenters, 559,000 electricians, 385,000 plumbers, and 321,000 equipment operators).^[64] Like most business sectors, there is also substantial white-collar employment in construction - out of 7.9 million US construction sector workers, 681,000 were recorded by the United States Department of Labor in May 2023 as in 'office and administrative support occupations', 620,000 in 'management occupations' and 480,000 in 'business and financial operations occupations'.^[64]

Large-scale construction requires collaboration across multiple disciplines. A project manager normally manages the budget on the job, and a construction manager, design engineer, construction engineer or architect supervises it. Those involved with the design and execution must consider zoning requirements and legal issues, environmental impact of the project, scheduling, budgeting and bidding, construction site safety, availability and transportation of building materials, logistics, and inconvenience to the public, including those caused by construction delays.

Some models and policy-making organisations promote the engagement of local labour in construction projects as a means of tackling social exclusion and addressing skill shortages. In the UK, the Joseph Rowntree Foundation reported in 2000 on 25 projects which had aimed to offer training and employment opportunities for locally based school leavers and unemployed people.^[65] The Foundation published "a good practice resource book" in this regard at the same time.^[66] Use of local labour and local materials were specified for the construction of the Danish Storebaelt bridge, but there were legal issues which were challenged in court and addressed by the European Court of Justice in 1993. The court held that a contract condition requiring use of local labour and local materials was incompatible with EU treaty principles.^[67] Later UK guidance noted that social and employment clauses, where used, must be compatible with relevant EU regulation.^[68] Employment of local labour was identified as one of several social issues which could potentially be incorporated in a sustainable procurement approach, although the interdepartmental Sustainable Procurement Group recognised that "there is far less scope to incorporate [such] social issues in public procurement than is the case with environmental issues".^[69]

There are many routes to the different careers within the construction industry. There are three main tiers of construction workers based on educational background and training, which vary by country:

Unskilled and semi-skilled workers provide general site labor, often have few or no construction qualifications, and may receive basic site training.

Skilled tradespeople have typically served apprenticeships (sometimes in labor unions) or received technical training; this group also includes on-site managers who possess extensive knowledge and experience in their craft or profession. Skilled manual occupations include carpenters, electricians, plumbers, ironworkers, heavy equipment operators and masons, as well as those involved in project management. In the UK these require further education qualifications, often in vocational subject areas, undertaken either directly after completing compulsory education or through "on the job" apprenticeships.^[70]

Professional, technical and managerial personnel often have higher education qualifications, usually graduate degrees, and are trained to design and manage construction processes. These roles require more training as they demand greater technical knowledge, and involve more legal responsibility. Example roles (and qualification routes) include:

• Architect – Will usually have studied architecture to degree level, and then undertaken further study and gained professional experience. In many countries, the title of "architect" is protected by law, strictly limiting its use to qualified people.
• Civil engineer – Typically holds a degree in a related subject and may only be eligible for membership of a professional institution (such as the UK's ICE) following completion of additional training and experience. In some jurisdictions, a new university graduate must hold a master's degree to become chartered,^[a] and persons with bachelor's degrees may become Incorporated Engineers.
• Building services engineer – May also be referred to as an "M&E" or "mechanical, electrical, and plumbing (MEP) engineer" and typically holds a degree in mechanical or electrical engineering.^[a]
• Project manager – Typically holds a 4-year or greater higher education qualification, but are often also qualified in another field such as architecture, civil engineering or quantity surveying.
• Structural engineer – Typically holds a bachelor's or master's degree in structural engineering.^[a]
• Quantity surveyor – Typically holds a bachelor's degree in quantity surveying. UK chartered status is gained from the Royal Institution of Chartered Surveyors.

Construction is one of the most dangerous occupations in the world, incurring more occupational fatalities than any other sector in both the United States and in the European Union.^[2][71] In the US in 2019, 1,061, or about 20%, of worker fatalities in private industry occurred in construction.^[2] In 2017, more than a third of US construction fatalities (366 out of 971 total fatalities) were the result of falls;^[72] in the UK, half of the average 36 fatalities per annum over a five-year period to 2021 were attributed to falls from height.^[73] Proper safety equipment such as harnesses, hard hats and guardrails and procedures such as securing ladders and inspecting scaffolding can curtail the risk of occupational injuries in the construction industry.^[74] Other major causes of fatalities in the construction industry include electrocution, transportation accidents, and trench cave-ins.^[75]

Other safety risks for workers in construction include hearing loss due to high noise exposure, musculoskeletal injury, chemical exposure, and high levels of stress.^[76] Besides that, the high turnover of workers in construction industry imposes a huge challenge of accomplishing the restructuring of work practices in individual workplaces or with individual workers.^[77] Construction has been identified by the National Institute for Occupational Safety and Health (NIOSH) as a priority industry sector in the National Occupational Research Agenda (NORA) to identify and provide intervention strategies regarding occupational health and safety issues.^[78][79] A study conducted in 2022 found “significant effect of air pollution exposure on construction-related injuries and fatalities”, especially with the exposure of nitrogen dioxide.^[80]

Sustainability is an aspect of "green building", defined by the United States Environmental Protection Agency (EPA) as "the practice of creating structures and using processes that are environmentally responsible and resource-efficient throughout a building's life-cycle from siting to design, construction, operation, maintenance, renovation and deconstruction."^[81]

The construction industry may require transformation at pace and at scale if it is to successfully contribute to achieving the target set out in The Paris Agreement of limiting global temperature rise to 1.5C above industrial levels.^[82][83] The World Green Building Council has stated the buildings and infrastructure around the world can reach 40% less embodied carbon emissions but that this can only be achieved through urgent transformation.^[84][85]

Conclusions from industry leaders have suggested that the net zero transformation is likely to be challenging for the construction industry, but it does present an opportunity. Action is demanded from governments, standards bodies, the construction sector, and the engineering profession to meet the decarbonising targets.^[86]

In 2021, the National Engineering Policy Centre published its report Decarbonising Construction: Building a new net zero industry,^[86] which outlined key areas to decarbonise the construction sector and the wider built environment. This report set out around 20 different recommendations to transform and decarbonise the construction sector, including recommendations for engineers, the construction industry and decision makers, plus outlined six-overarching ‘system levers’ where action taken now will result in rapid decarbonisation of the construction sector.^[86] These levels are:

• Setting and stipulating progressive targets for carbon reduction
• Embedding quantitative whole-life carbon assessment into public procurement
• Increasing design efficiency, materials reuse and retrofit of buildings
• Improving whole-life carbon performance
• Improving skills for net zero
• Adopting a joined up, systems approach to decarbonisation across the construction sector and with other sectors

Progress is being made internationally to decarbonise the sector including improvements to sustainable procurement practice such as the CO₂ performance ladder in the Netherlands and the Danish Partnership for Green Public Procurement.^[87][88] There are also now demonstrations of applying the principles of circular economy practices in practice such as Circl, ABN AMRO's sustainable pavilion and the Brighton Waste House.^[89][90][91]

• Engineering News-Record
• Building
• Construction News
• New Civil Engineer
• Concrete and Constructional Engineering
• Consulting-Specifying Engineer
• Construct Ireland
• Building Giants
• List of woodshop magazines

Look up construction in Wiktionary, the free dictionary.

• Agile construction – Management system in the construction industry
• Building material – Material which is used for construction purposes
• Commissioning (construction) – Process to ensure that all building systems perform according to the "Design Intent"
• Environmental impact of concrete
• Impervious surface – Artificial structures such as pavements covered with water-tight materials
• Index of construction articles
• Land degradation – Gradual destruction of land
• List of tallest structures
• List of tallest structures built before the 20th century
• Modern methods of construction – Processes designed to improve upon traditional methods
• Outline of construction – Overview of and topical guide to construction
• Real estate development – Process that creates or renovates new or existing spaces
• Structural robustness – Ability of a structure to withstand physical strain
• Umarell – Bolognese slang term

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Decks lower than fore and aft on a ship

This article is about the traditional use of the term "well deck". For well decks in amphibious warfare ships, see Well dock.

 

In traditional nautical use, well decks were decks lower than decks fore and aft, usually at the main deck level, so that breaks appear in the main deck profile, as opposed to a flush deck profile. The term goes back to the days of sail.^[1] Late-20th-century commercial and military amphibious ships have applied the term to an entirely different type of hangar-like structure, evolving from exaggerated deep "well decks" of World War II amphibious vessels, that can be flooded for lighters or landing craft.

Traditional

[edit]

A well deck is an exposed deck (weather deck) lower than decks fore and aft.^[2] In particular, it is one enclosed by bulwarks limiting flow of water and thus drainage so that design requirements are specific about drainage and maintenance of such drainage with that definition applying even to small vessels. The United States Coast Guard, Sector Upper Mississippi River, Small Passenger Vessel Information Package notes:

'Well deck' means a weather deck fitted with solid bulwarks that impede the drainage of water over the sides or an exposed recess in the weather deck extending 1/2 or more of the length of the vessel over the weather deck.^[3]

Explicit requirements exist for drainage requirements on ships with well decks.^[4] On many vessels the cargo hatches and cargo handling booms and winches were located on the well decks between a central superstructure and raised forecastle and stern.^[5]

Naval vessels into the World War II era often had well decks between stacks with the space sometimes reserved for aircraft and catapults as seen in the photograph of the USS Indianapolis's well deck (note ladders down into the well deck from surrounding decks).

In commercial ship design categories, the "well deck ship" type the profile of the main deck line is broken rather than being flush or unbroken from bow to stern. The earliest cargo steamers were flush deck with openings below rimmed only with low casings. Later designs eliminated this design as dangerous with bulwarks and eventual evolution into the "three island" design^{[Note 1]} with raised forecastle, central bridge and poop superstructures and well decks between.^[6][7]

The well decks of passenger liners were often for the lowest class passengers' use, with the well deck of the Titanic reserved for third class passengers.^[8] By the mid-20th century the concept of well deck design in passenger liners was "old fashioned", and newer ships were designed with flush decks.^[9]

Modern military

[edit]

In modern amphibious warfare usage, a well dock is a hangar-like deck located at the waterline in the stern of some amphibious warfare ships. By taking on water the ship can lower its stern, flooding the well deck and allowing boats, amphibious vehicles and landing craft to dock within the ship. In the United States Navy, this is referred to as a well deck, and officially termed a wet well when the well deck is flooded for operations,^[10]

The structure on the latest naval amphibious ships does not precisely fit the traditional meaning of a weather, or open deck, that is lower than adjacent decks, surrounded by bulkheads and lacking proper drainage would form a catchment for water; however the structure has its origins in such an exaggerated deep deck on World War II era tank landing craft (TLC) the British forces were considering.^[11]

In July 1941 Major R. E. Holloway, Royal Engineers, forwarded a design from a 1924 patent by Otto Popper of the Danube International Commission concerning a barge transporter for Danube barges. The application of that idea to TLCs evolved into the British "Tank Landing Craft carrier" and that would become the Dock Landing Ship (LSD) that had an open, very deep and special purpose well deck open to the elements and thus technically a "well deck" in the traditional definition.^[12]

The structure underwent an evolutionary change to become an enclosed structure, essentially a floodable compartment, for docking amphibious vehicles that in most modern versions has lost its weather deck character even as the more modern commercial ship designs have abandoned the traditional well deck structures that are not typically features of today's bulk cargo ships, container ships or passenger ships.

Some commercial vessels have similar structures for purposes similar to the military versions. The German Baco Liner ships use bow doors. Previous barge carriers were of similar design to the military ships with a large stern well deck.^[13][14] The increased use of containers and container port facilities has decreased the use of this type of commercial vessel with their main use serving regions with less well developed ports.^[15][14]

Wikimedia Commons has media related to Well decks.

• Photo #: NH 104810 USS Suwanee (ID # 1320) "Troops standing in the ship's forward well deck area"
• Wyoming Class (BB-32 and BB-33), 1910 Building Program (showing "A flush-deck hull, raking in an essentially straight line from a high bow to a rather lower stern . . .")
• Manasquan (AG-36) Class: Photographs (showing well deck ship design, search "well deck" in page)

Fibrous material from trees or other plants

 

For a small forest, see Woodland. For wood as a commodity, see Timber. For other uses, see Wood (disambiguation) and Wooden (disambiguation).

 

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Wood samples  Pine   Spruce   Larch   Juniper   Aspen   Hornbeam   Birch   Alder   Beech   Oak   Elm   Cherry   Pear   Maple   Linden   Ash

Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. Being a natural material, it is characterized as an organic material – a natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin and hemicelluloses that resists compression.^[1][2]

Wood is sometimes defined as only the secondary xylem in the stems of trees,^[3] or more broadly to include the same type of tissue elsewhere, such as in the roots of trees or shrubs. In a living tree, it performs a mechanical-support function, enabling woody plants to grow large or to stand up by themselves. It also conveys water and nutrients among the leaves, other growing tissues, and the roots. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, woodchips, or fibers.

Wood has been used for thousands of years for fuel, as a construction material, for making tools and weapons, furniture and paper. More recently it emerged as a feedstock for the production of purified cellulose and its derivatives, such as cellophane and cellulose acetate.

As of 2020, the growing stock of forests worldwide was about 557 billion cubic meters.^[4] As an abundant, carbon-neutral^[5] renewable resource, woody materials have been of intense interest as a source of renewable energy. In 2023, almost 4 billion cubic meters of wood were harvested.^[6] Dominant uses were for furniture and building construction.

Wood is scientifically studied and researched through the discipline of wood science, which was initiated since the beginning of the 20th century.

History

[edit]

A 2011 discovery in the Canadian province of New Brunswick yielded the earliest known plants to have grown wood, approximately 395 to 400 million years ago.^[7][8]

Wood can be dated by carbon dating and in some species by dendrochronology to determine when a wooden object was created.

People have used wood for thousands of years for many purposes, including as a fuel or as a construction material for making houses, tools, weapons, furniture, packaging, artworks, and paper. Known constructions using wood date back ten thousand years. Buildings like the longhouses in Neolithic Europe were made primarily of wood.

Recent use of wood has been enhanced by the addition of steel and bronze into construction.^[9]

The year-to-year variation in tree-ring widths and isotopic abundances gives clues to the prevailing climate at the time a tree was cut.^[10]

Early humans progressively invented tools and techniques for trapping animals. The earliest spears were crafted from wood, with tips toughened by burning. By 15,000 BC, hunters employed wooden and bone spear-launchers to enhance force and distance. These devices were frequently adorned with carvings of creatures.^[11]

Physical properties

[edit]

Growth rings

[edit]

Wood, in the strict sense, is yielded by trees, which increase in diameter by the formation, between the existing wood and the inner bark, of new woody layers which envelop the entire stem, living branches, and roots. This process is known as secondary growth; it is the result of cell division in the vascular cambium, a lateral meristem, and subsequent expansion of the new cells. These cells then go on to form thickened secondary cell walls, composed mainly of cellulose, hemicellulose and lignin.

Where the differences between the seasons are distinct, e.g. New Zealand, growth can occur in a discrete annual or seasonal pattern, leading to growth rings; these can usually be most clearly seen on the end of a log, but are also visible on the other surfaces. If the distinctiveness between seasons is annual (as is the case in equatorial regions, e.g. Singapore), these growth rings are referred to as annual rings. Where there is little seasonal difference growth rings are likely to be indistinct or absent. If the bark of the tree has been removed in a particular area, the rings will likely be deformed as the plant overgrows the scar.

If there are differences within a growth ring, then the part of a growth ring nearest the center of the tree, and formed early in the growing season when growth is rapid, is usually composed of wider elements. It is usually lighter in color than that near the outer portion of the ring, and is known as earlywood or springwood. The outer portion formed later in the season is then known as the latewood or summerwood.^[12] There are major differences, depending on the kind of wood. If a tree grows all its life in the open and the conditions of soil and site remain unchanged, it will make its most rapid growth in youth, and gradually decline. The annual rings of growth are for many years quite wide, but later they become narrower and narrower. Since each succeeding ring is laid down on the outside of the wood previously formed, it follows that unless a tree materially increases its production of wood from year to year, the rings must necessarily become thinner as the trunk gets wider. As a tree reaches maturity its crown becomes more open and the annual wood production is lessened, thereby reducing still more the width of the growth rings. In the case of forest-grown trees so much depends upon the competition of the trees in their struggle for light and nourishment that periods of rapid and slow growth may alternate. Some trees, such as southern oaks, maintain the same width of ring for hundreds of years. On the whole, as a tree gets larger in diameter the width of the growth rings decreases.

As a tree grows, lower branches often die, and their bases may become overgrown and enclosed by subsequent layers of trunk wood, forming a type of imperfection known as a knot. The dead branch may not be attached to the trunk wood except at its base and can drop out after the tree has been sawn into boards. Knots affect the technical properties of the wood, usually reducing tension strength,^[13] but may be exploited for visual effect. In a longitudinally sawn plank, a knot will appear as a roughly circular "solid" (usually darker) piece of wood around which the grain of the rest of the wood "flows" (parts and rejoins). Within a knot, the direction of the wood (grain direction) is up to 90 degrees different from the grain direction of the regular wood.

In the tree a knot is either the base of a side branch or a dormant bud. A knot (when the base of a side branch) is conical in shape (hence the roughly circular cross-section) with the inner tip at the point in stem diameter at which the plant's vascular cambium was located when the branch formed as a bud.

In grading lumber and structural timber, knots are classified according to their form, size, soundness, and the firmness with which they are held in place. This firmness is affected by, among other factors, the length of time for which the branch was dead while the attaching stem continued to grow.

Knots materially affect cracking and warping, ease in working, and cleavability of timber. They are defects which weaken timber and lower its value for structural purposes where strength is an important consideration. The weakening effect is much more serious when timber is subjected to forces perpendicular to the grain and/or tension than when under load along the grain and/or compression. The extent to which knots affect the strength of a beam depends upon their position, size, number, and condition. A knot on the upper side is compressed, while one on the lower side is subjected to tension. If there is a season check in the knot, as is often the case, it will offer little resistance to this tensile stress. Small knots may be located along the neutral plane of a beam and increase the strength by preventing longitudinal shearing. Knots in a board or plank are least injurious when they extend through it at right angles to its broadest surface. Knots which occur near the ends of a beam do not weaken it. Sound knots which occur in the central portion one-fourth the height of the beam from either edge are not serious defects.

Knots do not necessarily influence the stiffness of structural timber; this will depend on the size and location. Stiffness and elastic strength are more dependent upon the sound wood than upon localized defects. The breaking strength is very susceptible to defects. Sound knots do not weaken wood when subject to compression parallel to the grain.

In some decorative applications, wood with knots may be desirable to add visual interest. In applications where wood is painted, such as skirting boards, fascia boards, door frames and furniture, resins present in the timber may continue to 'bleed' through to the surface of a knot for months or even years after manufacture and show as a yellow or brownish stain. A knot primer paint or solution (knotting), correctly applied during preparation, may do much to reduce this problem but it is difficult to control completely, especially when using mass-produced kiln-dried timber stocks.

Heartwood (or duramen^[15]) is wood that as a result of a naturally occurring chemical transformation has become more resistant to decay. Heartwood formation is a genetically programmed process that occurs spontaneously. Some uncertainty exists as to whether the wood dies during heartwood formation, as it can still chemically react to decay organisms, but only once.^[16]

The term heartwood derives solely from its position and not from any vital importance to the tree. This is evidenced by the fact that a tree can thrive with its heart completely decayed. Some species begin to form heartwood very early in life, so having only a thin layer of live sapwood, while in others the change comes slowly. Thin sapwood is characteristic of such species as chestnut, black locust, mulberry, osage-orange, and sassafras, while in maple, ash, hickory, hackberry, beech, and pine, thick sapwood is the rule.^[17] Some others never form heartwood.

Heartwood is often visually distinct from the living sapwood and can be distinguished in a cross-section where the boundary will tend to follow the growth rings. For example, it is sometimes much darker. Other processes such as decay or insect invasion can also discolor wood, even in woody plants that do not form heartwood, which may lead to confusion.

Sapwood (or alburnum^[18]) is the younger, outermost wood; in the growing tree it is living wood,^[19] and its principal functions are to conduct water from the roots to the leaves and to store up and give back according to the season the reserves prepared in the leaves. By the time they become competent to conduct water, all xylem tracheids and vessels have lost their cytoplasm and the cells are therefore functionally dead. All wood in a tree is first formed as sapwood. The more leaves a tree bears and the more vigorous its growth, the larger the volume of sapwood required. Hence trees making rapid growth in the open have thicker sapwood for their size than trees of the same species growing in dense forests. Sometimes trees (of species that do form heartwood) grown in the open may become of considerable size, 30 cm (12 in) or more in diameter, before any heartwood begins to form, for example, in second growth hickory, or open-grown pines.

No definite relation exists between the annual rings of growth and the amount of sapwood. Within the same species the cross-sectional area of the sapwood is very roughly proportional to the size of the crown of the tree. If the rings are narrow, more of them are required than where they are wide. As the tree gets larger, the sapwood must necessarily become thinner or increase materially in volume. Sapwood is relatively thicker in the upper portion of the trunk of a tree than near the base, because the age and the diameter of the upper sections are less.

When a tree is very young it is covered with limbs almost, if not entirely, to the ground, but as it grows older some or all of them will eventually die and are either broken off or fall off. Subsequent growth of wood may completely conceal the stubs which will remain as knots. No matter how smooth and clear a log is on the outside, it is more or less knotty near the middle. Consequently, the sapwood of an old tree, and particularly of a forest-grown tree, will be freer from knots than the inner heartwood. Since in most uses of wood, knots are defects that weaken the timber and interfere with its ease of working and other properties, it follows that a given piece of sapwood, because of its position in the tree, may well be stronger than a piece of heartwood from the same tree.

Different pieces of wood cut from a large tree may differ decidedly, particularly if the tree is big and mature. In some trees, the wood laid on late in the life of a tree is softer, lighter, weaker, and more even textured than that produced earlier, but in other trees, the reverse applies. This may or may not correspond to heartwood and sapwood. In a large log the sapwood, because of the time in the life of the tree when it was grown, may be inferior in hardness, strength, and toughness to equally sound heartwood from the same log. In a smaller tree, the reverse may be true.

In species which show a distinct difference between heartwood and sapwood the natural color of heartwood is usually darker than that of the sapwood, and very frequently the contrast is conspicuous (see section of yew log above). This is produced by deposits in the heartwood of chemical substances, so that a dramatic color variation does not imply a significant difference in the mechanical properties of heartwood and sapwood, although there may be a marked biochemical difference between the two.

Some experiments on very resinous longleaf pine specimens indicate an increase in strength, due to the resin which increases the strength when dry. Such resin-saturated heartwood is called "fat lighter". Structures built of fat lighter are almost impervious to rot and termites, and very flammable. Tree stumps of old longleaf pines are often dug, split into small pieces and sold as kindling for fires. Stumps thus dug may actually remain a century or more since being cut. Spruce impregnated with crude resin and dried is also greatly increased in strength thereby.

Since the latewood of a growth ring is usually darker in color than the earlywood, this fact may be used in visually judging the density, and therefore the hardness and strength of the material. This is particularly the case with coniferous woods. In ring-porous woods the vessels of the early wood often appear on a finished surface as darker than the denser latewood, though on cross sections of heartwood the reverse is commonly true. Otherwise the color of wood is no indication of strength.

Abnormal discoloration of wood often denotes a diseased condition, indicating unsoundness. The black check in western hemlock is the result of insect attacks. The reddish-brown streaks so common in hickory and certain other woods are mostly the result of injury by birds. The discoloration is merely an indication of an injury, and in all probability does not of itself affect the properties of the wood. Certain rot-producing fungi impart to wood characteristic colors which thus become symptomatic of weakness. Ordinary sap-staining is due to fungal growth, but does not necessarily produce a weakening effect.

Water occurs in living wood in three locations, namely:

• in the cell walls
• in the protoplasmic contents of the cells
• as free water in the cell cavities and spaces, especially of the xylem

In heartwood it occurs only in the first and last forms. Wood that is thoroughly air-dried (in equilibrium with the moisture content of the air) retains 8–16% of the water in the cell walls, and none, or practically none, in the other forms. Even oven-dried wood retains a small percentage of moisture, but for all except chemical purposes, may be considered absolutely dry.

The general effect of the water content upon the wood substance is to render it softer and more pliable. A similar effect occurs in the softening action of water on rawhide, paper, or cloth. Within certain limits, the greater the water content, the greater its softening effect. The moisture in wood can be measured by several different moisture meters.

Drying produces a decided increase in the strength of wood, particularly in small specimens. An extreme example is the case of a completely dry spruce block 5 cm in section, which will sustain a permanent load four times as great as a green (undried) block of the same size will.

The greatest strength increase due to drying is in the ultimate crushing strength, and strength at elastic limit in endwise compression; these are followed by the modulus of rupture, and stress at elastic limit in cross-bending, while the modulus of elasticity is least affected.^[14]

Wood is a heterogeneous, hygroscopic, cellular and anisotropic (or more specifically, orthotropic) material. It consists of cells, and the cell walls are composed of micro-fibrils of cellulose (40–50%) and hemicellulose (15–25%) impregnated with lignin (15–30%).^[20]

In coniferous or softwood species the wood cells are mostly of one kind, tracheids, and as a result the material is much more uniform in structure than that of most hardwoods. There are no vessels ("pores") in coniferous wood such as one sees so prominently in oak and ash, for example.

The structure of hardwoods is more complex.^[21] The water conducting capability is mostly taken care of by vessels: in some cases (oak, chestnut, ash) these are quite large and distinct, in others (buckeye, poplar, willow) too small to be seen without a hand lens. In discussing such woods it is customary to divide them into two large classes, ring-porous and diffuse-porous.^[22]

In ring-porous species, such as ash, black locust, catalpa, chestnut, elm, hickory, mulberry, and oak,^[22] the larger vessels or pores (as cross sections of vessels are called) are localized in the part of the growth ring formed in spring, thus forming a region of more or less open and porous tissue. The rest of the ring, produced in summer, is made up of smaller vessels and a much greater proportion of wood fibers. These fibers are the elements which give strength and toughness to wood, while the vessels are a source of weakness.^[23]

In diffuse-porous woods the pores are evenly sized so that the water conducting capability is scattered throughout the growth ring instead of being collected in a band or row. Examples of this kind of wood are alder,^[22] basswood,^[24] birch,^[22] buckeye, maple, willow, and the Populus species such as aspen, cottonwood and poplar.^[22] Some species, such as walnut and cherry, are on the border between the two classes, forming an intermediate group.^[24]

In temperate softwoods, there often is a marked difference between latewood and earlywood. The latewood will be denser than that formed early in the season. When examined under a microscope, the cells of dense latewood are seen to be very thick-walled and with very small cell cavities, while those formed first in the season have thin walls and large cell cavities. The strength is in the walls, not the cavities. Hence the greater the proportion of latewood, the greater the density and strength. In choosing a piece of pine where strength or stiffness is the important consideration, the principal thing to observe is the comparative amounts of earlywood and latewood. The width of ring is not nearly so important as the proportion and nature of the latewood in the ring.

If a heavy piece of pine is compared with a lightweight piece it will be seen at once that the heavier one contains a larger proportion of latewood than the other, and is therefore showing more clearly demarcated growth rings. In white pines there is not much contrast between the different parts of the ring, and as a result the wood is very uniform in texture and is easy to work. In hard pines, on the other hand, the latewood is very dense and is deep-colored, presenting a very decided contrast to the soft, straw-colored earlywood.

It is not only the proportion of latewood, but also its quality, that counts. In specimens that show a very large proportion of latewood it may be noticeably more porous and weigh considerably less than the latewood in pieces that contain less latewood. One can judge comparative density, and therefore to some extent strength, by visual inspection.

No satisfactory explanation can as yet be given for the exact mechanisms determining the formation of earlywood and latewood. Several factors may be involved. In conifers, at least, rate of growth alone does not determine the proportion of the two portions of the ring, for in some cases the wood of slow growth is very hard and heavy, while in others the opposite is true. The quality of the site where the tree grows undoubtedly affects the character of the wood formed, though it is not possible to formulate a rule governing it. In general, where strength or ease of working is essential, woods of moderate to slow growth should be chosen.

In ring-porous woods, each season's growth is always well defined, because the large pores formed early in the season abut on the denser tissue of the year before.

In the case of the ring-porous hardwoods, there seems to exist a pretty definite relation between the rate of growth of timber and its properties. This may be briefly summed up in the general statement that the more rapid the growth or the wider the rings of growth, the heavier, harder, stronger, and stiffer the wood. This, it must be remembered, applies only to ring-porous woods such as oak, ash, hickory, and others of the same group, and is, of course, subject to some exceptions and limitations.

In ring-porous woods of good growth, it is usually the latewood in which the thick-walled, strength-giving fibers are most abundant. As the breadth of ring diminishes, this latewood is reduced so that very slow growth produces comparatively light, porous wood composed of thin-walled vessels and wood parenchyma. In good oak, these large vessels of the earlywood occupy from six to ten percent of the volume of the log, while in inferior material they may make up 25% or more. The latewood of good oak is dark colored and firm, and consists mostly of thick-walled fibers which form one-half or more of the wood. In inferior oak, this latewood is much reduced both in quantity and quality. Such variation is very largely the result of rate of growth.

Wide-ringed wood is often called "second-growth", because the growth of the young timber in open stands after the old trees have been removed is more rapid than in trees in a closed forest, and in the manufacture of articles where strength is an important consideration such "second-growth" hardwood material is preferred. This is particularly the case in the choice of hickory for handles and spokes. Here not only strength, but toughness and resilience are important.^[14]

The results of a series of tests on hickory by the U.S. Forest Service show that:

"The work or shock-resisting ability is greatest in wide-ringed wood that has from 5 to 14 rings per inch (rings 1.8-5 mm thick), is fairly constant from 14 to 38 rings per inch (rings 0.7–1.8 mm thick), and decreases rapidly from 38 to 47 rings per inch (rings 0.5–0.7 mm thick). The strength at maximum load is not so great with the most rapid-growing wood; it is maximum with from 14 to 20 rings per inch (rings 1.3–1.8 mm thick), and again becomes less as the wood becomes more closely ringed. The natural deduction is that wood of first-class mechanical value shows from 5 to 20 rings per inch (rings 1.3–5 mm thick) and that slower growth yields poorer stock. Thus the inspector or buyer of hickory should discriminate against timber that has more than 20 rings per inch (rings less than 1.3 mm thick). Exceptions exist, however, in the case of normal growth upon dry situations, in which the slow-growing material may be strong and tough."^[25]

The effect of rate of growth on the qualities of chestnut wood is summarized by the same authority as follows:

"When the rings are wide, the transition from spring wood to summer wood is gradual, while in the narrow rings the spring wood passes into summer wood abruptly. The width of the spring wood changes but little with the width of the annual ring, so that the narrowing or broadening of the annual ring is always at the expense of the summer wood. The narrow vessels of the summer wood make it richer in wood substance than the spring wood composed of wide vessels. Therefore, rapid-growing specimens with wide rings have more wood substance than slow-growing trees with narrow rings. Since the more the wood substance the greater the weight, and the greater the weight the stronger the wood, chestnuts with wide rings must have stronger wood than chestnuts with narrow rings. This agrees with the accepted view that sprouts (which always have wide rings) yield better and stronger wood than seedling chestnuts, which grow more slowly in diameter."^[25]

In the diffuse-porous woods, the demarcation between rings is not always so clear and in some cases is almost (if not entirely) invisible to the unaided eye. Conversely, when there is a clear demarcation there may not be a noticeable difference in structure within the growth ring.

In diffuse-porous woods, as has been stated, the vessels or pores are even-sized, so that the water conducting capability is scattered throughout the ring instead of collected in the earlywood. The effect of rate of growth is, therefore, not the same as in the ring-porous woods, approaching more nearly the conditions in the conifers. In general, it may be stated that such woods of medium growth afford stronger material than when very rapidly or very slowly grown. In many uses of wood, total strength is not the main consideration. If ease of working is prized, wood should be chosen with regard to its uniformity of texture and straightness of grain, which will in most cases occur when there is little contrast between the latewood of one season's growth and the earlywood of the next.

Structural material that resembles ordinary, "dicot" or conifer timber in its gross handling characteristics is produced by a number of monocot plants, and these also are colloquially called wood. Of these, bamboo, botanically a member of the grass family, has considerable economic importance, larger culms being widely used as a building and construction material and in the manufacture of engineered flooring, panels and veneer. Another major plant group that produces material that often is called wood are the palms. Of much less importance are plants such as Pandanus, Dracaena and Cordyline. With all this material, the structure and composition of the processed raw material is quite different from ordinary wood.

The single most revealing property of wood as an indicator of wood quality is specific gravity (Timell 1986),^[26] as both pulp yield and lumber strength are determined by it. Specific gravity is the ratio of the mass of a substance to the mass of an equal volume of water; density is the ratio of a mass of a quantity of a substance to the volume of that quantity and is expressed in mass per unit substance, e.g., grams per milliliter (g/cm³ or g/ml). The terms are essentially equivalent as long as the metric system is used. Upon drying, wood shrinks and its density increases. Minimum values are associated with green (water-saturated) wood and are referred to as basic specific gravity (Timell 1986).^[26]

The U.S. Forest Products Laboratory lists a variety of ways to define specific gravity (G) and density (ρ) for wood:^[27]

The FPL has adopted G_b and G₁₂ for specific gravity, in accordance with the ASTM D2555^[28] standard. These are scientifically useful, but don't represent any condition that could physically occur. The FPL Wood Handbook also provides formulas for approximately converting any of these measurements to any other.

Wood density is determined by multiple growth and physiological factors compounded into "one fairly easily measured wood characteristic" (Elliott 1970).^[29]

Age, diameter, height, radial (trunk) growth, geographical location, site and growing conditions, silvicultural treatment, and seed source all to some degree influence wood density. Variation is to be expected. The USDA Forest Service measured a coefficient of variation for the specific gravity of wood as 10%^[30]. In other words, about 68% (a standard deviation) of samples will fall within ±10% of the average specific gravity for a given species. Within an individual tree, the variation in wood density is often as great as or even greater than that between different trees (Timell 1986).^[26] Variation of specific gravity within the bole of a tree can occur in either the horizontal or vertical direction.

Because the specific gravity as defined above uses an unrealistic condition, woodworkers tend to use the "average dried weight", which is a density based on mass at 12% moisture content and volume at the same (ρ₁₂). This condition occurs when the wood is at equilibrium moisture content with air at about 65% relative humidity and temperature at 30 °C (86 °F). This density is expressed in units of kg/m³ or lbs/ft³. If you know the specific gravity at 12% MC, G₁₂ (from the Wood Handbook), then multiply by 1120 to get the average dried weight at 12% MC, ρ₁₂, in kg/m³. For example, if G₁₂ is 0.40, then average dried weight is ρ₁₂ = 0.40 * 1120 = 448 kg/m³. You can also find values for dried weight in two other FPL publications, Hardwoods of North America^[31] and Softwoods of North America.^[32]

The following tables list the mechanical properties of wood and lumber plant species, including bamboo. See also Mechanical properties of tonewoods for additional properties.

Wood properties:^[33][34]

Bamboo properties:^[35][34]

It is common to classify wood as either softwood or hardwood. The wood from conifers (e.g. pine) is called softwood, and the wood from dicotyledons (usually broad-leaved trees, e.g. oak) is called hardwood. These names are a bit misleading, as hardwoods are not necessarily hard, and softwoods are not necessarily soft. The well-known balsa (a hardwood) is actually softer than any commercial softwood. Conversely, some softwoods (e.g. yew) are harder than many hardwoods.

There is a strong relationship between the properties of wood and the properties of the particular tree that yielded it, at least for certain species. For example, in loblolly pine, wind exposure and stem position greatly affect the hardness of wood, as well as compression wood content.^[36] The density of wood varies with species. The density of a wood correlates with its strength (mechanical properties). For example, mahogany is a medium-dense hardwood that is excellent for fine furniture crafting, whereas balsa is light, making it useful for model building. One of the densest woods is black ironwood.

The chemical composition of wood varies from species to species, but is approximately 50% carbon, 42% oxygen, 6% hydrogen, 1% nitrogen, and 1% other elements (mainly calcium, potassium, sodium, magnesium, iron, and manganese) by weight.^[37] Wood also contains sulfur, chlorine, silicon, phosphorus, and other elements in small quantity.

Aside from water, wood has three main components. Cellulose, a crystalline polymer derived from glucose, constitutes about 41–43%. Next in abundance is hemicellulose, which is around 20% in deciduous trees but near 30% in conifers. It is mainly five-carbon sugars that are linked in an irregular manner, in contrast to the cellulose. Lignin is the third component at around 27% in coniferous wood vs. 23% in deciduous trees. Lignin confers the hydrophobic properties reflecting the fact that it is based on aromatic rings. These three components are interwoven, and direct covalent linkages exist between the lignin and the hemicellulose. A major focus of the paper industry is the separation of the lignin from the cellulose, from which paper is made.

In chemical terms, the difference between hardwood and softwood is reflected in the composition of the constituent lignin. Hardwood lignin is primarily derived from sinapyl alcohol and coniferyl alcohol. Softwood lignin is mainly derived from coniferyl alcohol.^[38]

Aside from the structural polymers, i.e. cellulose, hemicellulose and lignin (lignocellulose), wood contains a large variety of non-structural constituents, composed of low molecular weight organic compounds, called extractives. These compounds are present in the extracellular space and can be extracted from the wood using different neutral solvents, such as acetone.^[39] Analogous content is present in the so-called exudate produced by trees in response to mechanical damage or after being attacked by insects or fungi.^[40] Unlike the structural constituents, the composition of extractives varies over wide ranges and depends on many factors.^[41] The amount and composition of extractives differs between tree species, various parts of the same tree, and depends on genetic factors and growth conditions, such as climate and geography.^[39] For example, slower growing trees and higher parts of trees have higher content of extractives. Generally, the softwood is richer in extractives than the hardwood. Their concentration increases from the cambium to the pith. Barks and branches also contain extractives. Although extractives represent a small fraction of the wood content, usually less than 10%, they are extraordinarily diverse and thus characterize the chemistry of the wood species.^[42] Most extractives are secondary metabolites and some of them serve as precursors to other chemicals. Wood extractives display different activities, some of them are produced in response to wounds, and some of them participate in natural defense against insects and fungi.^[43]

These compounds contribute to various physical and chemical properties of the wood, such as wood color, fragnance, durability, acoustic properties, hygroscopicity, adhesion, and drying.^[42] Considering these impacts, wood extractives also affect the properties of pulp and paper, and importantly cause many problems in paper industry. Some extractives are surface-active substances and unavoidably affect the surface properties of paper, such as water adsorption, friction and strength.^[39] Lipophilic extractives often give rise to sticky deposits during kraft pulping and may leave spots on paper. Extractives also account for paper smell, which is important when making food contact materials.

Most wood extractives are lipophilic and only a little part is water-soluble.^[40] The lipophilic portion of extractives, which is collectively referred as wood resin, contains fats and fatty acids, sterols and steryl esters, terpenes, terpenoids, resin acids, and waxes.^[44] The heating of resin, i.e. distillation, vaporizes the volatile terpenes and leaves the solid component – rosin. The concentrated liquid of volatile compounds extracted during steam distillation is called essential oil. Distillation of oleoresin obtained from many pines provides rosin and turpentine.^[45]

Most extractives can be categorized into three groups: aliphatic compounds, terpenes and phenolic compounds.^[39] The latter are more water-soluble and usually are absent in the resin.

• Aliphatic compounds include fatty acids, fatty alcohols and their esters with glycerol, fatty alcohols (waxes) and sterols (steryl esters). Hydrocarbons, such as alkanes, are also present in the wood. Suberin is a polyester, made of suberin acids and glycerol, mainly found in barks. Fats serve as a source of energy for the wood cells.^[40] The most common wood sterol is sitosterol, and less commonly sitostanol, citrostadienol, campesterol or cholesterol.^[39]
• The main terpenes occurring in the softwood include mono-, sesqui- and diterpenes.^[40] Meanwhile, the terpene composition of the hardwood is considerably different, consisting of triterpenoids, polyprenols and other higher terpenes. Examples of mono-, di- and sesquiterpenes are α- and β-pinenes, 3-carene, β-myrcene, limonene, thujaplicins, α- and β-phellandrenes, α-muurolene, δ-cadinene, α- and δ-cadinols, α- and β-cedrenes, juniperol, longifolene, cis-abienol, borneol, pinifolic acid, nootkatin, chanootin, phytol, geranyl-linalool, β-epimanool, manoyloxide, pimaral and pimarol. Resin acids are usually tricyclic terpenoids, examples of which are pimaric acid, sandaracopimaric acid, isopimaric acid, abietic acid, levopimaric acid, palustric acid, neoabietic acid and dehydroabietic acid. Bicyclic resin acids are also found, such as lambertianic acid, communic acid, mercusic acid and secodehydroabietic acid. Cycloartenol, betulin and squalene are triterpenoids purified from hardwood. Examples of wood polyterpenes are rubber (cis-polypren), gutta percha (trans-polypren), gutta-balatá (trans-polypren) and betulaprenols (acyclic polyterpenoids).^[39][40] The mono- and sesquiterpenes of the softwood are responsible for the typical smell of pine forest.^[39] Many monoterpenoids, such as β-myrcene, are used in the preparation of flavors and fragrances.^[40] Tropolones, such as hinokitiol and other thujaplicins, are present in decay-resistant trees and display fungicidal and insecticidal properties. Tropolones strongly bind metal ions and can cause digester corrosion in the process kraft pulping. Owing to their metal-binding and ionophoric properties, especially thujaplicins are used in physiology experiments.^[46] Different other in-vitro biological activities of thujaplicins have been studied, such as insecticidal, anti-browning, anti-viral, anti-bacterial, anti-fungal, anti-proliferative and anti-oxidant.^[47][48]
• Phenolic compounds are especially found in the hardwood and the bark.^[40] The most well-known wood phenolic constituents are stilbenes (e.g. pinosylvin), lignans (e.g. pinoresinol, conidendrin, plicatic acid, hydroxymatairesinol), norlignans (e.g. nyasol, puerosides A and B, hydroxysugiresinol, sequirin-C), tannins (e.g. gallic acid, ellagic acid), flavonoids (e.g. chrysin, taxifolin, catechin, genistein). Most of the phenolic compounds have fungicidal properties and protect the wood from fungal decay.^[40] Together with the neolignans the phenolic compounds influence on the color of the wood. Resin acids and phenolic compounds are the main toxic contaminants present in the untreated effluents from pulping.^[39] Polyphenolic compounds are one of the most abundant biomolecules produced by plants, such as flavonoids and tannins. Tannins are used in leather industry and have shown to exhibit different biological activities.^[42] Flavonoids are very diverse, widely distributed in the plant kingdom and have numerous biological activities and roles.^[40]

Global production of roundwood rose from 3.5 billion m³ in 2000 to 4 billion m³ in 2021. In 2021, wood fuel was the main product with a 49 percent share of the total (2 billion m³), followed by coniferous industrial roundwood with 30 percent (1.2 billion m³) and non-coniferous industrial roundwood with 21 percent (0.9 billion m³). Asia and the Americas are the two main producing regions, accounting for 29 and 28 percent of the total roundwood production, respectively; Africa and Europe have similar shares of 20–21 percent, while Oceania produces the remaining 2 percent.^[49]

Wood has a long history of being used as fuel,^[50] which continues to this day, mostly in rural areas of the world. Hardwood is preferred over softwood because it creates less smoke and burns longer. Adding a woodstove or fireplace to a home is often felt to add ambiance and warmth.

Pulpwood is wood that is raised specifically for use in making paper.

Wood has been an important construction material since humans began building shelters, houses and boats. Nearly all boats were made out of wood until the late 19th century, and wood remains in common use today in boat construction. Elm in particular was used for this purpose as it resisted decay as long as it was kept wet (it also served for water pipe before the advent of more modern plumbing).

Wood to be used for construction work is commonly known as lumber in North America. Elsewhere, lumber usually refers to felled trees, and the word for sawn planks ready for use is timber.^[52] In medieval Europe oak was the wood of choice for all wood construction, including beams, walls, doors, and floors. Today a wider variety of woods is used: solid wood doors are often made from poplar, small-knotted pine, and Douglas fir.

New domestic housing in many parts of the world today is commonly made from timber-framed construction. Engineered wood products are becoming a bigger part of the construction industry. They may be used in both residential and commercial buildings as structural and aesthetic materials.

In buildings made of other materials, wood will still be found as a supporting material, especially in roof construction, in interior doors and their frames, and as exterior cladding.

Wood is also commonly used as shuttering material to form the mold into which concrete is poured during reinforced concrete construction.

A solid wood floor is a floor laid with planks or battens created from a single piece of timber, usually a hardwood. Since wood is hydroscopic (it acquires and loses moisture from the ambient conditions around it) this potential instability effectively limits the length and width of the boards.

Solid hardwood flooring is usually cheaper than engineered timbers and damaged areas can be sanded down and refinished repeatedly, the number of times being limited only by the thickness of wood above the tongue.

Solid hardwood floors were originally used for structural purposes, being installed perpendicular to the wooden support beams of a building (the joists or bearers) and solid construction timber is still often used for sports floors as well as most traditional wood blocks, mosaics and parquetry.

Engineered wood products, glued building products "engineered" for application-specific performance requirements, are often used in construction and industrial applications. Glued engineered wood products are manufactured by bonding together wood strands, veneers, lumber or other forms of wood fiber with glue to form a larger, more efficient composite structural unit.^[53]

These products include glued laminated timber (glulam), wood structural panels (including plywood, oriented strand board and composite panels), laminated veneer lumber (LVL) and other structural composite lumber (SCL) products, parallel strand lumber, and I-joists.^[53] Approximately 100 million cubic meters of wood was consumed for this purpose in 1991.^[54] The trends suggest that particle board and fiber board will overtake plywood.

Wood unsuitable for construction in its native form may be broken down mechanically (into fibers or chips) or chemically (into cellulose) and used as a raw material for other building materials, such as engineered wood, as well as chipboard, hardboard, and medium-density fiberboard (MDF). Such wood derivatives are widely used: wood fibers are an important component of most paper, and cellulose is used as a component of some synthetic materials. Wood derivatives can be used for kinds of flooring, for example laminate flooring.

Wood has always been used extensively for furniture, such as chairs and beds. It is also used for tool handles and cutlery, such as chopsticks, toothpicks, and other utensils, like the wooden spoon and pencil.

Further developments include new lignin glue applications, recyclable food packaging, rubber tire replacement applications, anti-bacterial medical agents, and high strength fabrics or composites.^[55] As scientists and engineers further learn and develop new techniques to extract various components from wood, or alternatively to modify wood, for example by adding components to wood, new more advanced products will appear on the marketplace. Moisture content electronic monitoring can also enhance next generation wood protection.^[56]

Wood has long been used as an artistic medium. It has been used to make sculptures and carvings for millennia. Examples include the totem poles carved by North American indigenous people from conifer trunks, often Western Red Cedar (Thuja plicata).

Other uses of wood in the arts include:

• Woodcut printmaking and engraving
• Wood can be a surface to paint on, such as in panel painting
• Many musical instruments are made mostly or entirely of wood

Many types of sports equipment are made of wood, or were constructed of wood in the past. For example, cricket bats are typically made of white willow. The baseball bats which are legal for use in Major League Baseball are frequently made of ash wood or hickory, and in recent years have been constructed from maple even though that wood is somewhat more fragile. National Basketball Association courts have been traditionally made out of parquetry.

Many other types of sports and recreation equipment, such as skis, ice hockey sticks, lacrosse sticks and archery bows, were commonly made of wood in the past, but have since been replaced with more modern materials such as aluminium, titanium or composite materials such as fiberglass and carbon fiber. One noteworthy example of this trend is the family of golf clubs commonly known as the woods, the heads of which were traditionally made of persimmon wood in the early days of the game of golf, but are now generally made of metal or (especially in the case of drivers) carbon-fiber composites.

Little is known about the bacteria that degrade cellulose. Symbiotic bacteria in Xylophaga may play a role in the degradation of sunken wood. Alphaproteobacteria, Flavobacteria, Actinomycetota, Clostridia, and Bacteroidota have been detected in wood submerged for over a year.^[57]

 This article incorporates text from a free content work. Licensed under CC BY-SA IGO 3.0 (license statement/permission). Text taken from World Food and Agriculture – Statistical Yearbook 2023​, FAO.