BUILDING CONSTRUCTION

the techniques and industry involved in the assembly and erection of structures, primarily those used to provide shelter. Building construction is an ancient human activity. It began with the purely functional need for a controlled environment to moderate the effects of climate. Constructed shelters were one means by which human beings were able to adapt themselves to a wide variety of climates and become a global species. Human shelters were at first very simple and perhaps lasted only a few days or months. Over time, however, even temporary structures evolved into such highly refined forms as the igloo. Gradually more durable structures began to appear, particularly after the advent of agriculture, when people began to stay in one place for long periods. The first shelters were dwellings, but later other functions, such as food storage and ceremony, were housed in separate buildings. Some structures began to have symbolic as well as functional value, marking the beginning of the distinction between architecture and building. The history of building is marked by a number of trends. One is the increasing durability of the materials used. Early building materials were perishable, such as leaves, branches, and animal hides. Later, more durable natural materialssuch as clay, stone, and timberand, finally, synthetic materialssuch as brick, concrete, metals, and plasticswere used. Another is a quest for buildings of ever greater height and span; this was made possible by the development of stronger materials and by knowledge of how materials behave and how to exploit them to greater advantage. A third major trend involves the degree of control exercised over the interior environment of buildings: increasingly precise regulation of air temperature, light and sound levels, humidity, odours, air speed, and other factors that affect human comfort has been possible. Yet another trend is the change in energy available to the construction process, starting with human muscle power and developing toward the powerful machinery used today. The present state of building construction is complex. There is a wide range of building products and systems which are aimed primarily at groups of building types or markets. The design process for buildings is highly organized and draws upon research establishments that study material properties and performance, code officials who adopt and enforce safety standards, and design professionals who determine user needs and design a building to meet those needs. The construction process is also highly organized; it includes the manufacturers of building products and systems, the craftsmen who assemble them on the building site, the contractors who employ and coordinate the work of the craftsmen, and consultants who specialize in such aspects as construction management, quality control, and insurance. Building construction today is a significant part of industrial culture, a manifestation of its diversity and complexity and a measure of its mastery of natural forces, which can produce a widely varied built environment to serve the diverse needs of society. This article first traces the history of building construction, then surveys its development at the present time. For treatment of the aesthetic considerations of building design, see architecture. For further treatment of historical development, see African arts; architecture, history of; Central Asian arts; East Asian arts; Egyptian arts; Islamic arts; South Asian arts; and Southeast Asian arts. the techniques and industry involved in the assembly and erection of structures, primarily those used to provide shelter. Early man built with reeds, grasses and trees, animal skins, stones, ice, and mud. As construction evolved, however, two basic materials came to the fore: wood and stone. In Europe and other places where timber was available, wood was split into planks and then cut into posts that could be used to support a roof and to subdivide the space into multiple units, or rooms. Stone construction can be traced to the 3rd and 4th millennium BC, when the Egyptians began building their palaces, temples, and tombs out of limestone. The precision and durability of their work is evident in such extant structures as the pyramids. The ancient Greeks built with pieces of stone that were skillfully fitted together and sometimes bonded with clay. They subsequently developed mortar, and by the 2nd century BC this was being mixed with stone to make concrete. Made from clays, and easier to use than stone because of their size and standardization, bricks made possible the construction of the arches, vaults, and domes that were popular in Europe from the Roman era on. With the Industrial Revolution of the 18th century, iron brought on a new era in building in which rigid frames could be riveted together to support a building's weight. Iron was quickly replaced by steel in the early 20th century, and this development, along with the invention of modern concrete in the 1870s, made possible the multistoried buildings that epitomize modern building construction. At the end of World War II, shortage of labour, extensive demand for housing because of bombings, and government participation led to the widespread development of prefabricated building systems. The design, manufacture, transportation, and erection of components could be accomplished for many structures from a single source company, utilizing interchangeable parts. Before most buildings are constructed, the function of the proposed building must be determined, a geographic location chosen, a cost estimate drawn up, and a design plan accompanied by sketches prepared by an architect. Architectural design proceeds in a series of stages of increasing detail and specificity. Schematic design sketches that give a rough idea of the building's look and form are followed by detailed development design, comprising drawings of plans, elevations, building cross sections, and perspectives. These are followed by working drawings and specifications, which are contract documents that describe the design, location, and dimensions of the elements of the building and that also describe the quality of materials and workmanship to be used in the construction of the building. Surveying and laying out, or locating, the foundation are the first steps in the actual construction of most buildings. The foundation itself (those portions of a building resting upon earth or rock) is dependent on the weight of the building and on the resistance of the earth on which it rests. These two factors must balance each other for the foundation to be cohesive and for excessive or unequal settling of the building to be avoided. Small buildings such as residences usually use a masonry wall foundation, consisting of a horizontal slab of concrete with a continuous vertical ledge of concrete on its outer rim, upon which the walls of the building are supported. Larger, heavier buildings have supporting steel columns embedded in the concrete foundation, and the foundation itself may be augmented by steel or concrete piles driven deep into the soil to provide extra stability. The three major types of structural frames are wood, steel, and concrete. Wood frames are light, cheap, and simple, consisting of interlocking arrays of vertical and horizontal beams and studs. Steel structural frames consist of vertical members (columns) and horizontal members (girders and beams) that are riveted, bolted, or welded together. Concrete structural frames have the advantage of costing less than steel ones, but they must usually be reinforced by steel to carry heavy loads. Steel rods are positioned in an interconnected framework surrounded by a wooden or steel form, and then concrete is poured into the form. The form is withdrawn once the concrete has set. In a method known as prestressing, high-strength wires are stretched and held tight while concrete is set around them. In this way a concrete span as long as 100 feet (30 m) can be attained. Flooring must support whatever loads are to be placed within the structure, and it must transmit its load to the structural frame. Roofing may be flat or pitched, depending upon the type of framing, the load to be carried, fire resistance required, and the overall character of the building. Structural elements called trusses, which are composed of interfaced triangles, can be utilized to make vast roof spans possible. There are a number of auxiliaries necessary in a building, including insulation, usually accomplished by filling in spaces within flooring or walls with fire-resistant material; ventilation, provided by complex systems of ducts or by windows; electricity, which is wired beneath or within the finished walls; plumbing (both for provision of clean water and for the disposal of wastes), using cast-iron pipe inside and clay pipe underground outside; and heating and air-conditioning, which may be accomplished by a steam boiler system, electricity, gas, or other energy source, such as solar radiation. Additional reading General Hugh Brooks, Encyclopedia of Building and Construction Terms (1983), provides useful reference information in nontechnical language; Henry J. Cowan (ed.), Encyclopedia of Building Technology (1988), is a collection of informative articles by authoritative contributors from 15 countries; and Joseph A. Wilkes and Robert T. Packard (eds.), Encyclopedia of Architecture: Design, Engineering & Construction, 5 vol. (198889), offers an extensive coverage of a broad spectrum of topics. See also Cyril M. Harris (ed.), Dictionary of Architecture and Construction (1975); and Kornelis Smit (ed.), Means Illustrated Construction Dictionary (1985). History Banister Fletcher, Sir Banister Fletcher's A History of Architecture, 19th ed., edited by John Musgrove (1987), is the most comprehensive exploration of comparative methods. The early history of building materials and building techniques is covered in Norman Davey, A History of Building Materials (1961, reissued 1971); Ren Alleau, History of the Great Building Constructions (1967; originally published in French, 1966); Henry J. Cowan, The Master Builders: A History of Structural and Environmental Design from Ancient Egypt to the Nineteenth Century (1977, reprinted 1985); and John Fitchen, Building Construction Before Mechanization (1986). Specific urban cultures are the basis of the analyses in Jean Gimpel, The Cathedral Builders, trans. by Teresa Waugh (1983; originally published in French, 1958); John Fitchen, The Construction of Gothic Cathedrals: A Study of Medieval Vault Erection (1961, reissued 1981); Frank D. Prager and Gustina Scaglia, Brunelleschi: Studies of His Technology and Inventions (1970); and E. Baldwin Smith, The Dome: A Study in the History of Ideas (1950; reissued 1978). For the industrial age, see Carl W. Condit, American Building Art: The Nineteenth Century (1960), American Building Art: The Twentieth Century (1961), American Building: Materials and Techniques from the First Colonial Settlements to the Present, 2nd ed. (1982), and The Rise of the Skyscraper (1952); Sigfried Giedion, Mechanization Takes Command: A Contribution to Anonymous History (1948, reprinted 1969), and Space, Time, and Architecture: The Growth of a New Tradition, 5th rev. ed. (1967); Reyner Banham, The Architecture of the Well-Tempered Environment, 2nd ed. (1984); and Henry J. Cowan, Science and Building: Architectural and Environmental Design in the Nineteenth and Twentieth Centuries (1978). Modern practices Standards regulating building construction are covered in Building Officials And Code Administrators International, The BOCA Basic/National Building Code (triennial); International Conference Of Building Officials, Uniform Building Code (triennial); Southern Building Code Congress, Southern Standard Building Code (irregular); and American Society Of Heating, Refrigerating, And Air-conditioning Engineers, ASHRAE Guide and Data Book (annual). See also Frederick S. Merritt (ed.), Building Design and Construction Handbook, 4th ed. (1982); and Charles A. Herubin, Construction Site Planning and Development (1988). Standards and data pertaining to architecture, building, and allied fields are illustrated in John Ray Hoke, Jr. (ed.), Ramsey/Sleeper Architectural Graphic Standards, 8th ed. (1988). See also Albert G.H. Dietz, Dwelling House Construction, 4th rev. ed. (1974); Joseph D. Falcone, Principles and Practices of Residential Construction (1987); Francis D.K. Ching, Building Construction Illustrated (1975); Harold B. Olin, John L. Schmidt, and Walter H. Lewis, Construction: Principles, Materials & Methods, 5th ed. (1983), focusing on low-rise construction; and, for nontraditional building, Lester L. Boyer and Walter T. Grondzik, Earth Shelter Technology (1987).B.S. Benjamin, Structures for Architects, 2nd rev. ed. (1984), analyzes the behaviour of structural systems based on physical principles and properties of materials; Mario Salvadori, Why Buildings Stand Up: The Strength of Architecture (1980), is an illustrated introduction to structural engineering; and Mario Salvadori and Robert Heller, Structure in Architecture: The Building of Buildings, 3rd ed. (1986), is a broader survey of foundations and structural systems. See also Ronald C. Smith and Cameron K. Andres, Principles and Practices of Heavy Construction, 3rd ed. (1986); Irving Engel, Structural Steel in Architecture and Building Technology (1988); E. Eranti and G.C. Lee, Cold Region Structural Engineering (1986); and Wolfgang Schueller, High-Rise Building Structures, 2nd ed. (1986).The following works focus on building materials: Ronald C. Smith and Cameron K. Andres, Materials of Construction, 4th ed. (1988); Paul Bianchina, Illustrated Dictionary of Building Materials and Techniques (1986); Edward Allen, Fundamentals of Building Construction: Materials and Methods (1985); and Henry J. Cowan and Peter R. Smith, The Science and Technology of Building Materials (1988).Mechanical and electrical systems are studied in Richard D. Rush, The Building Systems Integration Handbook (1986); Building Services Research And Information Association, Building Services Materials Handbook: Heating, Sanitation, and Fire Protection (1987); Roger W. Haines, Control Systems for Heating, Ventilating, and Air Conditioning, 4th ed. (1987); Benjamin Stein, John S. Reynolds, and William J. McGuinness, Mechanical and Electrical Equipment for Buildings, 7th ed. (1986); and Robert H. Perry and Tyler G. Hicks (eds.), Building Systems Reference Guide (1987). Alfred Swenson Pao-Chi Chang Modern building practices Low-rise residential buildings Low-rise residential buildings include the smallest buildings produced in large quantities. Single-family detached houses, for example, are in the walk-up range of one to three stories and typically meet their users' needs with about 90 to 180 square metres (about 1,000 to 2,000 square feet) of enclosed floor space. Other examples include the urban row house and walk-up apartment buildings. Typically these forms have relatively low unit costs because of the limited purchasing power of their owners. The demand for this type of housing has a wide geographic distribution, and therefore most are built by small local contractors using relatively few large machines (mostly for earth moving) and large amounts of manual labour at the building site. The demand for these buildings can have large local variations from year to year, and small builders can absorb these economic swings better than large organizations. The building systems developed for this market reflect its emphasis on manual labour and its low unit costs. A proportion of single-family detached houses are factory-built; that is, large pieces of the building are prefabricated and then transported to the site, where considerable additional work is required to complete the finished product. Foundations All foundations must transmit the building loads to a stable stratum of earth. There are two criteria for stability: first, the soil under the foundations should be able to receive the imposed load without more than about 2.5 centimetres (one inch) of settlement and, second, the settlement should be uniform under the entire building. It is also important that the bottom of the foundation be below the maximum winter frost level. Wet soil expands as it freezes, and repeated freezethaw cycles can move the building up and down, leading to possible displacement and damage. Maximum frost depth varies with climate and topography. It can be as deep as 1.5 metres (five feet) in cold continental climates and is zero in tropical and some subtropical areas. The foundation systems for low-rise residential buildings are suitable for their light loads; nearly all are supported on spread footings, which are of two typescontinuous footings that support walls and isolated pad footings that support concentrated loads. The footings themselves are usually made of concrete poured directly on undisturbed soil to a minimum depth of about 30 centimetres (12 inches). If typical continuous concrete footings are used, they usually support a foundation wall that acts either as a retaining wall to form a basement or as a frost wall with earth on both sides. Foundation walls can be built of reinforced concrete or masonry, particularly concrete block. Concrete blocks are of a standard size larger than bricks and are hollow, forming a grid of vertical planes. They are the least expensive form of masonryusing cheap but strong materialand their large size economizes on the labour required to lay them. Their appearance and weathering properties are inferior to those of fired masonry, but they are satisfactory for foundation walls. In some places timber foundation walls and spread footings are used. Excavation for foundations is the most highly mechanized operation in this building type; it is done almost entirely with bulldozers and backhoes. Modern building practices Low-rise commercial, institutional, and industrial buildings The size of buildings in the commercial, institutional, and industrial market segment ranges from a few hundred to as much as 45,000 square metres (500,000 square feet). All of these buildings have public access and exit requirements, although their populations may differ considerably in density. The unit costs are generally higher than those for dwellings (although those of simple industrial buildings may be lower), and this type includes buildings with the highest unit cost, such as hospitals and laboratories. Residential buildings are fairly static in their function, changing only at long intervals. By contrast, most commercial, institutional, and industrial buildings must respond to fairly rapid changes in their functions, and a degree of flexibility is required in their component systems. In addition, these buildings are built by contractors who utilize heavy mechanized equipment not only for foundations (pile drivers and caisson augers) but also for lifting heavy components (a wide variety of cranes and hoists). Semimanual machines such as cement finishers, terrazzo grinders, and welding generators are also used, but a large percentage of the work is done manually; the human hand and back remain major instruments of the construction industry, well adapted to the nonrepetitive character of building. Foundations The foundations in these buildings support considerably heavier loads than those of residential buildings. Floor loadings range from 450 to 1,500 kilograms per square metre (100 to 300 pounds per square foot), and the full range of foundation types is used for them. Spread footings are used, as are pile foundations, which are of two types, bearing and friction. A bearing pile is a device to transmit the load of the building through a layer of soil too weak to take the load to a stronger layer of soil some distance underground; the pile acts as a column to carry the load down to the bearing stratum. Solid bearing piles were originally made of timber, which is rare today; more commonly they are made of precast concrete, and sometimes steel H-piles are used. The pile length may be a maximum of about 60 metres (200 feet) but is usually much less. The piles are put in place by driving them into the ground with large mechanical hammers. Hollow steel pipes are also driven, and the interiors are excavated and filled with concrete to form bearing piles; sometimes the pipe is withdrawn as the concrete is poured. An alternative to the bearing pile is the caisson. A round hole is dug to a bearing stratum with a drilling machine and temporarily supported by a steel cylindrical shell. The hole is then filled with concrete poured around a cage of reinforcing bars; and the steel shell may or may not be left in place, depending on the surrounding soil. The diameter of caissons varies from one to three metres (three to 10 feet). The friction pile of wood or concrete is driven into soft soil where there is no harder stratum for bearing beneath the site. The building load is supported by the surface friction between the pile and the soil. When the soil is so soft that even friction piles will not support the building load, the final option is the use of a floating foundation, making the building like a boat that obeys Archimedes' principleit is buoyed up by the weight of the earth displaced in creating the foundation. Floating foundations consist of flat reinforced concrete slabs or mats or of reinforced concrete tubs with walls turned up around the edge of the mat to create a larger volume. If these buildings do not have basements, in cold climates insulated concrete or masonry frost walls are placed under all exterior nonbearing walls to keep frost from under the floor slabs. Reinforced concrete foundation walls for basements must be carefully braced to resist lateral earth pressures. These walls may be built in excavations, poured into wooden forms. Sometimes a wall is created by driving interlocking steel sheet piling into the ground, excavating on the basement side, and pouring a concrete wall against it. Deeper foundation walls can also be built by the slurry wall method, in which a linear series of closely spaced caissonlike holes are successively drilled, filled with concrete, and allowed to harden; the spaces between are excavated by special clamshell buckets and also filled with concrete. During the excavation and drilling operations, the holes are filled with a high-density liquid slurry, which braces the excavation against collapse but still permits extraction of excavated material. Finally, the basement is dug adjoining the wall, and the wall is braced against earth pressure. Modern building practices Long-span buildings Long-span buildings create unobstructed, column-free spaces greater than 30 metres (100 feet) for a variety of functions. These include activities where visibility is important for large audiences (auditoriums and covered stadiums), where flexibility is important (exhibition halls and certain types of manufacturing facility), and where large movable objects are housed (aircraft hangars). In the late 20th century, durable upper limits of span have been established for these types: the largest covered stadium has a span of 204 metres (670 feet), the largest exhibition hall has a span of 216 metres (710 feet), and the largest commercial fixed-wing aircraft has a wingspread of 66.7 metres (222 feet) and a length of 69.4 metres (228 feet), requiring a 7580-metre- (250266-foot-) span hangar. In these buildings the structural system needed to achieve these spans is a major concern. Structural systems Structural types Structural systems for long-span buildings can be classified into two groups: those subject to bending, which have both tensile and compressive forces, and funicular structures, which experience either pure tension or pure compression. Since bridges are a common type of long-span structure, there has been an interplay of development between bridges and long-span buildings. Bending structures include the girder, the two-way grid, the truss, the two-way truss, and the space truss. They have varying optimum depth-to-span ratios ranging from 1 : 5 to 1 : 15 for the one-way truss to 1 : 35 to 1 : 40 for the space truss. The funicular structures include the parabolic arch, tunnel vault, and dome, which act in pure compression and which have a rise-to-span ratio of 1 : 10 to 1 : 2, and the cable-stayed roof, the bicycle wheel, and warped tension surfaces, which act in pure tension. Within these general forms of long-span structure, the materials used and labour required for assembly are an important constraint along with other economic factors. Modern building practices High-rise buildings The high-rise building is generally defined as one that is taller than the maximum height which people are willing to walk up; it thus requires mechanical vertical transportation. This includes a rather limited range of building uses, primarily residential apartments, hotels, and office buildings, though occasionally including retail and educational facilities. A type that has appeared recently is the mixed-use building, which contains varying amounts of residential, office, hotel, or commercial space. High-rise buildings are among the largest buildings built, and their unit costs are relatively high; their commercial and office functions require a high degree of flexibility. Foundations The foundations of high-rise buildings support very heavy loads, but the systems developed for low-rise buildings are used, though enlarged in scale. These include concrete caisson columns bearing on rock or building on exposed rock itself. Bearing piles and floating foundations are also used. Modern building practices The economic context of building construction Buildings, like all economic products, command a range of unit prices based on their cost of production and their value to the consumer. In aggregate, the total annual value of building construction in the various national economies is substantial. In 1987 in the United States, for example, it was about 10 percent of the gross domestic product, a proportion that is roughly applicable for the world economy as a whole. In spite of these large aggregate values, the unit cost of buildings is quite low when compared to other products. In the United States in 1987, new building cost ranged from about $0.50 to $2.50 per pound. The lowest costs are for simple pre-engineered metal buildings, and the highest represent functionally complex buildings with many mechanical and electrical services, such as hospitals and laboratories. These unit costs are at the low end of the scale of manufactures, ranking with inexpensive foodstuffs, and are lower than those of most other familiar consumer products. This scale of cost is a rough index of the value or utility of the commodity to society. Food, although essential, is relatively easy to produce; aircraft, at the high end of the scale, perform a desirable function but do so with complex and expensive mechanisms that command much higher unit prices which reflect not only the materials and labour required to produce them but also substantial capital and research investments. Buildings fall nearer to food in value; they are ubiquitous and essential, yet the services consumers expect them to provide can be supplied with relatively unsophisticated technology and inexpensive materials. Thus there has been a tendency for building construction to remain in the realm of low technology, for there has been relatively little incentive to invest in research given consumer expectations. Within this general economic context, there are a number of specific parameters that affect the cost of buildings. First are government building codes, which are enacted to protect public health and safety; these take the form of both prescriptive and performance requirements. Structural requirements include description of the loads buildings must support, beginning with the constant everyday loads of building contents imposed by gravity and extending to the less frequent but more extreme loadings of wind and earthquake forces. These are specified on a statistical basis, usually the maximum expected to occur with a 100-year frequency. Safety factors for materials are specified to allow for accidental overloading and lapses of quality control. Economic considerations are also reflected; for example, buildings must perform well under normal gravity loads, but no code requires a building to resist direct exposure to the wind and low-pressure effects of a tornado, for its cost would be prohibitive. Planning and zoning requirements provide for height and floor area limitations and building setbacks from lot lines to ensure adequate light and air to adjoining properties. Zoning regulations also establish requirements for permitted building usages, parking spaces, and landscaping and even set standards for the visual appearance of buildings. Another example is requirements for building atmosphere conditions; these include minimum (but not maximum) temperatures and rates of air change to dilute odours and provide an adequate oxygen supply. Life-safety requirements include adequate stairways for emergency exits, emergency lighting, smoke detection and control systems, and fire-resistant building materials. Sanitation requirements include adequate numbers of plumbing fixtures and proper pipe sizes. Electrical requirements include wire sizes, construction requirements for safety, and location of outlets. Beyond the government standards there are market standards, which reflect user expectations for buildings. One example is elevator systems; elevators are not required by building codes, but in the United States, for example, the number of elevators in office buildings is calculated based on a maximum waiting period of 30 seconds. Cooling of building atmospheres is also not required by code but is provided in climates and building types where the marketplace has shown it to be cost-effective. Building systems and components are perceived as having two dimensions of value. One is the purely functional dimension: the structure is expected to resist loads, the roof must keep out rain. The other is the aesthetic or psychic dimension: stone is perceived as more durable than wood; an elevator system with a waiting time of 30 seconds is preferable to one with a waiting time of two minutes. For these perceived differences many users are willing to pay more. When symbolic buildings such as temples, cathedrals, and palaces play an important role in society, the aesthetic dimension is important in valuing buildings; for example, the Parthenon of Athens or Chartres Cathedral commanded a level of investment in their economies that might be roughly compared to the U.S. Apollo space program. But in most buildings the functional dimension of value is dominant. Because of its relatively low level of technology, wide geographic distribution, highly variable demand, and wide variety of building products, the building industry in industrialized countries is subdivided into many small enterprises. This lack of centralization tends to discourage research and keeps building components sturdy and simple, following well-tried formulas. Within this diversity there are a number of fairly well-defined markets based on building types; these include low-rise residential buildings, low-rise commercial, institutional, and industrial buildings, high-rise buildings, and long-span buildings. A somewhat similar pattern is found in eastern Europe, although the building industry there is more centralized. There is also a much smaller low-rise residential market, with most new housing being provided in high-rise buildings. In developing countries the major market is for low-rise residential buildings to house rapidly growing populations. Much of the construction is undertaken by local craftsmen using simple building products. Local timber is widely used, and masonry materials still include the ancient mud brick. More sophisticated long-span and high-rise technologies are found only in major cities. Building design and construction Design programming The design of a building begins with its future user or owner, who has in mind a perceived need for the structure, as well as a specific site and a general idea of its projected cost. The user, or client, brings these facts to a team of design professionals composed of architects and engineers, who can develop from them a set of construction documents that define the proposed building exactly and from which it can be constructed. Building design professionals include those licensed by the statesuch as architects and structural, mechanical, and electrical engineerswho must formally certify that the building they design will conform to all governmental codes and regulations. Architects are the primary design professionals; they orchestrate and direct the work of engineers, as well as many other consultants in such specialized areas as lighting, acoustics, and vertical transportation. The design professionals draw upon a number of sources in preparing their design. The most fundamental of these is building science, which has been gradually built up over the past 300 years. This includes the parts of physical theory that relate to building, such as the elastic theory of structures and theories of light, electricity, and fluid flow. There is a large compendium of information on the specific properties of building materials that can be applied in mathematical models to reliably project building performance. There is also a large body of data on criteria for human comfort in such matters as thermal environment, lighting levels, and sound levels that influence building design. In addition to general knowledge of building science, the design team collects specific data related to the proposed building site. These include topographic and boundary surveys, investigations of subsoil conditions for foundation and water-exclusion design, and climate data and other local elements. Concurrently with the collection of the site data, the design team works with the client to better define the often vague notions of building function into more precise and concrete terms. These definitions are summarized in a building space program, which gives a detailed written description of each required space in terms of floor area, equipment, and functional performance criteria. This document forms an agreement between the client and the design team as to expected building size and performance.