Architecture curriculum

A plan is a horizontal cut through the building, usually taken about four feet above the floor so it passes through the windows, and it shows where every support stands. A section is a vertical cut that shows how spaces and objects are arranged one above another. An elevation shows one face of the building seen straight on, with nothing cut away.

Fenestration means the whole arrangement of a building's windows and openings, not any single one. Openings are read by their size, shape, location and materials, and one or more sides usually matter more than the rest simply because they are more visible. Changing the window sash is among the alterations that can damage a building's character for good.

A bay is one division of a long building whose successive parts are alike, such as the span between two piers of a nave with its own vault and windows. Its shape constrains everything above it: oblong vaulting bays forced medieval builders into awkwardly twisted vault surfaces. A module works the same way on paper, as one unit from which every other dimension is measured.

Proportion ties every part of a design to one chosen unit, so the parts keep fixed relations to each other and to the whole. Vitruvius drew the idea from the human body, where forearm, foot and palm agree, and set a temple's dimensions from the thickness of a column. The size and proportion of a room are among the qualities that give it character.

Massing is the building's overall shape: its volumes, its roof and roof features such as chimneys, and projections such as porches and bay windows. You read it first, from a distance and by walking around the building, before looking at any detail, because these broad aspects carry much of a building's character on their own.

Circulation is the route people take through a building, and the sequence of spaces along it can matter more than any single room, especially where a strong central axis organizes the plan. The program is the set of uses the building must house. Vitruvius judged convenience by whether the arrangement of rooms got in the way of use.

Vitruvius held that every building must answer to durability, convenience and beauty, and he gave each a test. Durability rests on foundations carried down to solid ground and well-chosen materials, convenience on rooms arranged without hindrance, beauty on members in due proportion. A later definition keeps the pairing: a structure built for strength and stability alone is engineering, not architecture.

Dead load is the weight of the structure itself: its walls and frame plus the floor and roof slabs each member holds up. Live load is the weight of what the building contains, such as furniture, equipment and files, and it shifts as rooms are rearranged and uses change. The balance varies: in heavy masonry the dead load is so large that the live load barely changes the risk of failure.

An earthquake pushes a building sideways, and a structure that holds its weight up well may still lack the overall strength and stiffness to resist that push; many older buildings were never designed for it. Plan matters too: a regular plan resists equally in every direction, while an irregular one has uneven strength and stiffness. A ground floor with big openings and few walls can become a weak story.

Sideways forces need a positive, continuous path through the building into the foundation and the soil, so every piece must be connected to the next: cladding to frame, joists to beams, walls to floors and roof, columns to footings. A break anywhere makes the whole system ineffective. In old masonry, walls that merely rest against the floors are pulled apart by shaking, so tying them together is among the most effective fixes.

Each way of spanning stresses its material differently: a suspension cable is stretched, an arch of wedge-shaped stones is squeezed, and a beam is both, its upper side shortened and its underside lengthened as it bends. That is why plain concrete, weak in tension, works best squeezed, and why a concrete beam needs steel bars placed to take the tensile stresses that bending creates.

A frame is stiffened against sideways force with diagonal braces that let it act as a truss, with shear walls that resist force in their own plane, or as a moment frame whose rigid beam-to-column joints resist by bending. Braced steel frames perform especially well in earthquakes; moment frames are more flexible, so they sway more between stories and can pound against neighbors.

A foundation passes every load into the ground, and its weakness can lie in the foundation itself or in the soil beneath it, which can fail outright, as when shaking makes it liquefy. Remedies range from upgrading a footing to adding piles or drilled piers. In light wood houses the critical link is anchorage: a frame not bolted down can slide right off its foundation.

Progressive collapse is a chain reaction: a local failure spreads from member to member until the damage is out of proportion to its cause. A structure resists it either by giving key members enough strength to survive, or by alternate paths, so that a lost member's load passes to neighbors with the strength and continuity to carry it. A statically determinate structure, the most efficient in theory, has no alternate path.

A lintel works by resisting bending across its length, which stone does poorly. Vitruvius warned that widely spaced columns risk breaking their stone architraves, and that the widest spacing had to use wooden beams instead. Roman builders later stretched the limit by assembling a lintel from wedge-shaped stones, a flat arch, with a discharging arch above to take weight off its center.

Corbelling closes an opening by letting each course of stone overhang the one below until the two sides meet. Because the beds stay horizontal, the result is a vault or dome only in form, and it exerts no outward thrust. A true dome differs in having each course pitched to follow the curve, which is what lets it carry load as an arch does.

A true arch is built of voussoirs, wedge-shaped stones set radially, so each one is squeezed between its neighbors. That compression travels round the curve to the supports, where it arrives as both weight and an outward push. Stones laid in flat, overhanging courses can imitate the shape without working this way, so look at the joints, not the outline.

An arch or vault pushes outward on its supports as well as down, and that thrust has to go somewhere. It can be met by sheer mass, in thick walls and heavy abutments, or opposed by the counter-thrust of neighboring arches and vaults. Roman builders mostly relied on mass; Gothic builders balanced thrust against thrust. A buttress is the mass placed specifically to take that push.

A barrel vault keeps the same cross-section along its length, so it presses on the whole length of both walls and windows must stop below where it springs. A groin vault, made where two barrel vaults cross, gathers its weight and thrust onto the corners instead. The walls between are freed, and windows can rise to the full height of the vault.

Roman domes nearly always sat on a circular wall rising from the ground. To put a dome over a square, builders set it on four arches spanning the sides and filled each corner with a pendentive, a curved triangle of masonry that turns the square into a round base. A squinch does the same job with a small conical vault across each corner, producing an octagon first.

Arches and vaults are normally raised over temporary timber centering that carries them until they are complete. Smaller Roman vaults were cast in concrete over molds of rough boards. Nineteenth-century studies argued that Byzantine builders avoided centering where they could, using large, thin, flat bricks that could be stuck against work already built, so vaults rose with little support.

In a skeleton frame, steel columns and beams carry the building, so the outer wall no longer has to. That wall becomes a curtain wall: self-supporting, hung on or attached to the frame, carrying none of the building's weight, and free to be mostly glass or thin panels. Skeletal steel construction dates from the nineteenth century and was central to the rise of high-rise buildings.

A truss is a framework whose members are each arranged to resist mainly tension or mainly compression, so together they act like a deep beam or arch. Compression members tend to buckle, which is why they are best kept short: one bridge pattern patented in the 1840s put its shorter web members in compression and longer ones in tension, greatly reducing the risk of buckling failure.

A cantilever is supported at one end only, so all its load must be resisted where it is held: bending is zero at the free tip and greatest at the support. An overhang therefore depends on how firmly its root is fixed, as in a retaining wall built as a slab cantilevered from its base. The action can also appear by accident: early concrete girders cracked during lifting because their unsupported ends worked as cantilevers.

A shell is a curved surface that gets its strength from its shape rather than its bulk. Masonry domes show the idea: Byzantine builders sometimes formed a dome with flat ribs or ridges of the same material, stiffening the shell by its form rather than adding separate ribs, and later builders split great domes into two shells, an inner one for the interior and an outer one for the skyline.

A cable or chain can only pull: a suspension bridge's supporting structure is stretched by its load, where an arch is squeezed. So everything depends on what holds the ends, and an engineer of 1910 warned that a suspension bridge should never be built where a sound anchorage cannot be found. Cables are also flexible, and swaying set up by marching soldiers or gusts of wind has brought some suspension bridges down.

A hall without interior supports can be roofed by vaulting, by trusses or by suspension, and each pays for its span differently. Roman vaults produced open interiors no arrangement of piers and columns could match, at the cost of heavy thrust. Trusses suit very wide spans and became the typical modern answer, and glued-laminated timber arches and trusses roof many mid-century arenas.

All steels lose strength as they heat: by 600 degrees Celsius most structural steels have lost more than half of it, and above 500 degrees creep erodes their load-carrying capability further. So steel in buildings is insulated to keep it cool in a fire. Code changes drawn from a federal investigation of high-rise collapses grouped spray-applied fireproofing and redundant sprinklers with resistance to collapse in fire.

Ashlar is stone cut into squared blocks; rubble is uncut stone laid at random. Roman builders often combined them, facing a wall with ashlar and filling the core with rubble set in cement. Stone was usually laid in mortar but sometimes dry-stacked without it. In early Greek walls, irregular polygonal blocks and regular courses were used side by side until coursed work won out.

A bond is the pattern that locks a masonry wall into one mass, since two faces not tied to each other should never be built. A builder's manual of the 1920s counted only two true brick bonds, English and Flemish; running bond, it said, is no bond at all, so a face laid that way had to be tied to its backing with hidden diagonal headers and metal anchors. Common bond adds a course of headers every sixth course.

Historic mortar was mostly soft lime and sand. Portland cement, which makes a more rigid mortar, was made in the United States from the early 1870s but came into common use only in the early twentieth century. Repointing should match the old mortar's strength and composition, because hard, high-cement mortar in soft nineteenth-century brick can make the brick itself spall. Lime mortar is also more flexible.

The old braced frame joined heavy timbers in the European tradition. The balloon frame replaced it with light, standard-size studs nailed together, quick to build but flimsy and fast to burn, with studs running unbroken past the floors. The platform frame builds each floor as a deck for the walls above, curing the uneven settlement of earlier frames and freeing upper windows from lining up with those below.

Adobe is sun-dried brick that was never kiln fired, cob is a mix of shale, clay, straw and water built up in layers, and pise is earth rammed between forms. All are durable only when kept dry. Water rising from the ground erodes and bulges an adobe wall, and hard cement stucco or patches make things worse because they trap moisture behind them and move differently from the earth.

Until the late nineteenth century, stucco and plaster were mostly lime, sand and water, often with straw or animal hair as a binder, and Portland cement then made them harder. Traditional masonry is easily damaged by coatings that stop moisture from leaving. Water repellents belong only where repair has failed to stop water, and one waterproof coating trapped water from a leaking roof until part of a parapet failed.

Uncontrolled moisture is the most common cause of decay in older buildings, driving erosion, corrosion and rot until structure itself is lost. A weather-tight roof is therefore the first line of defense, and gutters, flashings and drainage carry the rest. Traditional buildings also handled air: cupolas and roof lanterns let warm air rise and drew a natural draft through the rooms.

Structural cast-iron columns came into use in the 1820s, followed by whole cast-iron fronts, and their slender columns and lintels let storefronts hold larger sheets of glass. Cast iron's weakness is a lack of toughness: short of tensile strength, a long column carries only a small fraction of what a short block of the same metal bears. Wrought iron, the first iron used in America, served mostly as nails, tie rods and straps until the mid-1800s.

Steel came into its own as manufacturing improved in the mid-nineteenth century, and structural steel was central to the rise of high-rise buildings. Frame members are joined by angles and plates that may be riveted, welded or bolted. Its asset is ductility, the ability to keep deforming without breaking when loaded past capacity; the cost of a flexible frame is large sway between stories.

Plain concrete has little tensile strength, which is why steel bars are embedded to take the tensile stresses that bending creates, placed on the side that is pulled; by the early 1900s engineers were already arguing over how best to arrange them. The usual failure is corrosion: when the bars rust, the concrete around them spalls, so a repair first cuts back the damaged concrete to remove the source of decay.

A curtain wall carries only itself: it is hung on or attached to the frame and holds none of the building's weight. Cheap plate glass made such walls possible, and by the mid-twentieth century glass cladding and curtain walls were nearly synonymous. The cost is thermal: a historic wall that is under a fifth glass loses little heat through its windows, but insulated glass was not readily available until about 1950.

Engineered wood is made by gluing smaller pieces of wood into larger members. Glued-laminated timber, or glulam, bonds layers of lumber, has been made since the 1930s, and often forms the arches and trusses of column-free arenas. In fire, large glulam members char on the outside and the char protects the wood within; tested columns earned three-hour ratings, and cross-laminated timber now frames buildings twenty-five stories tall.

Showing or hiding structure is a design decision with a history. Exposed iron and steel define the open interiors of nineteenth-century train sheds and armories, exposed wood framing became decoration in Arts and Crafts houses, and exposed cast concrete gives many industrial interiors their character. A concealed structural system may still matter as building technology even though it plays no part in how the building looks.

In flat Mesopotamia, with sun-dried brick as the main material, tall buildings were impractical, so height came from setting temples on huge stepped terraces of crude brick faced with fired brick or stone. Thick walls gave stability and shelter from the heat. Without stone columns or long beams, broad halls were impossible, so palaces read in plan as long corridors and small rooms.

A mastaba is a rectangular tomb of stone or brick with gently sloping sides and a flat top, so that from a distance it can pass for a cut-off pyramid. A pyramid's plan keeps the mastaba's leading features. Some early pyramids were built as stacked stages, one in six great steps with inclined faces, and one at another site has a broken slope, steeper below than above.

Egyptian building was almost entirely lintel construction, and a stone lintel spans only a short gap, so any room too wide for single lintels needed rows of piers or columns. The great columnar halls turned that limit into effect through sheer height, mass, number and painted decoration. A taller central aisle with clerestory windows above the side roofs let light into the dim interior.

An Egyptian temple lined up its parts along one route: an avenue of sphinxes, a gateway between twin pylons, an open court, a columnar hall and finally the sanctuary. The roofs stepped down from front to back, and the innermost chambers were low, dark and open only to priests and king. Later kings lengthened temples by adding courts and halls to the front, so at one great temple the outermost gateway is the last one built.

Egyptian capitals came in a handful of plant-derived types: the closed lotus bud, single or clustered; the open bell; the palm; and a block carved with the face of Hathor. Columns were stout, seldom more than six diameters tall, often narrowed at the base, and painted all over with lotus and papyrus motifs, so they read as symbols as much as supports.

The great Egyptian monuments are records of logistics. Stone was often blocked out before it left the bedrock, and one granite obelisk still lies in its quarry with its underside joined to the rock. Riverside quarries loaded blocks straight onto barges, canals brought boats to distant cliffs, and overland the stone moved on sledges drawn by oxen or hauled by gangs on rollers.

The Greek Doric column stands directly on the platform with no base, its sharp-edged flutes rising to a plain cushion capital under a square slab. Above, the frieze alternates triglyphs, blocks with vertical grooves, and square metopes. That rhythm has a catch at the corners: a triglyph cannot sit over both the corner column's center and the very end of the frieze, so builders narrowed the end spacing.

Ionic columns are far slimmer than Doric, eight to ten diameters tall against roughly four to seven, and stand on a molded base. The capital carries a band that ends in a scroll, or volute, at each side, and the frieze runs unbroken, often carved in relief. The volutes show a different face from the side than from the front, an awkward fact at the corner of a colonnade that builders never fully solved.

Corinthian began as a variant of Ionic: in pure Greek work its entablature was the same, and only the capital was new, a tall bell wrapped in one or two rows of acanthus leaves with scrolls rising to the corners of a concave-sided abacus. The Greeks used it mainly on small monuments; it was the Romans who developed it fully. Vitruvius told a legend of acanthus growing round a basket left on a grave.

A Greek temple's core was the cella, a windowless chamber for the cult statue entered through a columned porch. Plans are named by how columns are added: in antis has columns between the projecting side walls, prostyle a porch in front, amphiprostyle porches at both ends, peripteral a colonnade all round, dipteral a double one. Unlike Egypt, the columns stood outside the solid wall rather than enclosed by it.

In the finest Greek temples the apparently straight lines are subtly curved: the platform and cornice rise slightly toward the middle, the columns lean almost imperceptibly inward, their profiles swell gently outward, and the corner spacing is a little tighter. Vitruvius gave one reason: corner columns seen against open sky look thinner than they are, so they should be made thicker to counter the illusion.

The entablature is everything above the columns, in three bands: the architrave resting directly on the capitals, the frieze, and the projecting cornice. The frieze is the quickest clue to the order: Doric divides it into triglyphs and metopes, while Ionic and Corinthian run it continuous, often with carving. An Ionic architrave is also usually stepped in two or three flat bands rather than left plain.

Greek forms returned near the close of the eighteenth century, and Doric and Ionic columns were soon applied to every kind of building. In the United States the revival peaked around 1830 to 1840, shaping federal buildings and several state capitols and filling towns with brick and wooden houses fronted by Greek porticos.

Pozzolana, a volcanic powder from southern Italy, mixed with lime and rubble makes a cement that sets hard even underwater. With it the Romans no longer had to cut every block: walls could be faced with brick or cut stone and filled with concrete laid in layers, and unskilled labor could raise vast vaulted buildings quickly and cheaply.

Rome made the arch and vault the basis of its whole system and used them at a scale no earlier builders had tried, in bridges, aqueducts, baths and basilicas. Barrel vaults covered corridors and long halls, groin vaults gathered weight onto piers, and domes rose over circular walls. Thrust was handled with masses of masonry set at right angles to the hall wherever the vaults pushed.

The Pantheon's hemispherical dome rests on a circular wall about twenty feet thick, and its only light comes through one round opening at the crown. Deep rectangular coffers pattern the inside of the dome. Recesses fronted by columns hollow out the great wall, lightening it without weakening it, and a gabled porch of granite columns stands in front of the round hall.

The Roman basilica was a hall for law and business: a wide, tall central nave flanked by lower aisles, lit by clerestory windows above the aisle roofs, and ending in an apse where the magistrates sat. Vitruvius sized it so the aisle was a third the width of the central space. Christians later took over the type, adding a transept across the far end.

Roman builders kept the Greek orders but often stopped using them as supports. Engaged columns, built into the wall and projecting more than half their diameter, were set between the arches of many-storied arcades, with entablatures marking each floor. Critics call the column superfluous there; defenders note that it gives light and shade and states the piers' vertical work.

Roman cities ran on engineered systems. Vitruvius had water brought in solid masonry channels on a steady gentle slope, roofed over so the sun never struck it, then into a city reservoir that fed fountains, baths and houses from separate tanks. In the capital, forums and a network of colonnades gave citizens monumental public space and sheltered routes across large tracts of the city.

Greek theaters were usually cut into hillsides, but the Roman amphitheater stood free, its tiers built up of stone and concrete and wrapped in stories of arcades. Vitruvius gave the planning rule for such crowds: many spacious entrances, upper levels kept separate from lower, and straight passages without turns, so that people leaving a show are never crowded together.

Early Christians took over the Roman basilica nearly unchanged: a tall nave lined by columns, lower aisles about half its width and height, a clerestory, a timber roof, and an apse at the far end for the clergy, with the altar before it. A colonnaded forecourt, the atrium, often came first, its inner side forming a porch called the narthex. Plain outside, these churches were rich with marble and mosaic within.

Circular and polygonal plans had long served tombs and baptisteries, and their adoption for churches was the first real break from the basilica. In two sixth-century octagonal churches, a domed central space is ringed by an aisle, and semicircular niches push out from the center to enlarge it, an idea traced back to the niches of the Pantheon.

Its central dome rests on four great arches over a square, and two of those arches open into half-domes that step down toward each end, so the space builds up to the summit through a sequence of curves. A ring of forty windows pierces the base of the dome, so light enters exactly where the dome begins. Massive buttresses divide the aisles, and the church has survived many centuries of earthquakes.

Both put a dome over a square. A pendentive is a curved triangle cut from a sphere; its courses rise from four arches and meet in a complete circle, so the transition is one smooth surface with no corners. A squinch spans each corner with a small conical vault or niche, giving an octagon first, so you see a stepped, faceted transition. Squinches appear from Persian domes to medieval crossings in Spain.

Byzantine churches were plain outside and made their effect within through color rather than carving. Mosaic of colored glass, usually on a gold ground, covered the vaults and the wall above their springing, with the richest figures in the half-dome of the apse. Below, the walls were sheathed in panels of veined marble laid so the veining formed symmetrical patterns.

In the typical later Byzantine church, the ground plan is a square with four columns inside it, while above, the vaults form a cross of four equal arms with a dome over the center. Reducing the dome's supports to slender columns made a compact, centralized church. Later churches lifted the dome on a drum pierced by tall windows to bring in more light.

The earliest great mosques were simple one-story halls with flat wooden roofs carried on parallel rows of columns and arches, the arcades closing one side of a square court or ringing it entirely. Their effect came from long perspectives down the aisles rather than height: one Spanish example covers a vast area yet stands only about thirty feet high. The hall is oriented by a niche marking the direction of prayer.

A mosque needs remarkably little: a court with a fountain for ablutions, a prayer hall with a niche, the mihrab, set in the wall that faces the direction of prayer, and a tall, slender pulpit, the minbar, for reading the Quran. From inside, the mihrab tells you which way the building faces. The minaret, from which the call to prayer is given over the city, was added by the ninth century and is the element read from outside.

Arch profile places a building quickly. In Egypt and Syria the pointed arch was used almost everywhere. In North Africa and Spain builders preferred horseshoe and cusped arches, often with voussoirs in alternating colors. Persian work adds the ogee, an arch of two reversed curves meeting in a point, and older Persian palaces had huge horseshoe-shaped entrance arches.

Muqarnas, often called stalactite work, is built up from tiny corbels combined with rows of small niches, multiplied into intricate geometric tiers. It is used where one surface gives way to another: in the pendentives beneath domes, in the hoods of great doorways and niches, and in the brackets that carry the projecting galleries of minarets.

Islamic ornament works in three related systems: interlaced star-and-polygon geometry, flowing vine and floral patterns, and inscriptions in Arabic script woven into the same field. Doors, pulpits and pavements were framed in geometric star panels. Regional taste differs: Egyptian work leans toward intricate geometry, while Persian decoration prefers flowing lines and floral motifs in blended, more subdued color.

Islamic houses and palaces turn inward. They are built around one or more courts and show the street an almost unbroken wall, with the main court centered on a fountain and a raised, vaulted reception room opening onto it. The mosque court has its fountain for ablutions. In Mughal India the setting itself became design: platforms, courts, gateways and gardens frame the great tombs.

A stupa is a domed mound built over relics or to mark a sacred spot and once crowned by a small shrine-shaped finial. What you move through is around it: a carved stone railing with gateways encloses the mound, and some great stupas rise from stepped terraces that served as paths for walking in procession around the monument.

The core of a Hindu temple is a small, windowless shrine cell under a tall tower, with porches and halls leading up to it. In the north the tower rises on a curved profile, often clustered with smaller copies of itself and capped by a melon-shaped stone. In the south the sanctuary is often low, while towering gateways mark the walled enclosures around it, so the tallest structure may be an entrance rather than the shrine.

Rock-cut buildings are carved out of a cliff rather than assembled. Early Buddhist halls were hollowed into hillsides as a nave ending in an apse, with a roof shaped like a barrel vault and a small stupa at the far end, and their carved fronts copy timber construction. Later builders went further and carved whole freestanding temples from the living rock, imitating built designs.

Chinese and Japanese buildings are framed in timber, with ingenious joinery and bracketing beneath broad eaves and heavy tiled roofs that slope down in a curve. Because posts and beams do the carrying, the walls need not: a Japanese house may have two or more sides with no permanent wall, and its rooms are divided by light sliding screens running in grooves.

A pagoda is a tower of diminishing stories; one celebrated fifteenth-century Chinese example, now lost, was nine stories high and polygonal. Like the stupa, it belongs to Buddhist practice, and in Burma the name is given to great relic monuments, dagobas, each crowned by an iron spire. Stacked stories are the clue that separates the tower form from the domed mound.

Japanese floor mats were made to a near-standard size, about three feet by six, and a plan names each room by how many mats it holds, so the mat sets the dimensions of the room and even the lengths of lumber. Partitions are light sliding screens in grooves; slide them back or lift them out and several rooms become one, so the plan changes with use.

In West African earthen towns, walls were built of sun-dried brick set in mortar and finished with a special coat of mud plaster. Rain wears that coat away every wet season, so the buildings last for centuries only through steady repair, and that repair consists of renewing the plaster rather than rebuilding the wall.

Great Zimbabwe, in southern Africa, is a city of drystone walls, stone laid without any mortar. Walled groups of buildings stand on the hill and in the Great Enclosure and the valley enclosures, with ordinary homesteads on unwalled ground between the clusters of walls. Gold-working remains on the hill date to the eleventh and twelfth centuries, and those in the valley to the thirteenth through seventeenth.

A Mesoamerican pyramid was above all a platform: every important building stood on a terrace or truncated pyramid that took far more labor than the temple it carried. Built of earth and stone faced with masonry and stucco, it was climbed by a stair to a shrine on top, and many grew by accretion, an older building filled solid to support a new one above.

The alcoves form naturally: water seeps through porous sandstone, stops at a shale layer, freezes and breaks the rock loose. Builders shaped sandstone blocks with harder river stones and set them in a mortar of soil, water and ash, packing gaps with small stone chips. Many visitors read the dwellings as forts, but most scholars point to water: they sit near seep springs.

A Plains tipi starts as a frame of three or four lashed poles; more poles, often fifteen to twenty-five, are added before a cover of sewn buffalo hides goes on, and the whole could be dragged by horse or dog. Compare the permanent earthlodge of the same region: a sod-covered timber frame thirty to sixty feet across, rebuilt about every ten years. Mobility and permanence produced opposite structures.

Before mechanical systems, buildings met climate with their own fabric. In cold places windows were kept to what light and air required; in hot places many windows gave ventilation, while wide overhangs, awnings and shutters cut heat gain. Thick masonry walls hold heat and release it slowly, keeping rooms cooler in summer and warmer in winter, and cupolas drew air through the building.

Outside a few southern French churches, the Romanesque arch was always round. Walls were heavy, often rubble between facings of axe-dressed stone, and windows and doors were splayed wide to let light through their thickness. Buttressing was mostly internal and tentative, so the walls themselves had to hold the vaults, which kept windows small and exteriors plain.

Romanesque builders wanted churches that would not burn, which meant replacing timber roofs with stone vaults. A barrel-vaulted nave pushes outward along its whole length, and builders met it with half-barrel vaults over the aisles leaning against massive outer walls, at the cost of the clerestory. Where they raised the vault for windows, even giving it a pointed section to cut the thrust, most of those early vaults fell in.

Romanesque naves were divided into bays by their piers, which were usually clustered and, under square bays of four- or six-part vaulting, alternated heavier and lighter. From the eleventh century one or more shafts of each compound pier ran up to carry the vault ribs, so the bays read clearly from floor to vault, while a triforium marked a three-part division of the wall's height.

An ambulatory continues the choir aisle around the apse, often with chapels radiating from it. The first ambulatories were probably built in churches holding a revered relic, as a corridor that let pilgrims circle the altar where relics were shown without crossing the choir. Vaulting that curving aisle was hard, because each section of its plan is a wedge, not a rectangle.

A tympanum is the flat field between a doorway's lintel and the arch above it. On Romanesque churches the western porches and portals were the most important parts of the exterior, deep with massive arches, clustered piers and carved moldings, so the tympanum over the door became the place for sculpture. Gothic builders kept the idea, carving scriptural scenes over their central doors.

Read the structure, not just the arch. Romanesque churches are lower and massive: semicircular arches, heavy walls pierced by few openings, and buttressing kept mostly inside. Gothic churches concentrate their loads on piers and flying buttresses, turn the wall between into glass, and grow taller and slimmer in every part. A pointed arch alone settles little: some Romanesque vaults were pointed, and Gothic is defined by its system.

When a narrow semicircular vault meets a wide one, it cannot rise as high, so the two either penetrate awkwardly or meet in wavy, hard-to-build groins. Giving the arches a pointed profile lets a narrow vault rise as high as a wide one, so vaults over oblong bays meet in clean, plane-curved groins. The pointed arch then spread from the vault ribs to windows and pier arches, which had to fit beneath them.

Instead of building a whole groin vault at once over full timber centering, builders first raised a skeleton of stone ribs: two along the walls, two across the nave, and two along the diagonals. Each of the four compartments between them could then be built separately on light centering carried by the ribs. The builder chose each rib's curve, and the thin vault surfaces were warped to fit, the ribs serving as guides.

Gothic builders met vault thrust with counter-thrust rather than mass: flying half-arches carry the push across the aisle roofs to tall external buttresses, often weighted by pinnacles. The system works only as a chain. One medieval designer set a flying buttress's column on a corbel with no solid bearing, so the failure of a single course in the pier would break the buttress on which the main vault depended.

Once vaults gathered their loads onto isolated piers and buttresses, the building stood as if on legs and the wall became mere infill, which could then be almost entirely suppressed. Huge stained-glass windows took its place; in one Paris chapel, deep buttresses take every thrust and the spaces between are wholly window. Stained glass in turn pushed builders toward ever larger openings and finer tracery.

Tracery is the stonework that holds the glass of a large window, and its style is the quickest way to date a Gothic building. Early plate tracery pierces simple circles and foils through solid slabs; bar tracery thins the stone into molded ribs in geometric patterns, the age of great rose windows; late work flows into flame-like curves in France or rigid vertical panels in England.

Every Gothic device pushes the same way: upward and toward light. Compared with Romanesque work, the clerestory grows lofty, a triforium gallery runs beneath it, pier arches rise high and pointed, slender clustered shafts multiply, and the piers themselves shrink in area. Outside, towers and spires on the front, and sometimes over the crossing, carry the same emphasis into the skyline.

French cathedrals ring the apse with an ambulatory and radiating chapels. English ones are long and narrow, often with a square east end and secondary transepts, and late English vaults spread into fans. Italian builders kept thick walls, small windows, marble veneer and often the round arch, tying their vaults with iron rods rather than deep buttresses. In the United States a Gothic revival ran from about 1840 to 1875, chiefly in churches.

Early Renaissance builders used the Roman orders loosely, as carved pilasters with invented capitals; after about 1490, classical detail was copied with increasing fidelity. Either way the order was mostly dress over a hidden frame, so read a Renaissance pilaster as decoration, not as the thing carrying the load.

Proportion here means relation, not size: one chosen part, such as a column's thickness, sets the measure of every other member, so the design keeps its look at any scale. The ancient canon for the orders, set down as rules by Vitruvius, was revived in more detailed and precise form by Vignola in the sixteenth century. Two buildings of very different size can share one set of proportions.

In Vasari's account, Brunelleschi worked out a method for true perspective by tracing it from the ground plan and the profile with intersecting lines, then proved it by drawing real Florentine buildings. The tie to architecture is that method: perspective was built from the same plan and elevation an architect draws.

Florence's cathedral left an octagon about 143 feet across, and roofing it seemed to need a vast, costly timber framework. In Vasari's account the winning plan built two shells, tied by ribs, without framework for the first thirty braccia, while critics warned a double vault would be too heavy. The form copies no Roman model, though study of Roman vaults made it possible.

The Florentine palace set a type: a rectangular block of rough, fortress-like rusticated stone, mullioned windows in two upper stories, and a huge classical cornice, wrapped around a courtyard ringed by light columned arcades. The contrast is deliberate, stern outside and open within. Later palaces kept rustication only at the base and corners.

Palladio's illustrated Four Books carried his designs far beyond Italy. In colonial America, what set Georgian houses apart from earlier Colonial ones was classical detail plus a balanced plan, symmetrical in outside massing and in room arrangement alike; in its more Palladian phase the arch survived mainly as the middle opening of the Palladian window. By that test, a classical porch on an informal plan does not make the type.

Renaissance design spread through books as much as through buildings. Vitruvius's ancient treatise supplied rules, and sixteenth-century authors such as Vignola and Palladio gave the movement a written and drawn form that could travel. Palladio's fourth book, on the ancient temples of Rome, let readers far from Rome study those buildings on the page.

Baroque facades treat the classical vocabulary as material to bend rather than rules to obey: broken pediments, huge scrolls, colossal orders and florid stucco. Nineteenth-century critics trained on Renaissance rules saw only disregard for propriety, which shows how far the departures went. Read them as chosen effects, not as mistakes in applying the rules.

An oval keeps a centralized plan but stretches it along one axis. In the sixteenth century, Vignola's earliest church already covered a small oblong room with a dome of oval plan, modeled on an ancient Roman dome but drawn out; Baroque builders carried the ellipse further, as in the elliptical staircase of Rome's Barberini palace. The shape itself was old, since Roman amphitheaters were elliptical.

Light can be designed like a material: where it enters decides the effect. Domed churches long controlled it from above. One famous early church rings the base of its dome with forty windows, and later, smaller churches raised a tall drum under the dome so longer windows could admit more light. Find the source first; the contrast it makes is the effect.

In seventeenth-century Rome, many open squares were given fountains, some backed by elaborate architecture, where sculpture, moving water and building are composed as one piece and set into the city. Asking whether such a work is architecture or sculpture misses the point: the blurred boundary between the arts is the design.

Baroque Rome was planned in views. A fresco records Pope Sixtus V's intended thoroughfare with an obelisk at each end of the vista, a plan he later dropped, and at St. Peter's a vast forecourt lined by colonnades was added in the 1660s to stage the approach. The street, the square and the marker at its end were composed together, like a set.

In French rooms of the Louis XV period, the rococo or rocaille manner brought wavy lines and abundant carving. Yet the main lines of a room seldom followed that movement: doors, openings and the plans of panels usually stayed straight and generally symmetrical. That is the discriminator, since rococo curls the ornament laid over a regular room rather than the room itself.

Neoclassicism answered Rococo extravagance by copying ancient models literally, such as Roman arcades and porticos. Restraint is the tell: GSA separates its twentieth-century Neoclassical buildings from Beaux-Arts ones because they carry columned porticos without enriched moldings and statuary. A nineteenth-century critique adds a caution: a correct antique front can become a frontispiece with the rooms fitted behind it.

The Roman revival came first; the Greek revival followed late in the 1700s, once newly published discoveries of Athenian monuments made Greek Doric and Ionic columns fashionable. France kept to Roman models, finding Greek forms too severe for modern needs. In the United States the Greek manner, which GSA says evoked the democratic ideals of ancient Greece, dominated public building from about 1820 to 1860.

In Britain, a circle of students of medieval buildings, Pugin among them, pressed in the 1830s for reviving Gothic as the national architecture. Pugin and Ruskin also gave the case a moral form: design choices are ethical choices, with honest expression of structure as a duty. In the United States the revival ran roughly from 1840 to 1875 and was used mostly for churches.

Early nineteenth-century designers attached a meaning to each historic vocabulary, Grecian, Egyptian, Italian or castellated, and chose among them by an agreed code according to the type of building. That code is what separates eclecticism from confusion. Later critics complained when the choice lost its reasons and forms were piled together without regard to what each signaled.

The Paris Ecole des Beaux-Arts taught Roman principles of design, and Americans trained there brought them home late in the 1800s. The method shows in plan first: monumental, formal planning, symmetrical facades and monumental stairs, and at city scale the City Beautiful movement's formal relationships between monumental buildings. A classical skin over an informal plan is not Beaux-Arts.

Late nineteenth-century American libraries, state capitols and federal buildings used classical language to look permanent and public. One Indianapolis courthouse of 1905 lines its front with three-story Ionic columns, heroic sculptures and a heavy cornice. Its risk is the one critics saw in the Roman revival: splendor won for the street at the expense of convenience inside.

London's 1851 exhibition hall covered eighteen acres in about four months, using some 900,000 square feet of sheet glass. Its designers aimed for extreme simplicity because time was short, and for a form that could be reused for other purposes afterward. Speed, repetition and reuse were the design brief, not afterthoughts.

A big terminal is two buildings in one: a masonry head building in a historic style, and behind it a train shed of slender columns and trusses roofed with glass, because no ancient model covered tracks. A 1918 critic found New York's Pennsylvania Station's latticed steel columns cutting through granite cornices, the two systems never fused.

The tall office building answered four pressures at once: fireproof construction, well-lit offices, the passenger elevator, and costly land in crowded business districts. Its later examples rest on a frame of iron or steel columns and beams, so the outer wall is only infill. Read it as a combination: no single invention produced the type.

Early skyscrapers split on how to show the frame. Chicago designers ran slender piers unbroken from base to top, while many Eastern ones dressed the frame as ordinary masonry. Louis Sullivan called his own early attempts his "masonry" period, then treated the wall as a terra-cotta casing that lets the steel be felt through it.

Read in its early context, the slogan described growth, not austerity: a 1918 writer called a building organic when its form follows its function, changing as that changes, rather than wearing a borrowed mask. The same writer praised a steel frame wrapped in a terra-cotta casing, so reading the phrase as a ban on ornament or cladding misreads it.

Arts and Crafts writers of the 1890s blamed machinery driven by competition for divorcing beauty from use and smothering objects in meaningless ornament. Their answer was the handicraftsman and genuine artistic finish in place of trade finish. William Morris defined real art as a person's expression of pleasure in labor, so the critique was about work as much as style.

Art Nouveau took shape in Brussels in the early 1890s: in one terrace house begun in 1892, an iron column in the stair hall sprouts iron bands at the top that curve into brackets, and swaying lines run through structure and ornament alike. Art Deco, from the mid-1920s, went the other way, with hard-edged geometry, vertical emphasis and stepped silhouettes. Ask whether the ornament flows or steps.

Modernism asked designers to start from purpose, structure and material instead of a precedent. A 1918 American critic put the complaint sharply: an engineer working in steel could not look to the past for help, while architects were taught that all the best songs had been sung. The International Style that followed dropped applied ornament altogether.

The Bauhaus began in Weimar in 1919, when an art school and an arts and crafts school were combined. Teachers of painting, sculpture and architecture worked beside teachers of the crafts, extending Arts and Crafts ideals, and an early stress on handicraft was later revised toward industrial production. Treat the name first as a school, which ran until 1933, and only second as a look.

The five points depend on one fact: a skeleton frame, not the walls, carries the building. Free-standing piers can then lift the house so space passes underneath, partitions can go anywhere, and long horizontal windows can run across a facade that holds nothing up. Each depends on that skeleton, which is why the points work as a system, not a menu.

Look for smooth plain walls, large windows, flat roofs and upper floors cantilevered past their supports, with no applied ornament. Underneath is a shift from mass to volume: raising a building on free-standing piers lets space pass beneath it, so it reads as an enclosed volume rather than a heavy block. Order comes from regular structure, not mirror symmetry.

An open plan needs a structure that does not depend on interior walls; then partitions become optional and space can flow around them, as in a 1922 country-house design whose space ran past free-standing internal walls. The usual cost is sound. GSA notes acoustics have troubled open offices since they arrived, and that higher partitions add only a little acoustic shielding.

A curtain wall hangs a skin of glass and metal on the frame; at Chicago's Federal Center, black-painted steel mullions frame bronze-tinted glass. The bill comes later, because daylight through glass drives heating and cooling loads and glare. One fully glazed Paris wall of the early 1930s was later cut up by added sun-breaks, and GSA has tested retrofits such as low-e window film.

Interwar modernists treated low-cost housing as a social service for architects' technical skill: one German estate of 1926 to 1928 was rows of concrete terrace houses with plain rendered walls and horizontal windows, and 1927 exhibition houses tested near-total prefabrication. Light and air answered slums such as an 1863 New York tenement where only six of 21 bedrooms got either except through the living room.

Organic architecture, in Wright's sense, fits a building into its site and into nature, with natural materials part of that fit, rather than imitating natural shapes. Taliesin, planned in 1911, wraps around a hilltop just below the crest, its changing levels and low roofs answering the slope. A useful test: could the design be moved to another site unchanged?

Wright's Prairie Houses of the 1900s took their name from a magazine design for a house in a prairie town. Low-pitched hip or gable roofs and long horizontal lines echoed the flat land most of them sat on, while the living space flowed around a central chimney core and out onto verandas and terraces. The horizontality answered the site: on a hilltop he built differently.

Wright called a later line of modest houses Usonian, beginning with an L-shaped house of 1937 near Madison, Wisconsin, with wooden sandwich walls and a flat wooden slab roof. The kitchen, his work-space, opened into the main living area and was lit by a clerestory, and the earlier ones were laid out on a square module. Many variants followed, some modest and some far larger.

Regional modernism keeps modern planning but takes materials and form from place. On the US West Coast in the 1930s and 1940s, a Bay Region manner used wooden construction, pitched roofs and looser plans in contrast to rigid steel-and-glass work, and in the early 1930s a leading European modernist built a rubble-walled house in Provence that accepted its landscape. Ask what the climate or local craft changed.

Continuity comes from letting a surface or a space run straight through the glass. In Wright's Prairie houses the living space flowed out onto covered verandas and open terraces, and at Chicago's Federal Center the plaza's paving grid continues into the ground-floor lobbies, so inside and outside read as one floor. Where the line stops at the glass, the room and the garden separate.

Beton brut leaves cast concrete as the finished surface, an industrial finish that some architects sought even in monumental work. To tell Brutalism from smoother modern work, look for the cues GSA's style guide lists: weighty massing, exposed concrete walls, broad wall surfaces and deeply recessed windows.

In twentieth-century concrete buildings, exposed structural elements were often treated as part of the design, inside as well as out. The idea is older than Brutalism: an early steel-framed skyscraper could already be praised because its steel frame was felt through the terra-cotta skin. Ask what is showing, and whether it is the real structure or an applied imitation of it.

The big civic buildings of the 1960s came with a building boom: GSA added over 7.7 million square feet of federal office space in 1961 and 1962 alone. A 1962 federal committee asked for architecture conveying the dignity, enterprise, vigor and stability of the government, but GSA's history notes the advice was left to officials' interpretation and was not widely applied outside Washington.

A module is a repeated unit that sets the size of every part. At Chicago's Federal Center a 28-foot grid, split into six modules of 4 feet 8 inches, runs from the granite plaza paving into the lobbies and up the towers, so paving, walls and facade all agree. Modular design pays off in coordination and growth; the risk is a grid that ignores the people using it.

Verdicts on 1960s federal concrete have swung. GSA's history calls Washington's housing department headquarters an example of the 1962 Guiding Principles; a 2020 executive order, revoked in 2021, said such buildings drew widespread criticism, and a 2025 order requires notice to the President before GSA approves a Brutalist design for a major federal building. Preservation law also makes agencies weigh historic buildings their projects affect.

Late-twentieth-century postmodernists treated buildings as signs that communicate, so a historical quotation on a facade was meant to be read. Philosophers now largely reject the strong version of that idea, that architecture is a language: a building can carry meaning, but it makes no assertions. Read a postmodern quotation as a gesture, not a sentence.

Postmodern theory learned from ordinary buildings, not just monuments. A 1972 study of Las Vegas, subtitled "The Forgotten Symbolism of Architectural Form," is one of the texts cited for that movement's program of reading buildings as communicating signs, and its title aims the lesson at a commercial city rather than a canon of masterpieces. The claim concerns meaning, not a taste for clutter.

A 2025 federal executive order defines deconstructivism as a style that emerged in the late 1980s featuring fragmentation, disorder, discontinuity, distortion, skewed geometry and the appearance of instability, and it discourages the style for new federal buildings. Read those features as the program: the instability is designed, not a failure of construction.

Parametric design defines a form by adjustable parameters, so software can generate variations and set every coordinate of a complex curved surface precisely enough to fabricate. One review separates that static use, which ends once the form is fixed, from a dynamic one in which performance data keep steering the design. The label parametricism itself has critics.

Commissioning a famous name to make a landmark has critics. In 1994 GSA created a Design Excellence Program; a 2025 executive order says it often selected designs by prominent architects with little regard for local input or regional taste, impressing the architectural elite more than the public. The debate turns on who a public building is meant to please.

When a building type travels, the conditions that shaped it may not travel with it. The nearly all-glass curtain wall of a New York tower of 1947 to 1950 was soon a kind of sheathing spreading rapidly to other countries, and one glazed Paris wall later needed sun-breaks. Philosophers add that some ethical questions show most clearly at global scale, such as unequal housing between rich and poor nations.

Density matters most for what it can support. EPA's guidance holds that about seven homes per acre are generally needed for basic fixed-route bus service, with higher thresholds for light rail. Compact, walkable areas near transit let people drive less, and compact neighborhoods also cover less land with paving.

In 1926 the Supreme Court upheld a zoning ordinance that kept apartment buildings out of single-family districts. The opinion called an apartment house in such a district often "a mere parasite" and worried that its height and bulk would block air and sun. The Court also said that if a classification is fairly debatable, the legislature's judgment controls.

Accessibility law sets minimums, such as an accessible route that must connect each story of a facility unless an exception applies. Universal design aims past that minimum: the accessible and inaccessible parts of a place become impossible to tell apart. It helps far more people than wheelchair users, from a parent with a stroller to someone with sore knees.

Calling a building "vernacular" is a judgment about its place in the art of architecture, a low-art category set beside the high-art buildings of trained designers. Philosophers note that we routinely judge the vernacular structures of other cultures as architecture without knowing their builders' intentions, which suggests the category depends on the viewer as much as the builder.

Under federal historic preservation review, consultation means seeking, discussing and considering other participants' views and, where feasible, seeking agreement. Consultation is not a vote, though: the final decision rests with the federal agency. So who is invited, and how early in planning, matters.

The envelope is the building's thermal barrier, and it helps set how much energy a comfortable interior costs. Its opaque parts alone, the walls, roofs and foundations, affect about 28 percent of building energy use. Leaks cluster at junctions: around windows and doors, between attics and the rooms below, and where siding or foundations meet walls.

Insulation slows heat flowing through a surface, and because walls have limited thickness, DOE research targets materials with much higher insulating value per inch. A thermal bridge is a local break or thinning in that layer, such as a slab edge, a window frame or a structural member passing through, where heat flows more readily and inside surfaces run cold enough to invite condensation.

Insulation and air sealing do different jobs. DOE compares insulation to a sweater and air sealing to a windbreaker: one slows heat, the other stops the wind. Air leaks also carry moisture that can warp wood and feed mold. Tightening a house raises the stakes for ventilation, since fuel-burning appliances still need air.

Passive solar design uses the building itself, not pumps or fans, to collect, store and spread the sun's heat. DOE's guidance puts collecting windows within 30 degrees of true south, unshaded from 9 a.m. to 3 p.m. in winter, with thermal mass behind a dark absorbing surface. Overhangs or trees then shade the same glass in summer.

Daylight saves energy only if it can replace electric light without driving people to the blinds. GSA's guidance warns that high daylight levels can bring glare and that sun on desks or in eyes must be avoided, using overhangs, exterior shading and coatings. Where it works, daylight harvesting at five federal sites averaged 27 percent lighting energy savings.

Natural ventilation runs on two forces. Warm air rises and is replaced by cooler air from below, the same stack effect that pulls drafts through a leaky attic. Openings on opposite sides catch wind for cross ventilation, which is why NPS guidance favors reopening historic transoms and keeping screen doors rather than sealing them.

Embodied carbon is the emissions from making, transporting, installing, maintaining and disposing of building materials; operational emissions come from running the building, whose operations use about 40 percent of U.S. energy. A whole-building life cycle assessment can compare refurbishing with demolishing and rebuilding, and GSA advisers urged weighing embodied carbon to favor reuse.

Rating systems score buildings on chosen criteria, and each has its own goal, stated or implicit, such as cutting greenhouse gases or improving indoor quality. Some award points for a life cycle assessment comparing design options. A certificate reports how a design scored against one scheme's goals; whether the building actually performs is a separate measurement.

HVAC systems deliver thermal comfort and fresh air, and they use about 39 percent of a facility's energy on average. Ducts carry conditioned air out from the air handler and back, and their size and number of turns set how hard the fans must work, like a wide straight straw versus a narrow bendy one. That is a plan decision, not only an equipment one.

Every fixture drains through a trap whose water seal keeps sewer air out, and a vent pipe from each trap admits air so a rush of water cannot siphon that seal away. An early-1900s plumbing text shows the vents of a laundry, kitchen sink, lavatory and bath rising floor by floor beside one stack, which is why stacking wet rooms saves pipe.

Lighting uses more than 30 percent of the electricity in U.S. commercial buildings, so it is a design decision as much as an equipment choice. It also couples to other systems: waste heat from fixtures can add cooling load, and window layout decides how much daylight can stand in for electric light. Coordinate them together, not in sequence.

Stairs are sized for evacuation, and their count matters as much as their width. In NIST's model of a 50-story office building, adding a stairwell beat widening existing ones for the same total width. Redundancy matters too: one stair can be lost to smoke, heat or fire hoses once firefighting begins, and a third stairwell offset the delay caused by firefighters climbing.

Federal workplace rules show what egress design controls. At least two exit routes are required, set as far apart as practical so one fire cannot block both; an exit is separated by one-hour fire-rated construction if it serves three stories or fewer and two-hour beyond; and each route must carry its floor's maximum occupant load without narrowing on the way out.

Model codes such as the International Building Code are published by the International Code Council, and FEMA tracks which places adopt them. A standard plays a different role: ASCE 7 sets minimum design loads and is referenced by the codes, so buildings within the code's scope must meet its wind provisions. FEMA's guidance on hazard provisions is written for owners, designers and code officials.

Noise control has three moves, often called absorb, block and cover: soft ceilings and panels absorb sound, rated walls and room zoning block it, and low background sound masks what remains. GSA guidance ties numbers to each: highly absorptive ceilings in open offices, and walls rated from STC 40 up to STC 53 depending on how private the room must be.

Each design phase narrows choices and sharpens the cost. In the National Park Service's design-build workflow, schematic design develops alternatives that meet the program and stay within available construction funding, each priced with a Class C estimate; the basis of design report that follows must support a more detailed Class B estimate.

Drawings and specifications are read as one contract. In the standard federal construction clause, anything shown on the drawings but not in the specifications, or the reverse, counts as if it were in both; where the two actually differ, the specifications govern. Discrepancies go to the contracting officer, and a contractor who adjusts on its own does so at its own risk.

Scale is chosen to carry information, not to fill a sheet. Federal measured-drawing guidelines call 1/4 inch to the foot useful for most building plans, elevations and sections, while site plans use engineering scales such as 1 inch to 20 or 40 feet. Very small buildings may go larger, and very large ones smaller, with details drawn separately.

Each delivery method moves risk differently. In design-bid-build, a finished design goes to bid, and chasing the lowest price can invite underestimated work, changes and delays. Design-build gives one team both design and construction; construction manager/general contractor brings a builder in during design, with price negotiated later. FHWA presents the alternatives as assigning each risk to whoever can best manage it.

Value engineering, in federal contracting terms, tries to remove anything that raises acquisition, operating or support costs without impairing essential functions or characteristics. That qualifier is the whole test. A cheaper substitute that drops something the design depends on, such as durability or a key quality of a space, is a cut rather than value engineering.

Every state and the District of Columbia licenses architects, typically after an architecture degree, supervised paid experience, and the Architect Registration Examination, with continuing education to keep the license. The stamp marks responsibility: interns produce documents, but a licensed architect edits, finalizes, signs and seals them.

The four federal treatments answer different questions. Preservation keeps a place's existing integrity and rules out uses needing major additions or demolition; rehabilitation keeps that character but allows major changes for a compatible new use; restoration returns a resource to one past period; reconstruction builds anew a resource that no longer exists.

Eligibility rests on significance plus integrity. The National Register asks whether a property is tied to important events or people, embodies a distinctive type, period, method or master's work, or can yield important information, and whether it still has integrity of location, design, materials and workmanship. Age alone does not qualify; places significant within 50 years ordinarily do not.

Repair what is deteriorated rather than replacing it, and design new work so that, if removed later, the historic building's essential form and integrity survive. Seismic guidance applies the same idea to structure: new reinforcement should be reversible where feasible, so better systems can replace it and historic material can still be repaired.

An addition should be differentiated from the historic building yet compatible with its massing, size, scale and features, and it should not destroy historic materials. Copying the old building too closely fails as surely as clashing with it. Before adding at all, check whether the new use fits in altered secondary interior spaces instead.

Adaptive reuse gives a building a new use while keeping what carries its significance, the treatment preservation guidance calls rehabilitation. Its strongest environmental case is avoided material: a life cycle assessment can show the benefit of refurbishing rather than demolishing and rebuilding, and GSA's advisers urged weighing embodied carbon to favor reusing existing buildings.

A treatment meant to help can harm historic material. Clean with the gentlest means possible, and avoid abrasive methods such as sandblasting or high-pressure water, which can damage masonry and its joints. When you repoint, match the historic mortar in strength, composition, color and texture: portland cement mortar on soft 19th-century brick has made some bricks spall. Repair rather than replace, and match any replacement to the old.

Major repairs, additions, a change of occupancy or local ordinances can trigger current code requirements, including seismic strengthening. The aim is to keep historic features in service, not replace them wholesale. Exposed reinforcement can be acceptable in plain buildings, while richly finished interiors usually call for hidden systems; work should be reversible where feasible.