PART FIVE: TECHNOLOGY AND SOCIETY 862 authorities believe it stemmed from the boat-building traditions of Scandinavia, others that it has affinities with the pointed arch of Gothic design (see p. 874). More probably the form evolved from practical needs and limitation of knowledge as did the similarly-shaped early corbelled stone structures of areas as far apart as Mycenae in Greece or the Celtic oratories of western Ireland. In early cruck construction the basic timbers, the crucks, were massive whole or split tree trunks, the lower edges of which were fixed into the ground in pairs at intervals in the long sides of a rectangular building—the interval was generally some 3.5–5m (12–16ft)—and the narrower tops were then bent over to be fastened together in the centre so forming an apex to the roof. A long horizontal timber, the ridge piece, was extended along this whole roof, the crucks being affixed to it. Parallel to the ridge piece were other slenderer poles and these were crossed at right angles by more timbers. The interstices were filled with branches and mud and covered on the exterior by moss, thatch or turf. The great drawback to the single-storeyed cruck building was its lack of headroom, as it had no vertical walls, so the design was further developed into two-storeyed buildings as the crucks were taken up higher. The next stage was to extend horizontal tie beams across the interior and beyond the crucks to attach to horizontal timbers, at right angles to the tie beams, which would carry the roof and act as the summit of the now vertical walls. Gradually cruck structures became more advanced and practical. The lower ends of the crucks were set into low stone walls or timber sills instead of directly into the ground. The crucks were shaped before use, a pair forming a symmetrical arch. More complex roof designs followed (see pp. 865–6). Timber-framing In regions of northern Europe, especially where hardwoods were available in quantity, as in England, a more sophisticated method was evolved in which split timbers were attached together to form basic framework for a building, which would have vertical walls and a gabled roof (see Figure 18.1 for an example of this type of structure). The panel spaces between such framing were then filled with other materials—wattle and daub, laths and plaster or brickwork. This type of construction is also known as half-timbering, because the tree trunks were halved or cleft, not complete logs. The trees were stripped of their bark and soaked for a year or more in water to season the wood before use. Many designs of timber-framed structures were developed over the centuries. In England there were two fundamental types: the box-frame and the post and truss. The first of these was built with horizontal and vertical timbers crossing at right angles and fastened together to make box shapes. In the latter designs, vertical posts supported a truss, that is, a group of strong timbers formed into a framework within the triangle of the roof gable. BUILDING AND ARCHITECTURE 863 Figure 18.1: Timber-framed inn. The Feathers Hotel, Ludlow, Shropshire, late sixteenth century. Photograph Doreen Yarwood. PART FIVE: TECHNOLOGY AND SOCIETY 864 The simplest type of truss is a triangle formed from three beams and, in building, grew out of the use of the gabled roof. The Greeks of Hellenistic times invented the truss, finding the triangle to be a rigid form. The earliest surviving description of a truss is in one of the volumes of De Architectura by Vitruvius, the Roman architect and engineer of the first century BC. In timberframe construction there is a horizontal timber (a tie beam) and two sloping timbers fastened together at the apex. The weight of any roof creates a thrust which attempts to push the upper part of the walls outwards which is counteracted by the horizontal beam tying the sloping timbers together. In later centuries the theory of this single rigid triangular truss was elaborated, as in the classical trussed bridge design in which combinations of triangles were used. Later still, in the nineteenth century, with the availability of cheap, strong iron and steel, large, complex trussed roofs were constructed to cover railway sheds and stations (see p. 893). In modern times, vast and complicated trusses have been created to enclose great auditoriums (see p. 879). Whatever the design of timber-framing there was a similarity of basic parts and methods of construction. In order to exclude the damp, the framework was usually erected upon a low wall of more impermeable building material, such as stone or brick. Upon this footing were laid horizontally baulks of timber called sills or plates. Strong vertical posts (the studs) were then mortised into this sill and their upper ends tenoned into another horizontal plate. In most types of timber-framed buildings the upper storeys projected over the ones below. This overhang is called a jetty. When a building was jettied on all sides, additional support was provided for the structure by internal cross members known as dragon beams which extended diagonally from the centre to the corners of the upper floors. Jettying had several purposes. Of importance on limited town sites, it gave a greater area of floor space to the rooms of the upper storeys. The lower storeys were protected by those above from rain and snow at a time when there were no down pipes or gutters. Jettying also gave a more balanced stability to the upper floors themselves. Oak timber-framed buildings did not require preservative sealing. The black and white effect which many surviving structures show is due to a nineteenthcentury custom of painting them with a coal derivative tar with the plaster panels whitened for contrast. Many owners are now stripping their timber-work back to its original silvery hue. Timber-framed buildings were largely prefabricated and they may, without too much difficulty, be taken down and re-erected as has been done in a number of instances, for example, on open-air museum sites. Originally the larger timbers were cut and shaped on site but smaller ones were made in a carpenter’s workshop and brought to the building. The infilling was put in floor by floor, so completing the structure as the building was erected. A form of decoration known as pargeting, using abstract patterns or representational figures, was sometimes impressed into the wet plaster between the timbering. BUILDING AND ARCHITECTURE 865 Stave churches A different type of timber construction may be seen in the stave (mast) churches of Norway. In these the roof was not supported on the walls; each part of the structure was self-supporting. The building was based upon a skeleton framework of vertical poles (the masts) which were slender tree trunks. The lower ends of these were sunk into horizontal sills and the upper ends supported the roof. There were cross beams near the top of the poles. The walls of such churches are stave screens, self-contained wooden panels—rather like modern woven fence units— which rested upon the timber sills and were attached to the poles but did not take any weight or thrust. In advanced designs of churches of this type, there is an inner ring of ‘masts’, so giving a nave and aisles to the interior. Stave church design is based upon timber shipbuilding in which each section is a self-sufficient unit. The interiors are tall and dark, bearing a resemblance to inverted timber ships. They were constructed from about the eleventh century until the Reformation, and during the nineteenth century about 500 churches were extant. Their number is now greatly depleted and most survivors have been extensively restored. A superb example is St Andrew’s Church of Borgund near Laerdal; it was built c., 1150 and is about 15m (50ft) in height, erected in six storeys. Another example near by is the church of the tiny community at Urnes. Log construction From the sixteenth century onwards timber building in Scandinavia followed the more usual pattern of that in eastern Europe which was to build with whole logs or logs split only down the centre, constructing with the curved side of the log on the exterior of the building. Many examples of structures of all types, erected over hundreds of years until the early twentieth century, may be seen in the open-air museums where they have been re-erected to save them from total loss. Of particular interest is the Norsk Folke museum at Bygdøy Park near Oslo, the Aarhus Museum (Den Gamle By) in Denmark and the Village Museum in Bucharest. The English equivalent, displaying timber-framed building, is the Weald and Downland Museum at Singleton near Chichester. The timber-trussed roof This is an open interior roof system composed of a rigid construction of timbers (the truss) which were pinned and tenoned together to provide a stable combination which could resist all thrusts. Such roofs, constructed in Europe chiefly between the eleventh and sixteenth centuries, represent the timber equivalent of the stone vault (see pp. 874–6). PART FIVE: TECHNOLOGY AND SOCIETY 866 The earliest designs were based on cruck construction, but gradually a more sophisticated system was evolved empirically which would provide better headroom and not obstruct the interior visibility. The medieval roof was generally gabled at each end and, at least in northern Europe, was fairly steeply pitched. A long baulk of timber extended along each side of the building on top of the walls: this was the wall plate. Another such baulk was the ridge pole or ridge piece, extending along the roof apex. Between these two were other beams running parallel to them, fixed at intervals down the slope of the roof pitch: these were purlins. Crossing these beams at right angles were the rafters which extended from wall plate to ridge piece. At regular intervals were heavier rafters, called principal rafters; in between were the thinner common rafters (see Figure 18.2). The simplest and earliest form of timber-trussed roof was the tie beam design. These tie beams were heavy baulks of timber spanning the interior at intervals and pinned or tenoned into the wall plates in order to offset the outward thrust of the roof upon the walls. Upon the beams were generally set one or two vertical posts extending from them up to the ridge piece. If there is one central post, it is called a king post, if two, they are queen posts. Horizontal beams set higher up the roof are called collar beams. Connecting timbers were incorporated to make the structure rigid. If straight they are called struts, if curved, braces. A coupled roof is one constructed without tie or collar beams but only struts or braces. It gives better internal visibility but is less strong. Vertical posts extending from collar beam to the ridge piece are called crown posts. In the late fourteenth century came the final and more complex design: the hammerbeam roof. Hammer beams are like truncated tie beams. Extending at wall plate level, they are supported from stone corbels embedded in the walls by arch-braced wall posts. These shorter hammer beams gave better visibility than the continuous tie beams. Vertical posts (hammer posts) stand upon or are tenoned into the ends of the hammer beams and are attached to the collar beams above where they join the purlins. Hammerbeam roofs are richly decorated by carving, gilding and painting: many, especially the later examples, for instance at Hampton Court Palace, are particularly ornate. The finest hammerbeam roof is Hugh Herland’s earlier structure of 1394 covering the interior of Westminster Hall in the Palace of Westminster in London. BRICK AND TILE Brickwork Brick has been used as a building material for thousands of years. It has many useful qualities: it is cheap and easy to make, the raw material is available almost anywhere, it can be manufactured in different sizes, colours, qualities and tex tures and it is durable, withstands the weather and is a good insulating BUILDING AND ARCHITECTURE 867 material. It is also convenient to use in conjunction with other materials, partly as bonding courses for added strength (as in Roman walling) and partly as a colour contrast, a custom practised by many architects, for example, Sir Christopher Wren, who used Portland stone as dressings for his brick buildings. Figure 18.2: Timber-trussed roof with braced collar beams. Manor house, Solar, c. 1475–85. Drawing by Doreen Yarwood. PART FIVE: TECHNOLOGY AND SOCIETY 868 Early bricks, in areas of the world where the climate was sunny, were sundried. Harder bricks were obtained by being exposed to heat from fire. Such burnt bricks were being made in the Near East by 3000 BC. Later references show such use in many parts of the world. The fifth century BC Greek historian Herodotus tells us that such bricks were made to build the city walls of Babylon. The Chinese used them in the third century BC to construct parts of the Great Wall. The Romans (as did the Etruscans before them) made extensive use of brick in all forms of construction. Such bricks were sun-dried until the first century BC, after which kiln-burnt bricks became more general. It was the proud boast of the first Roman emperor, Augustus, that he found Romé a city of bricks and left it a city of marble, but this only referred to the facing of the buildings, which were still largely of brick construction underneath. Roman builders used brick for arched openings, as bonding courses in walling, for relieving arches in vaults (for example the Pantheon in Rome) and for the colossal spans of the great basilicas and baths where they utilized brick compartments in vaulting in conjunction with concrete. This wide use of brickwork was extended further in the eastern area of Roman influence which later became the Byzantine Empire. Roman building bricks were hard, large and thin, resembling large tiles, and were laid with thick courses of mortar between. Floor bricks were were also rectangular but smaller. Hypocaust pier bricks were square. After the collapse of the western part of the Roman Empire in the fifth century AD, brickmaking died out in much of western Europe, especially in Britain where it was not revived until the thirteenth century. Throughout the Middle Ages, however, brick was a vitally important material along the coastal regions of the North and Baltic Seas and bricks were being made from the early Middle Ages along this coastal belt which extended for 1200 miles from Bruges in Belgium to Novgorod in the USSR, the area made wealthy under the administration of the Hanseatic League. Because it lacked other permanent building materials brick was developed as a constructional and stylistic material for all types of building from cathedrals and castles to guild halls and manor houses. Brick is not an easy material to make into decorative forms, but a simplified version of both Gothic and the later classical architecture of Europe was created over the centuries by skilled craftsmen of the region and resulted in a remarkable unity of style over so many countries in such a large area. Bonding In early brickwork, bricks were laid irregularly and, in walling, were often mixed with flint and/or stone. As the work became more skilled bricks were laid in a form of bonding, a uniform arrangement which ensures strength and BUILDING AND ARCHITECTURE 869 is also decorative. Many different types of bonding have been developed over the centuries. These vary from area to area but it has also been found that some bonds are stronger than others and these are often more costly, so a bond is chosen for a specific commission according to the quality and appearance required whether it be an important building or a garden wall. In England the most usual bond to be employed in medieval brickwork was that termed English bond, which consists of alternate courses of headers and stretchers. A header is a brick laid so that only its end appears on the wall face; a stretcher is laid lengthwise to the face. This type of bond was in general use in Tudor structures but, by the 1630s and 1640s, when brick building in England was becoming much more common, partly due to the depletion of timber stocks, Flemish bond gradually replaced it in popularity. This is laid with alternate stretchers and headers on each course; an early example is Kew Palace, built 1631. The great age of English brick building was the century beginning in 1660 when high quality bricks were manufactured from a variety of clays. Limited technical advances were made and the cost of brickmaking decreased, leading to a growth of brick building. Unfortunately in the later eighteenth century, this situation attracted the attention of government: a brick tax was imposed in 1784 and soon was twice increased, resulting in a serious curtailment of brick building of smaller structures in rural areas. The brick tax was repealed in 1850. Contemporaneously the building needs following the tremendous population explosion and those of urbanization stemming from the Industrial Revolution led to an immense acceleration in brickmaking. Partly this boom was to serve the housing building industry but it was also for the construction of railway viaducts, tunnels, cuttings and stations, as well as factories and warehouses. Technical advances and improvements in brickmaking rendered the material the cheapest and the most ready to hand. Bricks were made for all purposes in different qualities by different processes. A wide range of colours was available and Victorian architects readily adopted the fashion for polychromy in their designs. Brickmaking Three chief stages of production are involved in the making of bricks from clay by heating or burning them. This has been so since the earliest bricks were made though, with the passage of time, the methods for carrying out the processes have become more complex and mechanized. The raw material has to be dug out of the ground, it then needs to be prepared and moulded into shape and, afterwards, burnt. After the clay has been dug, it has to be puddled. This is a preparation process which includes removing pebbles and extraneous matter from the clay, PART FIVE: TECHNOLOGY AND SOCIETY 870 then mixing and squeezing it with the addition of water and sand to give an even consistency. Often more than one clay is used in the mix so that the properties of one will counteract or improve the properties of others. Before the seventeenth century puddling was done by men treading the substance barefoot. After this the pug-mill gradually replaced the human labour. The mill was cylindrical; it contained a central shaft with blades attached which acted in the same manner as a butter churn. Early mills were powered by a horse or donkey on a treadmill (see Chapter 4). Later the pug-mill contained rotating wheels and, according to date, was powered by water, steam or electricity. The early way to mould the bricks into the shape required was by human hands. During the Middle Ages moulds were used and later these were made with detachable base so comprising a stock mould and stock board. Clamps were constructed in early times for brick burning. The clamp consisted of stacked bricks intermingled with brushwood which was the fuel. The clamp was lit from the exterior and allowed to burn itself out. This method caused bricks to be unevenly fired, the ones on the interior of the clamp being burnt more than those on the exterior and so, having lost more water, they were smaller and darker in colour. It was this which gave to fifteenth- and sixteenth-century brickwork an interesting variety of shape and tone. On a site with a suitable clay sub-soil, the whole brickmaking process might at this time be carried out where the building was to be constructed. Gradually the kiln system superseded the clamps and, after about 1700, coal and coke replaced wood as fuel. At this time advances in brickmaking slowly took place but it was the midnineteenth century before these resulted in mass-production systems. Then many hand processes became mechanized, also delay in drying bricks before firing was eliminated by mechanical drying. The introduction of the Hoffman Kiln of 1858 was a great advance as its multi-chamber system enabled the firing process to operate continuously with brick stacks at different stages of firing or cooling instead of waiting for a fortnight for each setting of bricks to dry as before. The development of the Fletton process in the 1890s was a further great advance. Fletton is an area near Peterborough in Cambridgeshire, where a certain shale-clay is found in quantity. This material has a low water content which makes it suitable to be pressed into a brick mould without previous drying. Finally, brickmaking machinery replaced remaining hand processes for making bricks about 1885, vastly increasing the speed at which bricks could be turned out. Tiles Also fired in a kiln, tiles are less porous, harder and smoother than bricks. They are traditionally used for roofing and also for wall and floor covering, BUILDING AND ARCHITECTURE 871 where they might be decorated and glazed. In England, in the later seventeenth century, the craft of tile-hanging was developed. Also known as weather-tiling because of its use as protection from rain and snow, it is ornamental, too, and varied designs were adopted. The tiles were hung on wood battens plugged into the walls or were pegged or nailed into mortar courses. In general, tile-hanging was practised more in the south of the country and slate-hanging in the north. Another use for tiles was found in the second half of the eighteenth century; these were called brick tiles, alternatively, mathematical or weather tiles. These were generally made to the same linear dimensions as bricks and their purpose was to be applied to walls as a tiled skin to cover the original material of the wall behind which might be timber and plaster. An older, simpler building might thus acquire the appearance of a more fashionable brick one. These tiles were employed by many of the fashionable architects of the day and especially in the south-east of England; the Royal Crescent on Brighton sea-front (c. 1800) is a notable example where black glazed tiles have been used. Terracotta and Coade stone Terracotta is also a fired earthenware material which is harder and less porous than brick. It is used chiefly for decoration on buildings where it is moulded into ornamental or sculptural forms. Its use was introduced into England in the early sixteenth century by Italian craftsmen as can be seen, for example, in the roundels on the gateways of Hampton Court Palace by Giovanni da Maiano. Architects of the nineteenth-century Gothic Revival utilized terracotta extensively as a decorative medium. A well-known instance of this is Alfred Waterhouse’s Natural History Museum in London (1873–9), where the architect faced the façade in two shades of the material—buff and grey—and decorated it with a wealth of animal and plant sculptures. The mix for terracotta includes grog, that is, previously fired earthenware ground to a powder and this was also the basis for Coade stone, an extremely hard and durable material which was employed as an artificial stone by most of the leading architects of the day, including Robert Adam, Sir William Chambers, John Nash and Sir John Soane. The manufactory of Coade stone was established by Mr and Mrs Coade in 1769 in Lambeth and it was run by their daughter Eleanor. The formula for the material was kept very secret but modern analysis has shown it to be a combination of china clay, grog from pulverized stoneware and various fluxes. It was a particulary stable, smooth substance eminently suited to making larger-thanlife-size statuary and ornament and it has, in many instances, endured city atmospheric pollution better than actual stone, This may be seen, among other famous buildings, at the Royal Naval College in Greenwich, . city walls of Babylon. The Chinese used them in the third century BC to construct parts of the Great Wall. The Romans (as did the Etruscans before them) made extensive use of brick in all forms of construction beams and, in building, grew out of the use of the gabled roof. The Greeks of Hellenistic times invented the truss, finding the triangle to be a rigid form. The earliest surviving description of. slender tree trunks. The lower ends of these were sunk into horizontal sills and the upper ends supported the roof. There were cross beams near the top of the poles. The walls of such churches are