Traditional building construction

The buildings use local earth/straw brick covered externally with earth/straw plaster as their universal method of construction.

Shibam. Workmen repairing a plaster wall high above the street; the rope cradle is fixed to the parapet at the top of the house.

Sometimes timber beams are inserted in the walls for reinforcement, but they and the windows and doors are vulnerable to attack by insects if the wood is not properly selected. Only at the top and bottom of the building is waterproof lime plaster used.

The earth. Tests have shown that the material of the bricks and mortar is of excellent quality, unusually high in its content of binding agent, clay (about 10 per cent). This is because the earth was traditionally gathered from around the roots of the date palms, a practice which the government has now prohibited. The builders are therefore using earth gathered from the non- agricultural parts of the wadi, where there is less clay and humus. It is hoped that further study will permit the discovery of natural clay deposits with which to strengthen the bricks and mortar again. In the meantime, an inferior practice of reusing fallen earth from old buildings is being discouraged, since it has generally lost its clay and is full of salts.

The wood.The principal structural difficulty in building the Shibam houses was the problem of finding timber long enough. There is some evidence that in ancient times teak imported from India was used, at least in some of the buildings. In recent decades, the importation of teak, and also of wood from Africa, has revived. But for much of its long history Shibam had available only two woods for building, elb or sidr, known as himr when it gets old and hard, and ithl or tamarisk. Neither species grows to any great height, so the beams of the rooms tended to be limited to about 3.5 m. Longer beams, to cross large rooms on columns, were sometimes jointed longitudinally, or 'ariata wood was used, obtained from the few areas where this taller species grew (although long beams were extremely difficult to transport over the rough terrain on camel-back so beams of great length were rarely employed). There were ancient restrictions against cutting trees in many areas of the wadi, and the government today is enforcing the protection of the indigenous flora, so that elb wood can now be obtained only with extreme difficulty and at great expense. Traditionally, this wood was also used for all the doors, window screens, shutters and cupboards. In the most exposed situation it lasted fifty or sixty years. But internally it was regarded as indestructible. If the trees were felled in winter, the preferred season, there was little sap rising in the wood and it was accepted as insect-proof. Termites were rare in Shibam, and since the main beams were mostly of this wood, they were almost never replaced. (The only exceptions were splitting due to settlement, or overloading due to building higher storeys carelessly over the beams.) The small beams, which spanned crosswise, approximately twelve in each bay, were sometimes attacked or became rotten. This would happen if ithl had been used for them rather than elb. If four or five were rotten in a single section they were replaced, or perhaps the whole floor construction was redone and the beams replaced.

If exposed to the weather, ithl wood lasted only about fifteen years. It was consequently a much cheaper wood, used only in poor houses.

The foundations: The site was cleared first and trenches for the walls dug down until a hard layer was reached, usually about 1.6 r below ground level.

Shibam. The frames for making two of the five sixes of mud-bricks used in the construction of the tower houses.( Each of the frames is a mould for two bricks.)

The trench to receive the foundations was one and a half times to twice the dimension intended for the wall thickness at ground level. The bottom of the trench was first covered with a layer of animal droppings 3 cm deep. On top of this, rock salt was laid to a depth of 8 cm, which made the ground very strong. Then wooden (elb) logs 10-20 cm in diameter were laid parallel to the length of the wall, and of the same width as the trench. Small stones were used to fill the interstices between the logs and to bring the foundation footing up to a uniform level. Then a layer of ramad (lime/ash mortar) was laid, on to which a first course of rubble stones was placed. Successive courses of stone brought the foundation wall up to above ground level. In the best-quality work all the stones were laid in ramad. Only in work of inferior quality was the core of the mortar work of earth, with merely the faces on the outside of the foundation wall plastered with ramad or lime mortar. The width of the stone foundation wall tapered inward slowly until ~t reached the intended width of the mud-brick wall. But the stonework continued up above ground 50 cm to I m before the first brick course was laid.

The foundations described above were of the very best types for the highest houses. Lower and poorer houses might omit the ramad mortar and use only clay. And in the poorest constructions there were no stone foundations at all, but unburnt clay bricks were used instead, rising from the elb logs.

The building unit of measurement. The unit employed by the builders was the dhira, which may have varied here, as it did elsewhere in Islam. But in the last forty years it seems to have approximated 45.8 cm. All parts of the building were referred to by the builders as fractions or multiples of the dhira.

The staircase pier. The strongest part of any house was the central pier of the staircase, the arus al-bayt, often built throughout most of its height of rubble stonework even when all the remainder of the structure was of mud-brick. It was usually at least approximately 3± x 3 dhira (1.5 x 1.25 m) in plan. In the best work the stone pier was reputedly set in lime/ash, i.e. ramad, mortar. But the majority of the staircase piers were probably of stone laid in earth mortar, and many changed to mud-brick at quite a low level.

The mud-bricks. The bricks were made from sandy soil containing some clay, which was mixed with fine chaff or chopped straw.

Shibam. Plasters applying a new waterproof dado in ramad at the base of a tall house.

Enough water was added to produce a malleable mud, and the bricks were cast immediately, without any puddling process, using a wooden frame of the type illustrated in Plate 58. Five sizes of brick were normally used in a house. At the ground-floor level, the dimensions of the bricks were 1(1/10) X (7/10) dhira (50.5 x 32.75 cm), the second-size bricks were (9/10) x (2/3) dhira (42.5 x 30.5 cm) and so on to the fifth-size bricks which measured 0.55 x 0.53 dhira (25.5 x 23 cm).

The thickness of the wall. This was correspondingly: on the first or ground floor, 1(7/8)) dhira (86 cm); on the second, 1(1/2) dhira (69 cm); on the third, 1(1/4) dhira (57 cm); on the fourth, 1 dhira (46 cm); on the fifth, (3/4) dhira (34.5 cm); on the sixth, (5/8) dhira (28.5 cm); and on the seventh, (1/2) dhira e (23 cm). These dimensions would naturally vary from builder to builder and from house to house. The resulting slope on the wall occurred on the outside face, the inside being vertical.

Plaster. Mortar and plaster were of two types: that made with earth and that of lime.

The earth plasters and mortars were made in very much the same way as the bricks, but with a greater admixture of chaff or chopped straw in the external plaster, and especially careful selection of the earth to ensure that it had a good admixture of clay.

The lime plaster, or ramad, used externally, and as a mortar in best foundations and stair piers, had a large quantity of ground wood charcoal as a setting agent, as well as coarse and fine sand.

Ramad plaster was laid on a subcoat of earth/straw plaster, and the mixture was beaten very laboriously into a fine powder before being mixed with water. After being applied, it was finished with whitewash.

Internally, the lime skim coat was used without ash; it was laid over the mud/straw subcoat and burnished with a smooth flint until it was polished and reflective.

A more sophisticated version of this internal polished plaster used egg-white as a binding agent, which was said to impart a greater sheen. Householders used to boast of the large number of eggs that had been used in the finishing of the house. The lime was burnt in small mud-brick kilns, using dung as a fuel, either in some open place in the city or on the outskirts. When the lime was sufficiently baked, it was mixed with water in a trench, and from ten to twenty men then beat it with heavy sticks to break up all the lumps, standing on opposite sides and smacking it alternately, chanting as they worked.

Elaborate rituals were observed in the building of a house. For instance, a goat or a sheep was slaughtered as soon as the stonework of the foundation was finished to full height, and the blood was spilt over one or more corners of the building. A devout man usually attended the ceremony and the carcass of the slaughtered animal was afterwards divided, most of it going to the stonemason and the other workmen, and a fifth to the owner of the house.

A similar sacrifice used reputedly to be made at the beginning of the whole building operation, after the trenches had been excavated and the animal dung and salt laid in place.

The owners provided several feasts for the builders at various stages in the erection of the lintels and floor beams, and on the completion of the building.

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