Hausa Earth Vaults and Domes

Hausa builders of northern Nigeria and southern Niger developed a structurally ambitious earth-roofing tradition. Using only earth and short lengths of palm timber, they roofed rooms with flat roofs, arches, vaults and domes, some spanning more than 8 m (26 ft). The tradition is centred on old cities such as Kano, Zaria and Katsina.

Materials

• Azara: split timber from the deleb palm (Borassus). It is light, resists termites, and its fibrous surface bonds well with mud.
• Tubali: hand-formed conical or egg-shaped sun-dried mud bricks.
• Kasa: clay-rich earth used for mortar and plaster.
• Tabo: swamp mud, used for daubing and plaster.
• Burgi: gravelly clay used for rammed earth.

Flat roofs

For ordinary rooms, lengths of azara span between walls and are covered with mud. Because deleb palm timber is short, wider rooms needed a different approach.

Arches and vaults

The Hausa arch, built from cantilevered azara, gets round the short-timber problem. The first piece is set upright in the wall; further pieces are laid at progressively flatter angles, each overhanging the last and bound with cord. Masons work from both walls at once until the two halves meet, then add a reinforcing layer of timber over the joint. The whole frame is daubed with mud. In palaces, these arches support vaults spanning over 8 m (26 ft) and up to about 9 m (30 ft) high, and some arches carry an upper storey.

Domes

Domes (tulluwa) rest on intersecting half-arches and were built without centring, rising in layers from the top of round walls. Recorded examples include the dome at Kafin Madaki (1861), about 8.2 by 8.65 m (27 by 28 ft) and 6.75 m (22 ft) high, and the Soron Inglia hall in the Kano palace (1935), about 7.5 by 8.25 m (25 by 27 ft) and 9 m (30 ft) high. The architectural historian Labelle Prussin compared the structural logic of these domes to reinforced concrete.

Waterproofing and drainage

Dome surfaces were sealed with laso, a traditional render made from dye-pit residue, indigo liquor, ash and a sticky plant extract. It stays watertight for about five years before it must be renewed. Long projecting eaves (indororo) and spouts throw rainwater clear of the roof and walls, and decorative roof pinnacles (zankwaye) crown the parapets.

Builders

Building was organised through a masons' guild under a chief builder, the Sarkin Magina, with master builders (gwanaye) who trained apprentices for about ten years.

The Zaria Friday Mosque

Built in the late 1830s or early 1840s by the master builder Mallam Mikhaila, known as Babban Gwani, the Friday mosque at Zaria has a domed earth roof carried on massive piers and arches.

Change

Western construction forms were adopted quickly in the 20th century. Mosque roofs, traditionally of mud or thatch, are now often of metal sheet ("tin"). Some architects argue that modern materials used within traditional Hausa forms continue the masons' long habit of absorbing outside influences.