Djenné Earthen Architecture

Djenné, in central Mali, is one of the best-known centres of Sudano-Sahelian earthen architecture. Its old town, inscribed by UNESCO in 1988 together with nearby archaeological sites as the Old Towns of Djenné, retains nearly 2,000 traditional earth houses, and its Great Mosque is the largest mud-brick building in the world.

Materials

Walls are built of sun-dried earth bricks (ferey) set in a mortar of sand and earth and coated with an earth plaster. The traditional wet-earth technique of the region is called banco. Roofs are made of timber, typically bundled palm sticks or beams, covered with layers of earth, producing a flat or very shallow roof.

The Great Mosque roof

The current mosque was rebuilt in 1906-1907 under the direction of Ismaila Traoré, head of the masons' guild. Its prayer hall has a mud-covered roof of rodier palm timber supported by nine interior walls with pointed arches. Small roof vents are capped with removable, inverted fired-clay bowls; when the caps are lifted, hot air escapes and the interior is ventilated. Ceramic half-pipes project from the roofline to throw rainwater clear of the walls.

Bundles of palm sticks called toron project about 60 cm (2 ft) from the walls. They are decorative but also act as permanent scaffolding.

Annual maintenance

Earth roofs and walls erode in the rainy season. Each year the community replasters the mosque: plaster is mixed in pits over several days and applied by men working from the toron and palm-wood ladders, directed by members of the masons' guild. The event has become a well-known festival. Houses are maintained the same way on a smaller scale.

Threats

UNESCO lists erosion and gullying from storms, uncontrolled urban growth and the introduction of cement, fired brick and metal doors and windows among the pressures on the town. Some decorative facade elements have disappeared as a result.

Wider significance

The Djenné roof shows the core logic of Sahelian earth building: thick earth for heat control, timber only where it is essential, waterspouts to protect walls, and a maintenance cycle carried out collectively.