«The Nubian Vault: Earth roofs in the Sahel” The Nubian Vault: Earth roofs in the Sahel T. Granier1, A. Kaye1, J. Ravier1 and D. Sillou1 Association ...»
T. Granier, A. Kaye, J. Ravier, D. Sillou, “The Nubian Vault: Earth roofs in the Sahel”
The Nubian Vault: Earth roofs in the Sahel
T. Granier1, A. Kaye1, J. Ravier1 and D. Sillou1
Association la Voûte Nubienne (AVN), 9 rue des Arts, 34190 Ganges, France
Tel : +33 (0)4 67 81 21 05; Email : firstname.lastname@example.org
This paper describes a modern adaptation, simplification, and codification of the ancient
Nubian vault roof-building technique, developed and implemented on a significant scale by the Association la Voute Nubienne (AVN) in Burkina Faso during the last six years.
The AVN programme Earth roofs in the Sahel has undertaken the construction of over 200 vaults to date (mainly houses, but also including a church, a mosque, and several small hotels). This VN technique enables the construction of environmentally sound, well insulated, adobe / earth buildings with roofs which require neither timber nor metal sheeting – hence a valid and significant alternative to traditional flat-roof buildings of the Sahel, and to the more recent use of imported corrugated iron sheeting. The specific adaptations of the original technique include the use of a simple device to define the curvature of the vault, the strict specification of the depth of foundations and the thickness of gable and lateral walls, the use of embedded plastic sheeting in the roof to enhance impermeability to rain, and the speed at which apprentices can learn the technique on-the-job. Examples are given of the ways in which standard, modular, house designs can be adapted to specific clients’ needs, and of how the use of earth bricks can be combined with more modern materials such as concrete beams, and cement, where appropriate.
Full details of the AVN’s work, with many photos, and a video of construction methods and completed buildings, can be found at www.lavoutenubienne.org.
Keywords: Nubian vault, Earth construction, Timberless construction, Sahel, Sustainable building, Community involvement, Modular building, Apprenticeship
1. INTRODUCTION The technique of building unsupported vaulted roofs from sun-dried earth bricks (adobe) dates back at least 3,500 years, to the Nubian region of the Upper Nile – hence the term 'Nubian vault'. The contour of the vault approaches that of an inverted chain, or catenary curve, the ideal shape for a vault under compression . The oldest Nubian vault structure still standing, built of earth bricks, dates back to 1300 BC: the granary vaults of the Ramasseum, Old Gourna, Egypt . For centuries, this age-old method of building has persisted in many semi-desert and arid regions of the world, where timber is scarce: one example is Afghanistan . However, the technique largely remained unchanged, and confined to such regions, until the 1940's, when it was notably revived “Livingin Deserts: Is a sustainable urban design still possible in Arid and hot regions”. 1 Ghardaïa, Algeria, 9-12 December 2006.
T.Granier, A.Kaye, J.Ravier, D.Sillou, “The Nubian Vault: Earth roofs in the Sahel” by the Egyptian architect Hassan Fathy, with the building of a new village at Gourna, near Luxor . Architecturally, this village is a singular success; however, the families who were moved there soon abandoned it to return to their original homes. Furthermore, the buildings at Gourna, with their domes and large vaults and other complex adaptations, required levels of skill which demanded significant training for local builders to achieve the necessary competences.
A further example of a modern re-invention of the technique can be seen at Auroville, in India (Pondicherry), using dried adobe bricks to build a structure which is then fired in situ, after construction  – a complex technique requiring large amounts of timber for the firing, but resulting in strong weatherproof buildings.
A major drawback to the adoption of the Nubian vault technique outside regions where it is indigenous has been the time needed for builders to gain the necessary skills – traditional Nubian builders would spend years as apprentices before being able to work on their own, and the two modern adaptations cited above are not easily transposable without major training inputs.
Recently, however (since 1999), some builders in Burkina Faso, working with the the Franco-Burkinabe organisation, l'Association la Voute Nubienne (AVN), have managed to implement a simplified and codified version of the age-old technique in the Sahel. Apart from an earlier, smaller scale, initiative (in Niger, by the Development Workshop), this is the first time that the technique has started to be used on a significant scale in West Africa. During the last six years, the AVN and its associated builders in Burkina Faso have constructed over 200 vaults (mainly village homes, but also a Catholic church and a mosque). These environmentally sound, comfortable, and aesthetic buildings require neither imported sheet metal for the roofing, nor expensive and increasingly rare timber beams. Over 40 Burkinabe builders, as well as some from Mali and Togo, have been trained in the technique, and there are as many apprentices currently undergoing on-the-job training on building sites. The programme organised by the Association (Earth roofs in the Sahel) is developing rapidly year on year in response to demand from rural families, with many requests for help and technical advice coming from the countries of the Sahel.
This article reviews the AVN's programme, and the ways in which it can respond to the challenges of building in rural areas of the Sahel (desertification, lack of timber, high cost of imported building materials...) by developing vernacular skills and using readily available local materials (i.e. earth) for sustainable and ecologically sound housing. The unique factors that differentiate the Association's programme from other initiatives which on the surface, could appear similar, are described. They are to do with the simplicity of the VN (Voute Nubienne) technique, its standardisation, its modularity, and the fact that training of builders is carried out in the community, on-thejob, on actual VN sites (and not in formal training centres which, by definition, are removed from the local community).
2. THE VN CONCEPT
2.1 The challenge of building in the Sahel In sub-Saharan Africa, timber has always been used, traditionally, for roofing (flat beams and rafters made from rough timber and branches, supporting laths covered in earth; such roofs are supported by adobe / mud walls, incorporating load-bearing timber posts). Population growth in recent times, together with increasing “Living in Deserts: Is a sustainable urban design still possible in Arid and hot regions”. 2 Ghardaïa, Algeria, 9-12 December 2006.
T.Granier, A.Kaye, J.Ravier, D.Sillou, “The Nubian Vault: Earth roofs in the Sahel” desertification and regression of forested areas, means that these traditional building techniques are no longer feasible. People in rural areas now have to resort to buying sheet metal (corrugated iron) and sawn timber beams and rafters for roof-building.
These imported building materials, with their deplorable thermal, acoustic, and aesthetic properties, are often beyond the means of many people. They have to be paid for in cash, often a problem for families living outside any formal economic system.
Finding the necessary funds becomes a major drain on family resources, and does nothing to promote sustainable development.
In an experimental attempt to find a way of responding to these challenges, in the Spring of 1998, a Burkinabe builder (Seri Youlou), and a French builder (Thomas Granier), at the invitation of PIAMET, erected two prototype vaulted buildings in Boromo (central western Burkina Faso), entirely from earth bricks and earth mortar, without using any timber either for shuttering or in the structure of the buildings. The following year, with some technical advice from Acroterre (at the School of Architecture, Grenoble), and the help of local people wanting to get involved, two larger buildings were constructed, showing that the technique could in fact be popularised and adopted. Because of this promising start, in 2000, the AVN was formally established as a logistical support base for the Programme of Earth roofs in the Sahel, a programme that has since shown exponential growth from year to year.
2.2 Simplification and codification The principal reason why the AVN’s programme has developed over the last six years is due to the way in which the vault-building technique has been simplified and codified so as to enable rural builders and farmers, already familiar with earth brick fabrication and construction, to assimilate the technique within a relatively short period (i.e. during the traditional winter / spring building season, when agricultural work is minimal). The only raw material used is earth, for making both mortar, and mud bricks dried in the sun, timber shuttering is not needed to support the vault during construction, and existing traditional methods have been simplified and adapted to provide protection during the short but heavy rainy seasons of sub-Saharan Africa.
In more detail, a number of specific innovations distinguish the VN technique:
• A strict specification of building requirements for foundations, side walls, gable walls, openings, and, of course, the actual vaults, which, empirically, should not exceed an internal width of +- 3.2 metres (see Annex: VN Building Guidelines, for details).
“Living in Deserts: Is a sustainable urban design still possible in Arid and hot regions”. 3 Ghardaïa, Algeria, 9-12 December 2006.
T.Granier, A.Kaye, J.Ravier, D.Sillou, “The Nubian Vault: Earth roofs in the Sahel”
• The use of a stranded guide wire stretched between the two gable walls, along which runs a ring with a standard length of cord, to define a constant radius for the initial definition of the vault.
• The transformation of the upper section of the vault from a semi-circular to an ogival shape, empirically, by the addition of a finger’s length to the radius for each succeeding course of bricks over 70 degrees (thus approaching the ideal, Nubian, catenary curve).
• Use of specially made bricks for the vault, composed of high quality earth (e.g as made for granaries) mixed with straw, with optimal dimensions of +- 24 cm long X 12 cm wide X 4.5 cm thick, light enough to stick to the fresh mortar near the top of the vault.
• The inclination of the brick rows of the vault to a lower angle than vertical (+/-60°), to make the already built rows bear a part of the load of the rows actually being built.
• Use of oil drums as temporary supports for forming window and door arches.
• The use of plastic sheeting over the roof, covered by a final waterproof rendering (at least 6 cm deep) to protect it from solar degradation, and to reduce the annual maintenance load for the roof.
“Living in Deserts: Is a sustainable urban design still possible in Arid and hot regions”. 4 Ghardaïa, Algeria, 9-12 December 2006.
T.Granier, A.Kaye, J.Ravier, D.Sillou, “The Nubian Vault: Earth roofs in the Sahel”
2.3 Modularity and customisation The AVN has prepared for builders and clients five standard house plans, based on different permutations and combinations of one or more basic vaulted units; these range from a two-bedroom house to a simple ‘bachelor pad’.
The plan for a house of 52 sq metres of living space (2 bedrooms, living room, shower, and kitchen) is shown in Figure 3. The labour required for such a house is around 26 man-days of two builders, and the same again for two apprentices and two labourers; materials needed are 30 barrows of laterite rocks, 4300 large bricks (c. 38cm X 18 cm X 18 cm), 130 barrows of ordinary earth for the walls, 70 barrows of good quality earth for the vault bricks and mortar, and 150 barrels of water. An example of a completed house of this type is shown in Figure 4. Examples of the other basic plans and associated labour and materials can be found on the AVN website .
However, the fact that these standard, modular, designs exist does not imply that clients and builders have not modified, adapted, and improved the basic VN methods and structures. For example, many clients have asked to have the vaulted roof “Living in Deserts: Is a sustainable urban design still possible in Arid and hot regions”. 5 Ghardaïa, Algeria, 9-12 December 2006.
T.Granier, A.Kaye, J.Ravier, D.Sillou, “The Nubian Vault: Earth roofs in the Sahel” transformed into a traditional Sahelian flat roof-terrace: this can easily be done by raising the side walls and filling in the sides of the vault with earth, bricks, and earth mortar. This also strengthens the vault and provides better thermal insulation. During the last building season (2005/2006), two-storey houses have been built (see Figure 5), with either external or internal stairs: the second storey vault being built on top of the flat roof-terrace formed by the ground floor vaults.
Figure 5 Two-storey house at Boromo, Burkina Faso
Many other examples have already arisen of adaptations and modifications of the VN technique, both by clients and builders, ranging from the very simple to the most sophisticated. Initial plans and dimensions have been changed, and improvements made to the layout and finishes, depending on clients’ aspirations and resources. Such innovations enrich the scope of the VN principle, provided the basic technical principles of construction of the vaults are respected.
Examples of popular modifications of interiors include integrating an electrical supply into the masonry, cement rendering of the lower half of internal walls, and interior showers with cement floors and tiling.
“Living in Deserts: Is a sustainable urban design still possible in Arid and hot regions”. 6 Ghardaïa, Algeria, 9-12 December 2006.