Housing in African Rural Contexts: The Nubian Vault. Opportunities for the Economic Market in the Rural Savannah Environments

Abstract

It is well known that the level of human development of most parts of West African nations is among the weakest of the whole planet. The housing sector, which responds to a primordial necessity, constitutes one of the greatest potential for exploiting resources that are still available and unexplored. The debate on housing issues is today mainly focused on the phenomenon of urbanization, where large megalopoles are fed with uninterrupted streams of populations from the countryside. It follows that most researches on the conditions of habitat ignore the state of rural housing where valuable case studies are virtually absent. An oblivion of research that hides an area of architectural intervention in which there is still a lot be done. The rural context is a decisive factor for a challenge to which the debate on architecture is also called to respond.

Appendix: The Nubian Vault. Criteria—By the Nubian Vault Association

Source courteously by http://www.lavoutenubienne.org/.

1.1 A Roof: The Nubian Vault Technique

The Nubian Vault technique is based on an age-old method of timberless vault construction, originating in Upper Egypt a region at the same latitude as the western African territories on which this article is focused.

The Nubian Vault construction method is:

Ecologically sustainable:

using neither corrugated iron roofing sheets, which are expensive and difficult to recycle, nor timber beams, rafters, or supports.

Carbon neutral:

none of the building materials need to be manufactured or transported long distances, nor do any trees need to be cut down.

Economically viable:

locally available raw materials (earth, rocks, and water) are used, thus favoring local economic circuits and self-sufficiency.

Comfortable:

due to the excellent thermal and acoustic insulation properties of earth construction.

Durable:

NV buildings have a far longer lifetime than those with corrugated iron and timber roofs, and maintenance is simple.

Modular:

it can be used for a wide range of buildings (houses and public infrastructures) which are easily extendable.

Appropriate:

AVN’s simplified and standardized version of the technique has been adapted to the climatic conditions and traditional know-how of the Sahel region, making it easy to learn on-the-job.

1.2 A Skill: NV Masons

The majority of trained NV masons collaborate with AVN, exchanging ideas and information about the market, clients’ needs, and potential apprentices, both informally, and at formal congresses arranged by AVN each year. Some of them go further, getting involved as extension agents promoting the VN technique, for which AVN then provides compensation. Apprentices are chosen from the local population: The selection is made by the local community in collaboration with experienced NV masons. Apprentices progress from laboring work, to making bricks for the vault, to observing and assisting experienced masons in the skilled work of vault construction. Depending on the level of commitment and the starting point of each apprentice, it can take one or two construction seasons of on-site apprenticeship before an apprentice began able to build a vault.

There are five, progressive, classes of NV apprentices and masons, all of whom are trained on actual NV building sites:

C1:

apprentice

C2:

advanced apprentice

C3:

mason, able to build a vault

C4:

foreman, able to supervise a construction site

C5:

builder-entrepreneur, able to negotiate with clients and supervise several sites

The rate of recruitment and training of apprentices is one of the main factors affecting the growth of the Program. At the end of their apprenticeship, and with the support of AVN, newly trained masons are encouraged to start engaging with clients, and to market their skills to new clients in the locality. Masons who have reached the level of site foreman (C4) or entrepreneur (C5) are entirely responsible for their construction projects and for the salaries of their masons and apprentices.

By the end of 2016, through the Earth roofs for the Sahel program:

• 600 builders, entrepreneurs, and masons had been trained;

• 300 apprentices were working alongside them;

• 830 villages with at least one Nubian building.

The trained and experienced NV masons have no difficulty in finding clients and marketing their skills, as the demand for new NV constructions is currently outstripping the supply of skilled builders. And quite a few of the more ambitious NV builders and entrepreneurs are working on AVN pilot projects outside the Sahel (Zambia, Madagascar, Rwanda, etc.).

1.3 A Market: NV Housing

AVN’s mission is to promote the Nubian Vault, for as many beneficiaries as possible. To do this, the Association first trains and guides extension agents to “pump-prime” local markets, starting from a base of pilot villages, evolving into pilot zones, and then into entire regions. The pump-priming process starts with the identification of local “champion” and supporters and the running of promotional meetings at village level.

Objective over the next years is to promote national self-sustaining markets in NV housing by multiplying local, regional, and national initiatives through creating regional centers and setting up franchise partnerships with other NGO’s and development organizations.

The majority of AV’s resources (~80%) target our main priority groups of “bottom of the pyramid” families surviving in an informal economy in rural and semi-rural sectors.

By 2016, with an average annual growth rate of 32% since the start of the Program in 2000:

• 2000 construction sites;

• 79,000 sqm realized;

• 25,000 people now use or live in a NV house or building;

• 2,500,000 € generated on the local market (Figs. 2 and 3).

  Fig. 2

  

  Mud bricks. Photo credits: All pictures are made by caravatti_caravatti architetti

  Fig. 3

  

  Mud bricks production. Photo credits: All pictures are made by caravatti_caravatti architetti

1.4 Technical Overview

During the last fifteen years, AVN has successfully introduced a simplified, standardized version of this ancient technique. This standardized NV technique is:

• roofs are exclusively vaulted (no domes) and can incorporate a traditional flat roof terrace;

• vaults are a standard width (3.25 m), made from mud bricks of a standard size;

• a guide cable is used to define the curvature of the vault;

• walls are a standard thickness, and openings for doors and windows a standard size;

• plastic sheeting is incorporated in the roof to reduce water penetration and erosion.

The major cost element in using the VN method is labor, often provided by family members and neighbors on an exchange /barter /self-build basis, thus keeping cash in the local economy; the raw materials (earth, rocks, water) are locally available and ecologically sound; construction with mud bricks and mortar is traditional in the Sahel region—the innovation of vault construction can easily be incorporated into existing practice.

Building a Nubian Vault house

Learning to build a vault, however, is a skill that can only be acquired through experience on a NV building site. Timing is crucial: Construction can only occur during the dry season (September–May in the Sahel) and must be completed before the seasonal rains start. Fortunately, the dry season is also the time when there is little agricultural work to do in the village fields, and men are available to help as unskilled labor or to train as apprentices.

Obtaining building materials

Advance scheduling of the sourcing of building materials (earth, water, rocks) and the making of the mud earth bricks is essential: Ideally, when the team of NV masons arrives to start work, the rocks for the foundations, the water and earth for the mortar, and the bricks for the walls should all be ready and on-site. Any delays here will not only cause problems between mason and client, but also run the risk of being unable to complete the house before the start of the next rainy season.

The foundations

Depending on the properties of the ground and the site of the building, foundations can vary from 40 to 80 cm deep; they need to be 70 cm wide for load-bearing walls and around 50 cm wide for the gable walls. They are filled with rocks, bound with an ordinary earth mortar. In sites where there may be strong flows of surface water during the rainy season, the foundations should be raised 10–15 cm above ground level.

Load-bearing walls

Load-bearing walls which carry the vault are 60 cm thick and are made up of rows of super-imposed mud bricks. Each course is made up of a row of bricks laid lengthwise alongside a row laid width wise, using an earth mortar. The orientation of the bricks alternates with each course.

Recesses and openings are built into the thickness of the walls (doors, windows, cupboards, alcoves, and shelving). These are headed with arched lintels (built over oil drums as a temporary support); their use can be modified according to the needs of the owner. These are built before construction of the main vaults starts.

Gable walls

“Gable walls are built in courses of bricks laid lengthwise and are around 40 cm thick. They are raised so as to lean slightly inwards (by around 1.5 cm for each meter of height).

Construction of the vault

Flat bricks (24 cm × 12 cm × 4 cm) for the vaults are made in advance from good quality earth, such as that traditionally used for building granaries.

No formwork or shuttering is used to support the vault during construction. The mason, using a mortar made from the same earth as the bricks, starts the vault by laying the first courses against one of the gable walls. A cable is stretched between the two gable walls, at the height of the base of the vault. This defines the central axis of the vault, and a cord fixed to a sliding ring on the cable acts as a guide to ensure that the mason maintains a constant radius for the vault. Toward the top of the vault, the mason adds a couple of fingers width to each joint to develop an ogival (catenary) shape.

Buttresses

are formed on the completed vaults by raising the side walls by 8–10 courses of large bricks, and by filling the gap so created with plain earth. The height of the buttresses depends on the client’s needs—many prefer to raise them high enough to make a flat roof terrace over the vault (and the flatter the roof, the more resistant it is to erosion during the rainy season).

Finally, the roof is waterproofed, using plastic sheeting (locally manufactured, costing around 0.60 €/sqm), over a smooth coat of mud mortar. The sheeting is then covered with a rendering of enriched mud mortar (using traditional adjuvants), which both protects the plastic from damage by the sun, and provides additional protection against heavy rains.

External walls

are composed on earth brick walls, to use a thin cement rendering (very common in the Sahel regions), or a mix of tar/sand/earth/lime, which gives a very attractive finishing coat.

Regular maintenance and re-rendering with enriched earth mortars is in fact sufficient to guarantee the durability of the buildings.

Interior finishes

Depending on the resources and the tastes of the owner, various options are possible. Colored or plain lime washes are inexpensive to apply to the interior walls and help to reduce insect infestation. Installation of an electrical supply during construction is straightforward as well as interior showers, tiling interior or partition walls (20 cm thick) can be fitted.

The roof

Clients wishing to reduce regular maintenance to a minimum can, as an alternative to enriched earth, use a final rendering coat of thin fibro-cement mortar over an earth base. It is advisable to wait one year after construction before doing this, to allow for any settlement to occur (Figs. 4, 5, and 6).

Fig. 4

Nubian Vault construction site. Photo credits: All pictures are made by caravatti_caravatti architetti

Fig. 5

Bolmò_Republic of Mali Nubian Vault interior. Photo credits: All pictures are made by caravatti_caravatti architetti

Fig. 6

Ngolofalà_Republic of Mali Nubian Vault. Photo credits: All pictures are made by caravatti_caravatti architetti