The Nubian vault is transforming low-cost housing in West Africa

Something I have learned during this last year in Africa is how challenging roofs can be, especially for low-cost building projects. Traditional earth walls are easy enough to build with local materials, but sourcing wood for the roof is getting more and more challenging and expensive due to deforestation and population growth. One NGO from Burkina Faso that has found a unique and effective solution to this problem is the Nubian Vault Association, or Association la Voûte Nubienne (AVN). AVN works in five countries in West Africa where the organization promotes a traditional earth vault building technique that requires no wood, steel or cement: the Nubian vault.

AVN’s mission is to improve housing for as many people as possible and as soon as possible. Nubian vaults do this by providing more comfortable and durable but still affordable houses. By promoting Nubian vaults, AVN also contributes to climate change adaptation and mitigation, economic growth and education. AVN’s approach is not to build or donate houses but to train masons and sensitize populations to the technique, hoping to initiate a self-sustaining market in the process. Thanks to the work of AVN, thousands of people in West Africa now live in more than 2000 Nubian vault homes and the market for Nubian vaults is growing rapidly.

Emergence of the Nubian vault solution

Traditional roofs in Burkina Faso and many other drier countries of West Africa are flat earth roofs supported by a dense structure of wooden beams and branches. The wood can be very rough but a lot of wood is required to support the weight of the earth on top. People in these countries have been sourcing their own wood for generations, but now it is becoming increasingly difficult due to deforestation, desertification and population growth.

As traditional earth roofs have become more challenging, they have been been replaced by metal roofing sheets. These sheets are expensive, unbearably hot in the summer, cold in the winter, noisy during the rains, and often low quality. What’s more, the structure still requires wood, although much less than traditional earth roofs. Generally the wood is imported sawn timber and represents a major part of the building costs. Burkina Faso is one of the poorest countries in the world and finding the money to build a house is a struggle for many. Any added costs make quality housing less accessible to the masses.

AVN’s solution to the problem is earth brick vaults, more specifically a traditional vaulting technique from the ancient civilization of Nubia that was based in today’s southern Egypt and northern Sudan. The oldest Nubian vault still standing in Egypt is 3300 years old, which is a clear testament to the durability of the technique. The technique was first revived in the modern age by Egyptian architect Hassan Fathy in the 1940s.

AVN was started by a French mason and a Burkinabe farmer who built two prototype Nubian vault buildings in Boromo, Burkina Faso in 1998. The following year two larger Nubian vaults were built, and the Nubian Vault Association was formally founded in 2000 to facilitate the spread of the technique. Over the years, AVN has simplified and standardized the technique so that it can be easily and widely adapted.

From Burkina Faso AVN started expanding to other countries in the region and today the organization is active in four other West African countries, namely Mali, Senegal, Ghana and Benin. Every year 500 Nubian vault buildings are now being built in these countries by 400 specially trained masons. The majority of projects is rural housing, but there are also some schools, clinics, churches and mosques, as well as a small amount of urban housing.

The Nubian vault technique of AVN

There are many ways of building a brick vault. One of the main benefits of the Nubian vault technique is that it requires no support or formwork during construction. The Nubian vaults of AVN are built using small and lightweight unbaked adobe bricks and mud mortar. The bricks are laid leaning at a 60 degree angle so that the first bricks rest on the gable wall and successive bricks on the previous bricks. A guiding cable defines the central axis of the vault and it is used to check a constant radius during construction. The ideal shape is not a perfect semicircle but instead slightly elliptical at the top, as this shape is closer to the ideal catenary curve where all forces are in compression and the resulting vault is as strong as it can be.

The walls are also built with unbaked adobe bricks and thick walls are needed to support the vaults. The gable walls in AVN’s design are 40 cm thick and the vault supporting load-bearing walls 60 cm. The walls could probably be slightly smaller, but these dimensions are AVN’s standard for safety reasons, so that vaults can even be built by people with less experience and less supervision. Thick walls also make the houses very durable, while large stone foundations take care of the heavy loads and extend the lifespan of the buildings. Doors and windows are built with arched lintels using oil barrels as temporary supports. Adobe brick buttresses support the vault from the sides and make the exterior of the roof flat. This structure is even strong enough to support a second floor.

AVN has adapted the traditional Nubian vault design to the West African climate which is wetter than in Egypt. The roof is made waterproof with the help of a plastic sheet on top of a smooth mud coating, followed by at least 6 cm of plaster that protects the plastic from the sun. Tar and waste engine oil is mixed in with the clay plaster to make it stronger and waterproof. The flat roof slows down rainwater runoff and hence reduces erosion caused by rain. Both the roof and the walls do need regular maintenance such as replastering, but this practice is already a part of the traditional building culture, as I saw in Djenné.

AVN has slowly mastered the technique over the years and variations from the standard also exist. Larger communal spaces like churches or classrooms can be created by combining the Nubian vault technique with concrete beams and columns. AVN is also doing research to further improve the technique so that it can be even more widely adapted.

Improving housing conditions in rural West Africa

AVN’s main mission is to improve housing conditions and 80% of Nubian vault buildings are rural homes. But AVN doesn’t simply build and give away homes. What AVN does is subsidize the cost of Nubian vault homes, but it is the homeowners themselves who have to find the necessary finances and make the investment to build the house. One of the benefits of Nubian vaults is that the vast majority of materials, namely mud and stones, can generally be harvested locally for little or no cost. Most of the expenses go towards labour, and families can reduce the costs by making their own bricks or by providing free unskilled labour to help the mason. The only thing that actually needs to be bought is the plastic sheet protecting the vault from rain damage – the rest is just work.

Even though Nubian vault homes require no expensive materials, they are high quality. Thanks to the thick walls and roofs, Nubian vault houses are considerably cooler in the summer and warmer in the winter than concrete block houses with metal roofs. Nubian vault homes are also very durable and with proper maintenance they can last for generations. Both of these aspects add value to Nubian vault homes and make them good investments.

One of the reasons AVN is having such a great impact is that its designs respond to the needs and desires of the clients. Those who want and have the money can pay more for larger homes, smoother finishes and detailing, but it is not necessary. Leaving the house rough and small is more affordable and respects the rural context. Even if the house is simple and low-cost, the vaulted design has its own status thanks to its uniqueness. Nubian vaults are something the poor can afford but they are not associated with poverty, and so the poor can feel proud to live in Nubian vault homes.

Sensitizing people to the Nubian vault technique

A crucial part of AVNs work is convincing people that Nubian vaults work and that families should build and invest in them. AVN does this by going to villages and sensitizing people in order to raise awareness about the technique. Masons explain the technique and its benefits to the villagers and show pictures from existing Nubian vaults. It can be difficult to get started in new village, but once a key person with some influence in the village decides to build a Nubian vault, others usually follow. Most people who choose the Nubian vault do so because they know the metal roofing sheets are very uncomfortable.

Individual buildings and events can also have huge effects on changing people’s mindsets. In 2017 AVN received funding from the UN Food and Agriculture Organization to build an agricultural storage space for a farmers’ cooperative in Burkina Faso. The idea was that the indoor climate of the Nubian vault would keep the produce more fresh than the existing cement block and metal sheet store. The farmers were however skeptical and most didn’t want to take the risk of trying something new and used their old storage rooms instead. Bad weather and humidity caused a lot of produce to be lost that year, and it was the few farmers who used the Nubian vault who had the least losses. Next year everyone was using the Nubian vault store.

When sensitizing people, it is important to understand the context of each village, region and country. In Senegal the cement industry is very strong and there is more money coming from migrants so it is harder to find clients interested in Nubian vaults. In Mali there is a culture of community building and AVN masons can even get the locals to build each others’ houses for free. Meanwhile, in Burkina Faso even the most unskilled labour needs to be paid which adds to the cost of the house.

Training masons for a self-sustaining Nubian vault market

At the end of the day, AVN’s focus is not on building buildings but on training masons. More than 400 AVN masons have already been trained and another 400 are in training. Skilled mason train apprentices on-site and there is an apprentice at every work site, as is common in the culture. Whenever AVN goes to a new village to sensitize people and find new projects, they also find some new apprentices from that village. This is a life-changing opportunity for young farmers to emerge from poverty by learning new skills and a way to generate income.

AVN has 4 levels of masons, from apprentice to master. AVN has defined more than 100 skills that masons have to have to be qualified at and it takes a few years for masons to achieve all these skills. Most AVN masons have had no former construction experience or any other education and most are illiterate. To accelerate the learning process, AVN is now turning more towards training otherwise qualified masons in the Nubian vault technique.

It is important to note that AVN is a market facilitator, not a construction company. The masons are supported by AVN but they are working independently and directly paid by the clients. The masons are also responsible for managing the construction site and client relations. As most of the building costs are labour, a large proportion of the money goes to the builder, which makes being a Nubian vault mason profitable while also ensuring the money stays in the country and benefits the local economy.

AVN has made the Nubian vault technique easy to learn and simple so that it can be done with basic tools and so that more people can be reached. The technique has also been codified and standardized. The goal is to create a self-sustaining market that can spread naturally, and every year more and more Nubian vault buildings are being built in response to rising demand. The Nubian vault is slowly finding its position in the West African housing market where it has the power to change housing for the masses – built by the locals themselves.