Keywords: Vernacular, Stone Construction, Sustainable development
The following discussion presents volcanic stone as a viable walling material in areas where it is abundant. Kisoro, Fort Portal and Bushenyi located in Southwestern Uganda are areas endowed with abundant volcanic stone. However, area residents still opt for brick walling despite the poor soils in those areas. The poor soils produce lower quality bricks compared to the fired clay brick from other areas especially around the Victoria basin. Natural stone possesses physical properties suited for structural walling yet in Uganda it is habitually specified for its aesthetic finish (floor surfacing and wall cladding). In comparison to Compressed Earth Block (CEB) and Compressed Soil Blocks (CSB), stone has not been explored enough as a potential front-runner among sustainable walling alternatives. Further, little is being done to empower local communities to meet their own aspirations as industry, economics and urban development conspire to interrupt the transition to sustainable development particularly with regards to how environmentally unfriendly materials like fired brick are propagated.
The use of stone in construction is not completely alien to our context. According to Nnamdi (1997), stone construction in Africa dates back to over 10,000 years ago. In fact, Shadmon (1996) writes that Stone was used for construction way before man ever started using metallic tools. Stone construction in Africa was popular in hilly parts of Africa creating what was known as the “hill style”, Nnamdi (1997). More recently, residents in the hilly areas of Bunyaruguru and Kasese have constructed and actually live in stone buildings as shown in Figure 1. In parts of Kabale stone construction is evident in their stone garden perimeter walls, and stone cooking fireplaces.
Figure 1: Stone Cottage in Fort Portal and abundant stone in Southwestern Uganda
Fired brick is not indigenous to Uganda’s material palette, in fact it was never used, at least not until a century ago, when the biggest Cathedrals were constructed at Namirembe and Rubaga (Moon, 1994) under stellar supervision even during material production. Today, the local brick industry is highly unstandardized and because of this there is an inconsistent quality of bricks most of which are irregular. Further, some bricks are made from poor quality soils (locally know as kifufu) and are significantly weaker than the paying public expects. Irregularities in brick configuration have led to the wasteful use of mortar as the masons attempt to deliver straighter walls. Additionally, weaker bricks contribute to heaps of debris noticed on numerous construction sites – a topic deliberated upon previously on this blog (see Building and Materials: waste less, gain more, check the ecological footprint, October, 2015).
Indeed, potentially viable materials and construction techniques in rural societies are not being explored for their economic and environmental merit. Unfortunately, architects in practice are not helping the situation. Most architects in the country persistently avoid rural commissions because few, if any, people there can afford their professional fees. As a consequence, the low-skill level fundis and draftspersons that take on these rural projects generally work with a standard brick palette as taught in technical schools.
The cost of brick construction is even higher in the mountainous areas of Southwestern Uganda, even worse, where good clay soils hardly exist. As a result, bricks are transported large distances to service these areas further increasing the economic and environmental cost of construction. Brick transportation in the popular small to medium gasoline trucks over rough roads could consume as much as 5MJ/tonne for every kilometre (Fraser et al, 1995). At this rate, each truck on a regular 100km trip uses the same fuel equivalent to burning 100kg of charcoal. Transportation delivers an avoidable carbon load of up to 0.0741 KgCO2 per kilometre (Quashning, 2016).
Reducing the cost of construction is crucial for the success of vital infrastructure such as access to housing. “The cost of an average home mortgage in Uganda is about $30,000” Muhumuza (2016). However, according to the World Bank development indicators (2016), Uganda’s Gross National Income is $670. On a monthly basis, that is an average of $56. This means that on average a Ugandan committing upwards of 30% of their annual income to service a mortgage, would require 144 years for one to pay off the loan. These sums are inflated when interest is compounded. This indicates that even a middle-class Ugandan would need to spend well over 50% of their income to afford decent housing. Yet still, low cost housing in Uganda is considered by Ministry of Lands, Housing and Urban development, to be that which doesn’t exceed more than 30% of the homeowner’s income (Muhumuza, 2016).
There are three dormant volcanoes in Southwestern Uganda and according to Shadmon (1996), in the eruption of a volcano, as hot lava reaches the earth’s surface, it quickly cools down, forming crystals of igneous volcanic rock. Some of these rocks include andsite, basalts, purnice, and rthyolite. It is important to note that any one of these stones have a higher compressive strength than the popular fired brick. Take for example basaltic rock that is most abundant in these areas, has an uniaxial compressive strength ranging between 12-63Mpa, (Schultz, 2012) – which is higher compared to the average compressive strength of fired brick that ranges between 5-10Mpa.
Interviews revealed a general perception among residents that stone construction is expensive. Stone is even referred to as the rich man’s material. Residents report that, stone construction requires a lot more sand and cement mortar than fired brick. Also, due to low popularity of the material, skilled masons in the area are rare and expensive. Interviews further revealed that the construction process takes a long time owing to a longer duration required to dry the huge chunks of mortar. The delicate process of laying the uneven stone to form regular walls, also contributes to a prolonged construction process.
The residents say that before the popularity of brick in the area, vernacular architecture was constructed using mud and wattle like in other indigenous communities of Uganda. However, unlike in other areas, people in Kisoro added small volcanic stones to the mud to create firmer walls. The walls were then finished with chalkstone dissolved in water to create a smooth surface. Today, there are few stone buildings in the area mostly owned by the rich. The difference being that the wealthy use sand and cement, yet the rest use mud mortar. However, the result is not sturdy and for this reason, some residents in search for better quality buildings opt for fired brick rather then use stone with mud mortar.
One good practice example in a similar context is Butaro hospital by MASS design group architects located in Butaro, Rwanda just a few kilometers from Kisoro with similar climate, terrain and abundance in volcanic rock. This project made use of the local volcanic rock, but also is sensitising society through the quality of the physical structure, that there is potential in this long-ignored material. As a result, a new industry of stone dressing, marketing and construction has been able to kick off in Butaro, creating jobs that otherwise didn’t exist as Benimana (2016) explains. Similarly, the artisans who hand-crush stones for aggregates in Southwestern Uganda can be further commissioned to shape volcanic stone to more regular blocks that can be assembled with less mortar. Further, in this same context, there is an existing trade of hand-crushed stones for construction aggregates. Stone crushers stand a chance to make additional income from stone dressing like their counter parts in neighbouring Kenya.
Progress in material production comes down to equipping communities with the necessary knowledge and skilling. Architecture Schools need to educate built environment professionals to be more open-minded and take pride in the heritage of this country, and the readily available materials or opportunities that our context has to offer. This can be achieved by questioning how we build and who builds if we are to transform rural communities all over the world.
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