Africa stands at the crossroads of unprecedented urbanisation, with its population expected to reach 2.4 billion by 2050. This demographic surge is poised to drive an 80 per cent increase in construction, predominantly in urban areas, including slums. The manner in which this urbanisation unfolds is critical, given that buildings currently contribute to 37% of energy-related emissions and consume 50 per cent of extracted materials globally.
As we navigate this trajectory, the significance of the Global Alliance Roadmap for Buildings and Construction in Africa cannot be overstated. This roadmap is not just a guideline; it's a compass guiding us towards sustainable urban development in the face of a housing deficit projected to hit 53 million by 2040.
The roadmap underscores the urgent need to address emissions associated with building materials, which are projected to rise from 3.5 to 4.6 gigatons of CO2 equivalent per year by 2060. 80 per cent of African building stock expected for 2040 is yet to be built. Buildings must evolve to be not just shelters but guardians of our environment and resources.
In the Rwandan context, ADHI has set a ground-breaking precedent in emission reduction, both in embodied upfront carbon and operating carbon emissions. The BWIZA Riverside project stands as a testament to our commitment to sustainable urban housing.
The conventional approach to constructing 53 million homes, averaging 100 tonnes per unit, would demand a colossal 5.3 billion metric tonnes of materials. ADHI's innovative solutions reduce this to a mere 795 million metric tonnes, slashing volume by 85 per cent while ensuring stronger and more durable homes. The impact of this reduction is immense, both in terms of resource consumption and carbon emissions.
Consider the staggering numbers: The conventional approach would generate 4 billion tonnes of CO2 equivalent, whereas ADHI's approach would cut this to 848,000 million tonnes, resulting in a remarkable 3,152,000 tonnes of CO2 emission reduction. Moreover, ADHI's certified EDGE IFC from the World Bank solution reduces construction waste by a staggering 95 per cent, ensuring minimal environmental impact compared to conventional methods. This waste is further reusable and recyclable compared to the conventional construction method that generates on average between 20 per cent to 40 per cent construction waste.
Land use change for 53 million homes at reasonable density would require approximately one million hectares. ADHI's use of Reinforced Soil retaining walls, crafted from locally excavated soft soil, reduces embodied carbon by a staggering 99 per cent compared to conventional reinforced concrete and imported rocks.
In comparison, a reinforced concrete retaining wall of 5.50 metre height and one metre long has 845 tonnes of embodied carbon while the same size wall in reinforced soil used by ADHI has only 0.229 tonnes of embodied carbon. These numbers should shock anyone once laid side by side in comparison on applicable projects. Take the case of Bwiza Riverside, ADHI has built a total of 7,000 square metres of this reinforced soil retaining wall carrying a total of 291.45 tonnes of embodied carbon. Had ADHI constructed the wall in the normal conventional method of reinforced concrete retaining walls, a staggering 1,075,448.40 tonnes of embodied carbon would be a result of this decision compared to 291.45 tonnes of embodied carbon. As shown in Table 1, the necessary material volume and CO2 emissions for every one metre of structure length are outlined.
Table 1: Necessary material volume and CO2 emissions for every 1 metre of structure length.
Figure 1: Graphic comparing the estimated CO2 emissions from each structure for one meter of structure length.
The BWIZA project, ADHI's ground-breaking initiative, achieved an 80 per cent green surface in land use change, embracing the sponge city principle to reduce runoff water volume. Rainwater is treated for reuse, and on-site sewage water treatment is a testament to our commitment to holistic sustainability. The selection of volcanic pavers compared to concrete pavers also draws the attention to the huge embodied carbon reduction. General building cement itself has a much higher kgCO2/tonne value, in fact, almost 20 times that the value of stone. See Figure 2 below.
Figure 2: Graph showing embodied carbon comparing stone and concrete pavers
Furthermore, ADHI significantly reduced quarry aggregate use by replacing it with EPS beads that are 98 per cent encapsulated air, making structures lighter and more insulated. This reduction not only lessens the dependency on aggregate for construction but also reduces the quantity required for concrete, leading to lighter buildings that require less heavy structural reinforcement, a common feature in orthodox construction methods.
Rwanda's leadership and progressive vision have catalysed ADHI's practical and pragmatic solutions for GHG emission reduction, resource sustainability, and affordability. Furthermore, the ADHI ecosystem delivers 14 out of the 17 United Nations Sustainable Development Goals. The carbon credits generated by these initiatives could single-handedly fund the country's infrastructure and housing finance needs.
In practical terms, the remarkable reduction of 1,075,150 tonnes of embodied carbon in the innovative soil reinforcement retaining wall at Bwiza Riverside alone could translate to a substantial economic benefit of $53,757,500 in the carbon market, assuming a price of $50.00 per tonne. Beyond the impressive environmental impact, these potential revenues underscore the financial viability of sustainable construction practices, showcasing the dual benefits of responsible urban development.
In conclusion, Rwanda's remarkable success in pioneering sustainable urban housing development through ADHI's innovative solutions serves as a beacon of inspiration for the entire continent. By showcasing the tangible benefits of responsible urbanisation, Rwanda has not only addressed its housing deficit but has also set a transformative precedent. This success story stands as a powerful testament to the feasibility and desirability of sustainable practices, poised to inspire and catalyse similar initiatives across African nations, fostering a collective commitment to building resilient, eco-friendly, and socially inclusive urban landscapes for a prosperous future