Rammed-earth technology offers a promising solution to Kenya’s housing hunger
Kenya’s growing population continues to increase the demand for housing, as young people flock to urban centres in search of jobs.
The National Commission for Science, Technology and Innovation’s (NACOSTI) National Research Priorities 2018-2020 indicates that the urban population stands at 12 million people, representing about 31.8 percent of the total, while the urbanisation rate is 4.4 percent, equivalent to 500,000 new immigrants every year.
This rapid urbanisation has occasioned numerous challenges, including the increased demand for infrastructure and housing.
One major repercussion of the shortfall in formal housing in urban centres is that low-income residents and other vulnerable groups resort to inferior self-built structures, setting off an explosion of informal settlements and slums.
Rapid urbanisation has also sparked a sharp rise in property prices, with Nairobi, for example, ranked the second-highest priced city in Africa after South Africa’s Johannesburg. The need for decent, affordable housing is therefore unquestionable. Leveraging appropriate building materials and technologies (ABMTs) – a concept advanced by the Kenya Building Research Centre – is key to achieving the Government’s objective of building 500,000 affordable housing units by 2022.
ABMTs entail the use of affordable materials, efficient construction technologies and deployment of environmentally friendly building materials and techniques, especially those that are native to an area.
The Great Wall of China Rammed-earth technology is one such technique and has been in use across the world for thousands of years. Signs of its earliest use are still visible, especially in ancient monuments and architecture.
Other than walls, you might not even be able to tell you’re in a rammed earth home because in most other ways, it resembles a conventional house. The foundation, roof, wiring, plumbing and decorative features are installed in the same way as other houses
It is, for instance, a model that played a significant role in the construction of the Great Wall of China, which is at least 2,000 years old and about 21,200 kilometres long. Sections of the wall still stand today, though various stretches have been vandalised or eroded over time.
While use of the technology diminished as people turned to newer ones, some entities are now trying to revive it, because of its sustainable nature. Lengishu Luxury Home in Laikipia County, for instance, has embraced the use of sustainable materials, with stones excavated from the site used in laying the foundations.
Its walls are notably built using rammed-earth technology, with a combination of materials making the buildings blend with the surroundings and nature.
According to the Centre for Science and Technology Innovations (CSTI), a UNESCO-associated institution based in Nairobi, you can also sample what living in an earth-home feels like by visiting Kasigau Base Camp in Taita Taveta County. The camp is run by the Malewa Trust. “With enough advance notice, you can participate in making compressed soil bricks.
Building a community becomes more than just a construction activity, building a community turns into a learning activity about caring for Earth and designing spaces with individual personality,” says CSTI in its blog.
Several other local developments – especially eco-lodges – are adopting this technology. For example, it is used at Rukinga Ranch in Voi to build an eco-factory. In the rest of Africa, there are several projects that have used this technology. Hive Earth, a company in Ghana, for instance, uses the technology to build one-bedroom homes for slightly over Sh500,000 ($5,000).
The technology has also been deployed in the construction of the Library of Muyinga, at a school for the deaf in north-eastern Burundi. Rammed-earth blocks produced using compressor machines make up the walls. The architects used local labour.
The technology has gained popularity in recent years because its users, keen to conserve the environment, appreciate the use of sustainable, easily available and environmentally friendly materials.
Rammed-earth defined
Rammed-earth technology involves use of earth as a building material. Often, a suitable type of soil is mixed with clay, as well as other materials such as cement, and is then compacted and left to dry and cure. Cement is often added to stabilise the walls, and in such cases the technology is referred to as Stabilised Rammed Earth (SRE), as opposed to just Rammed Earth (RE). Panels are often used to create a rigid formwork to act as a mould for fashioning the structure of walls and giving them temporary support during the compaction. Plywood or steel panels are often used in this process, with the former preferred. Other materials, such as small quantities of cement or lime, and insulation and water-resistant finishes, may also be used. Many houses, particularly in rural settings, are built using a model similar to this technology, though often in its rudimentary form.
Earth, the main raw material, is easily obtainable and sustainable. Experts say that rammed-earth structures are more ecologically viable and environmentally friendly compared with those that use more cement, wood and steel
Rammed-earth technology, in essence, uses inexpensive local materials and sustainable resources, leading to little or no wastage. And while it may be deemed an ancient technology, its timelessness in terms of practicability, sustainability and viability, makes it invaluable in large-scale construction, such as in the affordable housing programme. This is because earth, the main raw material, is easily obtainable and sustainable. Experts on this technology say that rammed-earth structures are more ecologically viable and environmentally friendly compared with those that use more cement, wood and steel.
Moreover, because these structures are made using local materials, low amounts of energy and resources are needed in their production, and they generate minimal waste. For instance, to erect a structure, a foundation has to be dug first. But with rammed-earth technology, the excavated soil can be improved and reused in building the walls. This keeps the costs and the energy used low.
Structures built with rammed-earth technology resemble other conventionally built properties in virtually all aspects. The foundation, plumbing, electricity connections, roofing and decorative features are installed in just about the same way. Homes built using this technology, nonetheless, tend to have considerably thicker walls, and due to their good thermal mass, the wider walls imbue the houses with a general quietude and comfortable feel, depending on the climatic conditions. Such buildings are slow to heat up during a hot day and tend to cool slowly at night, when weather conditions outside are chilly. Strength and durability are important in any building, and rammed-earth technology makes these qualities possible, given the typical width and sheer compactness of the walls.
As a result, these structures require low maintenance, with experts ruling out any extensive repairs for at least 10 years. Structures built using this technology are also deemed safer, more people-friendly and comfortable to live in, as there are hardly any chemicals incorporated into their construction. As for fire safety, rammed-earth walls do not have any flammable components and thus have excellent resistance. Their resistance to vermin attacks is also good, because there is nothing in the material to attract or support pests.
Buildability and cost
Once the walls are up, pipes for water and wires for electricity can be laid the same way as in masonry buildings, but with caution not to tamper with the surface finishes. While basic materials for a rammed-earth structure are readily available in Kenya (soil and clay), cement and formwork or moulds may have to be transported over long distances, and this can raise environmental and economic costs. The builder may also need to test the local materials and the mixes to be used.
One way to control costs is to design walls as simple panels. Using human power to ram materials and simple wooden formwork is another way of keeping costs and use of energy down. Human labour is readily available both in urban and rural areas.
Though it has existed for many years, rammed-earth technology had not gained full acceptance in Kenya’s modern construction industry. The technology had, in fact, at one time been disregarded in most parts of the world.
Builders across the world are, however, now embracing and adopting it because it is environmentally sustainable. The reemergence of this technology rests on several factors. These include the fact that it requires little water, which is often a major consideration, especially in dry areas.
The technology also requires fewer other resources, such as aggregates or additives, to improve its properties. Earth, the main raw material, is easy to acquire and use. Homes built with this technology have good properties, including insulation due to their high thermal mass in hot conditions, and the buildings do not emit substantial harmful gases.
Rammed-earth walls are also maintenance-free and have a distinctive finish as they express sedimentary compaction lines that inform a simple and natural texture. There is therefore no need to finish the walls with plaster, wallpaper or tiles, which cuts the costs during construction and throughout the life of the building.
The structures also have noise-reduction properties and the walls are fireproof and strong. Replicating these benefits in Kenya, where there is a great need for more affordable units yet resources are limited, could prove quite appealing to the Government.
A key downside of the technology is that it may be labour intensive. But its bonus is that it provides jobs for young people.
Challenges and way forward
The technology is labour intensive, with the soil often requiring to be mixed in correct quantities. Rammed-earth structures are also most ideal in areas with little rainfall, because heavy amounts of rain could destabilise the slightly porous nature of the walls over time.
There are, however, water-resistant coatings that can be incorporated to protect the walls, making them apt for such conditions. To provide more protection for walls in areas that receive heavy rainfall, roofs can be made to hang over them. Another drawback is that because the technology is labour-intensive, there is a need to invest more in machinery and equipment, which means additional costs.
The walls also require precise measurements during construction, as once a mistake is made, correcting it would be difficult, unlike in other models such brickwork where a single improperly fitted brick can be easily removed and reinstalled. Also, because the walls are often wider than the standard ones, such buildings tend to take up more space, a downside in situations where space is increasingly becoming limited.
Why rammed-earth?
- Cost effective: Most of the materials are locally available; construction costs are low.
- Ease in construction: Little or no machinery is required, hence many people can use the technology.
- Insulated and warm: Houses maintain stable internal temperatures because they ‘breath’.
- Safety: Houses made from this technology are safe from fire.
- Environmentally suitable: Nearly all the materials used are biodegradable.
- Low embodied energy: Transport is greatly reduced, which saves energy. Compunction can also be done manually.
- Aesthetics: Some of the most beautiful houses are built using rammed-earth technology which blends with nature
These drawbacks, however, do not overshadow the long-term benefits of rammed-earth technology as long as due diligence is observed during construction. And with the advent of modern technologies and the prospects of more innovation, this technology is bound to improve.
For instance, modern soil-testing technologies are now available to identify the right compositions for use. There is also a better understanding of the sciences involved — for example, small amounts of cement can be added to the mix to enhance robustness — better structural designs and proper regulatory policies.
Governments are increasingly concerned about the threat of global warming and climate change. While the more engineered and processed variants of rammed-earth technology may have some degree of greenhouse emissions, its most basic form is largely safe.
In the end, as the Government races to deliver 500,000 affordable housing units by 2022, the route to this goal is literally down-to-earth: bringing natural homes into the 21st century through rammed-earth technology.
Recycling plastic into bricks that are stronger than concrete
Nzambi Matee hurls a brick against a school footpath constructed from recycled plastic made at her factory in Nairobi. It makes a loud bang, but does not crack. “Our products are five to seven times stronger than concrete,” says Matee, founder of the Nairobi-based Gjenge Makers which transforms plastic waste into durable building materials.
“There is that waste they (people and factories) cannot process anymore; they cannot recycle. That is what we get,” Matee says, strolling past sacks of plastic waste.
Matee gets the waste from packaging factories for free, although she pays for the plastic she acquires from other recyclers. Her factory produces 1,500 bricks each day, made from a mix of different kinds of plastic. These are high density polyethylene, used in milk and shampoo bottles; low density polyethylene, often used for bags that pack cereals or sandwiches; and polypropylene, used for ropes, flip-top lids and buckets.
Our products are five to seven times stronger than concrete. There is waste people and factories cannot process anymore; they cannot recycle. That is what we use to make plastic bricks
There is, however, one variant she does not work with – polyethylene terephthalate, or PET, commonly used for plastic bottles. At her firm, the plastic waste is mixed with sand, heated and then compressed into bricks, which are sold at varying prices depending on thickness and colour. The common grey bricks cost KSh850 per square metre, for example.
Matee, a materials engineer who designed her own machines, says her factory has recycled 20 tonnes of waste plastic since its founding in 2017. She plans to add another, bigger production line that could triple the capacity, and hopes to break even by year end. Matee set up her factory after she ran out of patience waiting for the Government to solve the problem of plastic pollution.
“I was tired of being on the sidelines,” she says.