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| 3-October-2024 |
There are many ways to reduce the embodied climate impact of construction (that is, to reduce the embodied greenhouse gas emissions – those generated by the construction, maintenance, and eventual demolition of a building, in contrast to the operational emissions produced during a building’s use).
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| Construction in progress. Photo by Akintunde Akinleye |
Take, for example, the embodied emissions of the Lagos reference building discussed in the previous post, Nigeria: meeting the need for housing. Here, the most important factor would be minimising the emissions from standard concrete and steel, but also minimising the lifetime need for recurrent fresh coats of paint. (Metal and paint manufacture are also chemically polluting in other respects.)
One way to reduce cement and steel emissions is to switch to renewable energy, something that needs to happen anyway across the whole of society.[1]
But Isidore Ezema and his colleagues note an unfortunate backwards step: in 2016 the main cement company in Nigeria – presumably, Dangote Cement – “announced a switch from the use of natural gas and low pour fuel oil (LPFO) to coal as the main energy source for cement production”.
This means that the energy-related emissions of producing cement will have risen. And that is just a small part of the problem. The larger challenge, in the production of both steel and cement, comes from their process emissions – the ones that are produced as a chemical by-product of manufacture.
These process emissions are usually categorised as hard to abate: that is, there is no straightforward replacement for the carbon-heavy methods used. (See my previous pamphlet for an overview of options for decarbonising cement and concrete, and decarbonising steel.)
With regard to steel, low-carbon steel manufacture requires enormous levels of capital investment, quantified in trillions of dollars. This therefore undermines the profit structures of a highly competitive world market for steel, and is unlikely to be introduced without enormous pressure from governments.
With regard to cement, there are some promising low-carbon approaches to cement and concrete manufacture. Less promising alternatives rely on CO2 capture and storage (carbon capture and storage, CCS). CCS is unproven at scale, technologically.
Unfortunately, as with steel, the options for wholly low-carbon cement all appear unlikely to be become economically attractive, or even accessible, anytime soon, without massive state assistance.
The crux of the problem for cement is that bog-standard cement is incredibly cheap, and available at local level.
The imperative for cheapness would require high-tech manufacturers of alternatives to scale-up and globalise production and distribution down to the local level, while also foregoing any significant remuneration for their novel intellectual property.
Any viable low-carbon alternatives to cement and concrete will need to be made universally available for off-brand “generic” manufacture, and, even then, subsidised so that they are cheaper than the traditional versions.[2]
Alternatives for cement and concrete might additionally require a high, globally-enforced carbon price in order to fully displace bog-standard cement and concrete with a no-emissions alternative.
So, to the extent that it requires steel and cement, a mass housing programme in Nigeria would require massive subsidy – and likely still depend to a large extent on emissions-intensive steel and cement.
Depending on how it is used, cement can be replaced with calcined clays, which become cementitious when heated, but do not require such high temperatures as cement. This reduces both energy-based and process emissions.
These natural pozzolans (materials based on silica and aluminium oxides) can be used on their own, or used to replace some of the cement in concrete. This latter method can reduce the embodied emissions of concrete by up to 29%, according to recent research.
Pozzolans are also quite plentiful in Africa, especially in the Rift Valley in the East, and in Nigeria. However, they remain under-utilised. They could reduce the need to import cement from abroad. The previous government’s Energy Transition Plan (discussed in the linked post, Nigeria: bringing energy to homes) proposes using calcined clays as a partial substitute for clinker in cement manufacture.
However, there remains a need in Nigeria, and across all nations, to minimise the need for steel and cement in the first place.
Both materials need to be effectively rationed on a “contraction and convergence” basis, and based on essential needs.
In Nigeria, this means confining the use of emissions-intensive steel and cement to situations where they are strictly necessary – in the delivery of essential high-quality homes and infrastructure.
Other ways to reduce unnecessary construction and embodied emissions include avoiding unnecessary demolition for new construction, re-using materials, and increasing material efficiencies in construction.
No building or infrastructure should be demolished unnecessarily, if it can instead be usefully retained, and (if necessary) retrofitted to improve operational standards such as passive cooling.
“Build light” is an overall ethos. Construction elements can be specified to be less heavy, and to require less structural support, less concrete and steel, and fewer embodied emissions.
Surfaces and materials should specified with a view to minimising the need for maintenance and repair.
Techniques of circular construction will also be vital, with materials maximally recycled and recyclable, and buildings capable of being deconstructed and their components fully reused.
Use of adhesives and paints should be curtailed, in order to facilitate deconstruction and re-use. Use of “self-finishing” materials further reduces the need for painting.
Metals can already be readily recycled – although, like manufacture, that uses a lot of energy. Demolition concrete and cement can be downcycled to provide aggregates for further construction – but the diminution of quality is wasteful in itself, and it should never be assumed that new concrete and cement are required in place of old.
Alternative materials
Low-carbon materials will be crucial for reducing the emissions intensity of construction. Moreover, in many circumstances they will be superior to the mass-produced, imported, mainstream alternatives.
Among the most promising materials, especially for Nigeria, are “traditional” ones such as rammed earth, clays, unfired bricks, stone, and plant-based products such as wood, bamboo, and hemp.
All these have very low embodied emissions (see the materials pyramid mentioned above, and part 8 of Decarbonising the Built Environment: a Global Overview).
Plant-based materials contain biogenic carbon – carbon absorbed from the atmosphere during the plants’ growth phase – and are frequently carbon negative, i.e. they are associated with drawing down carbon from the atmosphere, rather than adding it.
Among these, new forms of mass timber such as cross-laminated timber (CLT) can be very effective for load-bearing structures. Once the emissions from manufacturing are included, CLT remains net negative for greenhouse gas emissions, and a potentially vast storehouse of carbon. CLT can in many instances replace structural steel and reinforced concrete.
Bamboo is a traditional load-bearing material that is grown widely in Nigeria,[3] and can be used instead of structural steel and reinforced concrete in many instances. It grows fast, and therefore absorbs CO2 from the air rapidly, fixing it as biogenic carbon. It can also be processed into CLT – although the additional emissions involved presently take the embodied emissions of bamboo CLT almost as high as those of steel, on a per-kilogram basis.[4]
Hemp is a bit of a wonder material – it grows fast as well, making it an excellent store for carbon from the atmosphere. It can be grown in untilled soils, and is harvestable within just a few weeks. Hemp is excellent at rejuvenating degraded and polluted soils, boosting subsequent crop yields, and can be used in rotation as a “break crop”. It is a very good natural insulation material.
Hemp stalks can additionally be processed into hempcrete, a natural concrete substitute. Though it has only 5% of the compressive strength of traditional concrete, it weighs only about one-seventh as much – good for building light. Its other advantages include high thermal inertia, that it is highly flame-resistant, can be mixed on site and is recyclable. On the downside, hempcrete produces process emissions like cement does. However, these are roughly balanced by the CO2 absorbed by the hemp in its growth phase – making hempcrete roughly carbon neutral at point of construction.[5]
Hemp is perfectly cultivable in Nigeria. At present, though, hemp production, processing, and marketing remain illegal.
CLT or bamboo can be paired quite readily with other plant- or earth-based materials, to provide alternative building systems to conventional steel and concrete. You can even construct highrise buildings out of CLT (albeit with a concrete base, elevator shaft and stair wells in this instance).
Two inter-related threats with regard to using plants for construction in Nigeria, however, are the risk that this will threaten domestic food security, by displacing food crops, and that it could serve to accelerate deforestation.
Food insecurity is already exceptionally high in Nigeria and this has recently worsened, due to food price inflation. Deforestation also remains a severe problem.[6]
Any use of plants in construction needs to be pursued as part of a holistic and sustainable approach to land management and food security, and in the context of a continual expansion of fertile soils and forest cover, in the face of rising temperatures.
One holistic approach might be to limit the use of plants for construction to the scale of forest biomass that is reclaimed from the desert, or saved from domestic consumption through the electrification of cooking.
On the other hand, cultivation of such crops as hemp and bamboo could, in itself, help to remediate degraded land, if pursued in the right way. That way it would be win-win, with construction materials helping to reverse soil depletion, and reinforce food security.
Stone, earth- and mud-based materials are also crucial alternatives to cement and steel.
Ten per cent of Nigeria’s population already live in buildings constructed out of earth- or mud-based materials. Traditional masonry technologies such as adobe, mud blocks, and rammed earth have a long history throughout West Africa – where they are traditionally made out of laterite soils and pebbles, with dung or straw sometimes added.
These materials have often been disparaged as associated with poor moisture performance, poor durability, high maintenance, and low social class. However, earth-based masonry can be an ideal construction material when it is implemented well, due to its high thermal mass and load-bearing potential.
Compressed earth or clay blocks and bricks, unfired and sun-cured, have an important role to play in Nigerian construction. Ideally, cement-based mortars should be avoided, or alternative low-carbon binders used instead.[7]
Stone is a very effective, and ancient, structural material. Depending on the availability of suitable stone, it can replace concrete and steel as a load-bearing material, in full or in part.
For instance, 15 Clerkenwell Close, an award-winning building in London, has a limestone exoskeleton to support the interior structure. Its embodied carbon is apparently 10% of what it would have been if steel and concrete were used instead, with modelled whole life embodied emissions of 335 kgCO2e/m2 – much less than the 589 kgCO2/m2 of whole life embodied carbon for the Lagos housing scheme assessed by Isidore Ezema and colleagues.
More strikingly still, the cost of the outer shell and core of the London building was about 50% of what it would have been, if concrete or steel had been used.[8]
One useful reference for alternative construction materials is a recent study on sustainable building materials in Africa, commissioned by the UN’s One Planet Sustainable Buildings and Construction Programme. Another document, from the UNEP and IEA, gives a global view of sustainable building materials.
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| Source: Ninni Westerholm (2023), Unlocking the Potential of Local Circular Construction Materials in Urbanising Africa. (United Nations One Planet Sustainable Buildings and Construction Programme) |
That One Planet study advances a good, programmatic concept for high-quality, high-density urban development, consisting of mid-rise residential buildings on the model of Paris and Cairo. The author, Ninni Westerholm, outlines how timber, bamboo, hemp, straw, earth, clays, and stone, could all be deployed to provide mass housing. She emphasises the role of local labour, local materials, circularity, and thermal comfort.
The core load-bearing structure of these 4-to-5 storey housing buildings should be constructed wherever possible from renewable materials, such as high-strength manufactured timber, sourced from sustainably managed forests, the study proposes.
When those materials are not available, steel and/or concrete could be used instead in a measured and efficient way. All load-bearing structures should be designed so that they can be disassembled and re-used.
The “infill” for exterior walls and the façade would use hempcrete or compressed earth bricks – both of which are reusable – with the façade designed to minimise maintenance. Internal walls could similarly use natural, local, reusable materials. Flooring, roofing and other structures would similarly prioritise low-carbon materials and circularity.
All building services, such as plumbing and sanitation, electrical wiring and communications, should be made accessible.
Traditional construction materials and methods are usually less capital-intensive than industrial ones. Irrespective of the high cost of cement in Africa, lower capital-intensity may well make traditional construction processes less profitable and less worthwhile, from the perspective of capital.
Nevertheless, artisanal forms of construction such as those outlined above, are rarely more expensive than prevailing modern methods of construction. The difference is simply that a greater share of production costs go to labour than to capital-intensive industry.
This makes for good sources of local work, and it helps local communities, since a greater proportion of capital spending ends up circulating in the local economy.
Traditional materials can also support the incorporation of local knowledge – for instance, regarding what materials work well locally in relation to factors like climate, and what can be sourced locally. Engaging and elevating local craft skills is of value in its own right.
Traditional and modern industrial methods can used in tandem. They can also be combined, through the use of pre-fabricated units, and “flying factories”.
The One Planet urban construction concept for Africa suggests a division of labour according to capital- and labour- intensity:
The load-bearing and structural elements in a building, the author suggests, would tend to benefit from more industrially-coordinated, capital-intensive methods of construction – and therefore from larger companies bringing in machinery and expertise. Similarly, building services would often be connected by a utility firm or large outside contractor.
On the other hand, all internal walls, non-load-bearing structures, services, and finishing, could be provided by non-industrial and traditional methods. (The author terms this “unskilled labour”, but I think that is inaccurate. In many cases, these are highly skilled, artisanal forms of craft labour.) Modern construction norms would have a role, but they would not dictate the overall programme of construction.
In my view, the economic logic of construction should not be conformed to private profit: the focus instead needs to be on high quality, well-paid jobs – and on putting money into communities.
So long as the cost of imported goods and foreign capital investment can be held down, there is every reason for the Nigerian government to spend its own currency into the economy, on a mass housing programme, so long as this does not push on inflation. (See parts 2 and 3, above.)
Operational emissions and cooling
Finally, there is potential for reducing energy consumption in Nigerian homes, and the resulting operational emissions.
This is not about cutting down on the uses to which people put energy (defined by researchers as final energy use), such as cooking, lighting and heating. This is about providing for people’s needs more effectively and efficiently, reducing the throughput of energy and avoiding waste. (See also Decarbonising the Built Environment, part 9 and part 10.)
Some opportunities for reducing operational emissions while making people’s lives better – including switching to electric cooking – are covered in the linked post, Nigeria: bringing energy to homes. Here I cover an issue that has to be dealt with even as homes are getting built: thermal comfort.
Households in Nigeria presently consume an absolutely tiny quantity of energy on supplemental space cooling in the home. At the same time, global warming is forcing temperatures up to unbearable levels.
Lagos is among the most vulnerable of Africa’s major cities to increases in extreme heat. The need for adequate protections is only increased by the housing deficit, and a rapidly growing urban population.
Demand for air conditioning units across Africa is forecast to rise, as more people gain access to electricity and temperatures increase, according to the UN. It will be tragic if Nigerians are compelled to use air conditioning en masse. Not least, it will needlessly increase people’s need to consume electricity – in a country that will struggle to meet its territorial electricity needs on a renewable basis.
Passive routes to thermal comfort should be emphasised instead. They should be a number one priority in all future housing – with interior temperatures remaining comfortable, without supplemental cooling, and despite rising temperatures outside.
Examples of passive cooling techniques include the use of long eaves and brise soleil, to reduce the amount of sunlight entering a building (solar gain). Windows should be oriented away from the sun.
Passive ventilation is important. It can be achieved by using through winds, cross-ventilation, or the stack effect – where cool air enters at the base of the building and is vented out the top. Wind towers, or wind catchers, are a beautiful example of this technology, which have been around for centuries in North and West Africa, and are now being widely used by contemporary architects. Natural ventilation can be supplemented mechanically, when necessary.
Meanwhile, the use of stone and earth indoors also contribute thermal mass, or thermal inertia, meaning that interiors heat more slowly during the day, and remain cool. Heavily insulated walls and ceilings can also help to retain heat outside.
The housing typology from Lagos, mentioned above, indicates no such features. Existing “modern” buildings such as these will need to be retrofitted to improve thermal comfort, for example, through the addition of brise soleil and external insulation.
All of these things are principles of bioclimatic design. Once again, local and historical knowledge goes a long way, and can be aided by modern engineering.[9]
Urban planning issues
Looking beyond individual buildings, neighbourhoods, cities, and all spaces of habitation should be actively designed to be humane and environmentally friendly. They should be aesthetically pleasing but varied. Neighbourhoods should have varied scales and structure, and be interspersed with plentiful green space.
Plants and water both serve to reduce ambient temperatures, and reduce the urban heat island effect. This is the tendency for urbanised areas to be warmer due to the presence of heat-absorbing urban materials instead of vegetation, and the heat-producing effects of domestic, retail, transport and industrial activities. Vegetation also reduces airborne pollution, supports wildlife, reduces flooding, and benefits people emotionally.
Settlements need to be made climate resilient for the future – necessitating climate-sensitive planning. Existing neighbourhoods will need to be upgraded (or in some cases moved); homes and neighbourhoods will need to be retrofitted – to protect inhabitants from increasingly severe temperatures, and from floods.
In Lagos, flood resiliency is already urgent, with significant and permanent inundation from the sea highly likely by 2050, according to the Intergovernmental Panel on Climate Change (IPCC). Open sewers and poor drainage are among the problems that need to be remedied.
Homes also need renewable sources of electricity, whether from a large-scale grids, or from local mini-grids (see part 16, below).
These are the principles that should be embraced when building Nigeria’s 66 million new homes between now and 2050, at a rate of 2.6 million new homes a year, and in retrofitting existing homes and neighbourhoods.
One obstacle to progress on building is Nigeria’s lack of “overarching strategy” or a unified policy framework around low-carbon buildings, according to the Cities Climate Finance Leadership Alliance (CCFLA). Energy use is regulated, but across different pieces of legislation. Local governments have insufficient funds to suitably train staff.[10]
The challenges are especially evident in Lagos, with its enormous housing backlog, continued rapid expansion in slum occupancy, and its coastal location.
Politicians and planners will need to find ways to rehouse slum populations in humane and well-provisioned urban neighbourhoods – with genuinely participatory and people-centered “slum upgrade” programmes. A wider and more holistic approach is required to the coastal environment of Lagos.
In my view, it looks very unlikely indeed that decent homes and neighbourhoods can simply be erected on the water.
Kunlé Adéyẹmí, the architect cited in the linked post, Nigeria: meeting the need for housing, won the prestigious Silver Lion prize at the 2016 Venice Biennale of Architecture for his Floating School in Makòko, “The Venice of Slums”. An admirable small-scale endeavour in many respects, but “by the time it received this honour,” writes Adéwálé Májà-Pearce, “the school had already been abandoned due to signs of instability, and was shortly destroyed by a heavy storm.”
A first step, with regard to the wetlands, is that dredging for new developments should be curtailed, if it impacts negatively on the surrounding hydrology and land-use.
Meanwhile, under normal circumstances, notes Májà-Pearce, the wetlands might themselves have helped, “mitigate the effects of global warming, by controlling shoreline erosion, preventing flooding, recharging underground water, and nurturing biodiversity – except that they are now, according to experts, ‘at risk of extinction,’ and this at the very moment when sea levels are expected to rise.”
Urban life needs forms of political economy, and forms of urban planning, based on the delivery of real needs – not a speculative economy built atop an extractive one.
Urban life also needs nature-based planning.
In the case of Lagos, this should encompass the recovery and regrowth of mangroves and other aquatic ecosystems – perhaps deployed in the context of a “sponge city” system of water-management infrastructures.[11]
Májà-Pearce writes that:
first-time visitors to Lagos will be struck by how generally denuded it is of vegetation, as if covering everything in concrete were necessary to hold back the ever-threatening wilderness.
However, between 2010 and 2020, the Lagos State government ran a rare, seemingly good and successful, environmental intervention: a mass tree-planting programme, under which 9.6 million trees were planted. Májà-Pearce notes that:
(s]ince trees trap significant amounts of water, they can be used to clear storm-water runoff, which is reduced by one million gallons for every 1,000 trees.
That could be the model for further, more extensive interventions in greening, rewilding, and natural flood defence.
Two “welcome bulwarks against further degradation” in Lagos, writes Májà-Pearce, are the 20-hectare Lekki Urban Forestry and Animal Shelter, a private venture by the environmentalist Desmond Majekodunmi, and the much larger Lekki Conservation Centre, “which promotes sustainable development and nature conservation, and is home to many endangered species.”
Yet these are far from enough: “relatively small-scale private ventures”.
To fund construction and environmental restoration, Nigeria should aim to finance many of the costs on its own account. (See part 2 of the pamphlet, Making Homes and Energy Transition in Nigeria.)
For that purpose, plant-based and earth-based materials are ideal. They can be sourced locally, or manufactured into prefabricated units – with the whole process taking place within Nigeria.
🔥 See also Making Homes and Energy Transition in Nigeria, by Tom Ackers (a free, downloadable PDF), and linked posts: Nigeria: meeting the need for housing and Nigeria: bringing energy to homes.
Notes
[1] For a general perspective on decarbonising embodied emissions, see Decarbonising the Built Environment: a Global Overview, part 8.
[2] High-tech alternatives to concrete include cementless concretes like Earth Friendly Concrete, and biogenic cements like Biocement. The manufacturers of Earth Friendly Concrete advertise that it has up to 70% less embodied carbon than regular concrete made with traditional cement. Housebuilding in Nigeria would be a prime candidate for such materials.
[3] Nigeria is a member of the International Bamboo and Rattan Organization (INBAR)
[4] For more details, see footnote 5 in Part 8 of Decarbonising the Built Environment: a Global Overview.
[5] Over its subsequent lifetime of use within a built structure, hempcrete (like cement) additionally absorbs CO2 from the atmosphere through the slow process of “recarbonation”. This (unlike with cement) makes hempcrete carbon negative over its whole lifecycle.
[6] This is notwithstanding Nigeria’s participation in the Great Green Wall initiative (see part 1, above).
[7] Compressed mud blocks can be stabilised using cement, and this makes them stronger and more resilient to water. The proportion of cement can vary. However, in order for the blocks to have comparable strength to concrete blocks, the cement content will tend to be roughly the same as what it is in concrete – meaning that the main emissions advantage of using mud disappears.
[8] The London building nevertheless used some concrete in the rest of the structure. However, the architects note that: “The lesson we learnt – after the concrete had been completed across the basement and upper floor slabs (on temporary props) over 12 months – is that we could have used CLT instead and cut around 8 months from the programme. Lower CO2 and, of course, it would have been cheaper too.”
[9] Just one recent small-scale building that uses principles such as these in Sub-Saharan Africa is a “maternity waiting village” in Malawi.
[10] The CCFLA adds that there is presently (2023), “early-stage activity on energy efficiency and embodied carbon building codes through the BEEC [the 2017 National Building Energy Efficiency Code], but states and LGAs have limited related regulatory frameworks or policies in place.”
[11] For more on “sponge cities”, see here.
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