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DASBE is funded by the Higher Education Authority's HCI Pillar 3, a government programme designed to meet priority skills needs, by increasing collaboration between higher education and enterprise with a focus on innovations in teaching and learning.

As of 2007, most humans live in cities. Though this is a relatively recent trend, many of our settlements contain street, block and building patterns that have developed over centuries.

These patterns – which collectively make up what we call 'urban form' – are far from a neutral backdrop: they influence who lives where, what businesses find footholds in which locations, and what makes some areas more diverse than others.

'Bottom-up' and 'top-down' are terms which are often used to pin down the two ends of the vast range of urban form. Bottom-up refers to neighbourhoods which develop naturally and gradually, without a strict master plan guiding their development.

Top-down, on the other hand, refers to urban form that is designed by singular authors, with much tighter controls over, and ideals around, how it should develop over time.

If we look at bottom-up neighbourhoods from a bird's eye view, we tend to see a variety of block sizes, street widths and public spaces, and often maze-like street patterns.

Top-down areas, by comparison, tend to be less varied, with clear evidence of their authors' vision and values regarding urban geometry and the nature of public space – grid systems and sweeping boulevards abound. Many cities have bottom-up and top-down neighbourhoods existing side by side, legacies of different political and socioeconomic eras. 

Cities also reflect the values of time, place, and history. Today there are extensive discussions of bottom-up development and how it fosters communities and neighbourhood identity, while the lasting imprints of top-down regimes are still clearly visible in contemporary cities around the world.

For centuries, architects, planners and philosophers have suggested that bottom-up areas of cities tend to be more inclusive than top-down ones, supporting a wider range of economic classes. However, decisively proving such a theory has proved challenging.

How the built world shapes demographics

The link between urban form, class and economic diversity follows two lines of thought. The first is an extension of ecology. In natural habitats that have developed slowly over time – through bottom-up processes – we tend to observe a wide range of species. However, in planned habitats – built much more rapidly in a top-down manner – this kind of richness is often markedly absent. Slow growth tends to produce more intricacy and diversity, and this idea is often extended to theories of urban form.

The second line of thought is economic. Consider the diversity of public spaces in bottom-up districts – different sized streets, alleyways, squares, parks, courtyards, and so on. This variety of public spaces creates different qualities of light and air, as well as a wide range of favourable and less favourable conditions. 

A more varied real estate market should, in theory, emerge as a byproduct of this diversity: a dark, poorly ventilated apartment is cheaper than a bright, airy one; a dwelling overlooking a pleasant square is more marketable than one next to a narrow alley. These varied spaces can host a varied population – a range of different ages, household sizes and income levels, all living cheek to jowl alongside one another.

In a top-down neighbourhood such variety is often absent, as buildings, streets, and public spaces tend to be more uniform. This homogeneity should, in theory, limit population diversity.

Examples from Madrid and Barcelona

In late 2021, we conducted research into the relationship between urban form and housing. We looked at two districts in Barcelona and two in Madrid, with one bottom-up and one top-down in each city, homing in on areas with similar average real estate values. The neighbourhoods examined were Bellas Vistas and Palos de la Frontera in Madrid, and Vila de Gracia and Nova Esquerra de l'Eixample in Barcelona.

Curiously, our research both confirmed and subverted the presumed theoretical link between urban form and housing stock, and the presumed supremacy of bottom-up over the top-down areas in fostering economic diversity. 

Our main finding was that the bottom-up districts we looked at had, overall, more small-scale apartments. The reason is simple: they had more small-scale buildings, built on small-scale plots. Once divided into apartments, this produces small apartments – homes in the bottom-up areas were 10% to 23.1% smaller than their top-down counterparts. This also made their real estate markets for small homes more competitive, and therefore more affordable.

However, our study showed there is nothing inherently magical about bottom-up areas. Their more intricate housing stock has little to do with the layout of streets and blocks, and a lot to do with how that land is built upon.

Plot size appears to be the deciding factor: the districts with greater numbers of small buildings built on small plots supported a denser and more affordable housing stock, regardless of whether they were top-down or bottom-up. 

Older bottom-up areas seem to naturally lend themselves to having more small-scale plots. This is likely due to the incremental development of these areas, and the complex land ownership patterns that developed as a result. However, there is no reason why a top-down area cannot be designed to replicate these characteristics.

Implications for the housing crisis

Governments seeking to rein in housing markets can take action to encourage development on a smaller scale. One rather blunt, though potentially fruitful, method is limiting ownership of urban land by a single individual or corporation, or limiting the footprint and size of non-public buildings that can be built within a city. Although it applies to agricultural land, the limitation of private ownership to 50 acres per person in Sri Lanka is a useful case study here.

Even in countries like the United States, where property rights are wielded in objection to such arguments, there is a longstanding debate on the fundamental necessity of land ownership limitations in maintaining a functioning capitalist system.

As housing crises rage across the world, many cities are in dire pursuit of a more affordable, more varied, and more inclusive housing stock. It is increasingly clear that urban policies aiming to achieve this solely by addressing real estate development are falling woefully short of their aims on a global scale.

What our research indicates is that deeper, more structural approaches may be worth considering – approaches that not only address the physical form of the city, but also the ownership patterns that underpin it. Approaching urban land ownership and architecture on a smaller scale may hold potential that is not yet being used in full. 

Authors: Cem S. Kayatekin is assistant professor of architecture and urbanism at the IE School of Architecture and Design at IE University, Lorenzo Uribe Sanmiguel is a junior architect at OMA at IE University. This article was originally published by The Conversation.

Aside from water, concrete is the most-used material in the world, with about 14 billion cubic metres being used every year, writes Professor Jamie Goggins, University of Galway. Of that, 40% of that is used to build places for people to live.

If you were to pour that amount of concrete to make a paving slab ten centimetres thick, it would cover all of England and about half of Wales. In the US, the same amount would cover the state of New York.

But concrete production releases carbon dioxide (CO₂), one of the greenhouse gases that drives climate change. About 90% of emissions associated with concrete come from the production of Portland cement – this fine grey powder, the part that binds concrete ingredients together, was named after its resemblence to stone from the Isle of Portland, Dorset. Portland cement accounts for 7%-8% of the world’s direct CO₂ emissions. 

A new first-ot-its-kind green cement plant in Redding, California, has 70% lower emissions than conventional cement production. Image: Fortera, CC BY-ND.

Production of a more sustainable and cost-effective low-carbon cement, often nicknamed 'green' cement, is scaling up. A new plant next to an existing cement plant in Redding, California, will produce about 15,000 tonnes of low-carbon cement every year. This could be used to make about 50,000 cubic metres of concrete, which is less than 0.0004% of the world’s concrete production. 

At Redding, materials technology company Fortera turns CO₂ captured during conventional cement production into ready-to-use green cement, a form of calcium carbonate. This could reduce carbon emissions of cement by 70% on a tonne-for-tonne basis, according to Fortera.

A concrete issue

People have been using concrete for more than 2,000 years, by blending gravel, sand, cement, water and, sometimes, synthetic chemicals. It is used to create everything from paths and bridges to buildings and pipes.

Currently, the EU uses more than two tonnes of concrete per person per year – 325kg of that is cement. That is equivalent to the amount of food the average European person eats in five months.

Cement production is an energy-intensive process and the greenhouse gas emissions are hard to cut. When limestone is heated in a kiln, often fuelled by coal, nearly half that limestone is lost as CO₂ emissions.

This happens because limestone (calcium carbonate) breaks down in heat to form clinker, a mix of calcium oxide and CO₂. For every tonne of ordinary Portland cement made, 0.6-0.9 tonnes of CO₂ are released into the atmosphere.

So many industries rely on this material. The main challenge facing the cement industry is reducing CO₂ emissions at the same time as meeting global demand.

So as well as developing new technologies, low-carbon cement production must be established on a global scale to meet infrastructural needs required of economically developing nations.

Low-carbon alternatives

Other ways to reduce the carbon footprint of concrete include using fly ash (a byproduct from burning coal in power plants) or slag (a byproduct from steel production) to partially replace Portland cement.

However, sources of these materials will reduce as other industries decarbonise. Over time, less iron ore will be used to produce steel as more steel is produced from recycling existing steel, so there will be less available slag.

Current strategies for decarbonising cement and concrete rely heavily on using carbon capture and storage technology to capture unavoidable process emissions from cement plants.

So low-carbon cement production does not have to involve replacing every cement production plant in operation. Low-carbon cement facilities can be retrofitted to capture CO₂ emissions released from manufacturing conventional cement. Plants can also use that captured CO₂ within the cement that they are producing or as a product for the food and chemical industries.

In Norway, Heidelberg Materials are building an industrial-scale carbon capture and storage plant at a cement facility that could capture and store an estimated 400,000 tonnes of CO₂ per year – that is half the existing plant’s emissions.

However, this technology has a high investment cost for cement producers. Captured CO₂ can be stored underground, but this requires specific geological characteristics that aren’t guaranteed at cement production sites.

Greenhouse gas emissions in the cement sector are regulated by the EU’s emissions trading system. This was established to make polluters pay for their greenhouse gas emissions, reduce emissions and generate revenues to finance the green transition.

This legislation has not significantly reduced carbon emissions in the cement sector over the past decade, according to the International Energy Agency, mainly due to free emissions allowances being granted to cement manufacturers.

Despite sustained healthy profits in the cement industry, there has not been enough investment in the widespread uptake of cleaner technologies and the sustainable use of materials. Greater financial incentives could help whereby companies have to pay for emissions associated with the production of cement. 

Fortera is the only company directly capturing carbon emissions from cement production to make a pure low-carbon cement binder like this. Image: Fortera, CC BY-ND.

As a design engineer, I appreciate that material choice and good design play a significant role in the sustainability credentials of construction. Before low-carbon cement technology becomes more widespread, engineers, designers and builders can use construction materials more efficiently and choose products with lower embodied carbon – that is carbon emissions released during the life cycle of building materials, from extraction through to disposal.

This approach could easily save 20% in embodied emissions associated with new building design.

Some governments could move towards only permitting the use of low-carbon cement. In Ireland, the Climate Action Plan 2024 requires that low-carbon construction methods and low-carbon cement are specified where possible for government-procured or government-supported construction projects.

Could all cement in the future be low-carbon or 'green'? How 'low-carbon' is defined will play a very important part in how this is translated into practice in the industry.

Retrofitting technology to large-scale existing cement production plants will prove that it is technically possible to produce low-carbon cement efficiently at scale. With the right incentives in place by governments and the construction sector, almost all cement produced around the world could be low-carbon. 

Author: Jamie Goggins, professor of civil engineering, College of Science and Engineering, University of Galway. This article first appeared in The Conversation.

Research by the Trinity research group STONEBUILT Ireland, based in Geology in the School of Natural Sciences and led by Professor Patrick Wyse Jackson and Dr Louise Caulfield, in collaboration with colleagues at Valentia Slate Company Ltd and Carrig Conservation Consultants, has resulted in this global designation.

The work has just been published in the Irish Journal of Earth Sciences and can be read open access on the journal website. 

Excellence in construction and domestic use

Valentia slate has all of the qualities needed for excellence in construction and domestic use. It is extracted underground on Valentia Island in the same facility that was opened by Peter Fitzgerald, the Knight of Kerry, in 1816.

The company operates a zero-waste policy in extracting slate for a wide variety of purposes including flooring, roofing slates, kitchen countertops and funerary headstones.

Worldwide, buildings are major emitters of greenhouse gases. Natural stone is a very low-carbon building material and Valentia slate is delighted to be part of a modern trend to use more natural stone and timber in architecture, simply because this approach is better for the climate.

Prof Wyse Jackson said: “Valentia slate is a unique stone type that only occurs in Co Kerry. Its characteristics allowed it to be split into roofing slates but also large slabs and it was utilised for a wide variety of domestic and commercial applications.

"Among the more unusual uses were for headstones, garden benches, billiard tables, water tanks, and walling for bonded warehouses. The research project STONEBUILT Ireland, funded by the Geological Survey Ireland and Office of Public Works, enabled research on this important sustainable commodity.”

Sustainable construction

Aidan Forde, a geologist, is owner of Valentia Slate Company Ltd. He said: “This recognition is also of the expert and hard-working staff of Valentia slate who have made the company what it is today. This award is recognition, not only of their own efforts in keeping Valentia slate available for use in sustainable construction, but also the work of the many generations of south Kerry people who worked at the quarry.”

Peter Cox, a material scientist, is founder and managing director of Carrig Conservation International Limited and has decades of experience in the Conservation of historic Buildings across the world. He said: “Valentia slate is one of the purest and finest products I have come across in my 40 years working in this sector.

"The material has been used on many very important international buildings; it is vitally important that historic materials such as Valentia slate are available for conservation and repair of these buildings. It is an added bonus that slate is now available from an Irish source to reduce carbon in our modern construction market.”

1. HEATCHECK is a platform developed through funding from the Sustainable Energy Association of Ireland (SEAI), which uses sensors to monitor CO₂, humidity and temperature in about 100 LDA developed homes to understand building performance and behaviour when occupied. The data will help to inform future building standards to ensure healthy, low energy homes.
2. INDICATE is a Carbon Life Cycle Assessment Procedure offering a standardised approach to calculating the carbon associated with the production, construction, operation and end-of-life stages of a building life cycle. It benchmarks the carbon associated with different building types in Ireland (residential, offices, hospitals etc) which the LDA uses to understand and minimise the carbon impact of their developments and support the development of policy recommendations.
3. The LDA is partnering with the Irish Green Building Council (IGBC) on a project to mainstream biodiversity in the construction sector by developing high-quality, practical case studies on how to protect and enhance biodiversity in the most common building typologies and infrastructure found in Irish towns and cities. It is supported through the first Construct Innovate Seed Fund call from 2023.

The LDA is a member of the IGBC’s Community of Practice on Biodiversity and the Built Environment, which Minister of State for Heritage and Electoral Reform Malcom Noonan T.D. launched in May 2023 to share and promote discussion and what is working well in Biodiversity and the Built Environment.