More than half of the world’s 7.8 billion people reside in metropolitan areas. By the year 2050, an added 2.5 billion will be residing there. As that number continues to escalate, the question is: How do we accommodate everyone?

It is the task of city developers and urban planners to decipher how to construct or adapt urban environments to facilitate the needs of this growing populace. Some believe that more skyscrapers are the answer.

Yet this type of structure might not be the answer when it comes to reducing carbon?

One recent study found that densely constructed, low-rise environments are more space and carbon efficient, while high-rise buildings have a more extensive carbon impact.

The study reviewed the whole-life cycle of carbon emissions – both operational and “embodied” carbon – of buildings and urban environments. Operational carbon is generated while a building is being used. Embodied carbon is the concealed carbon processed during the extraction, production, transport and manufacture of raw materials utilised to build a building, as well as any produced during maintenance, refurbishment, demolition or replacement.

This aspect is frequently ignored, particularly in building design, where operational efficiency is valuable. The cause of reducing carbon at the design is gaining popularity with prominent international organisations like the World Green Building Council. But the issue is not legislated, but must be if we plan to attain 2050 emissions targets.

At a global level, the building sector is responsible for a substantial effect on the environment, as is evident from the graph below. The most significant contribution emanates from its consumption of energy and resources, which all comes down to the design stage – the stage of the process that no one is regarding.

Now that new buildings must be more energy efficient and the energy grid is being decarbonised, this concealed embodied energy varies from 11%-33% for projects like Passive House designs (a building standard that utilises non-mechanical heating and cooling design techniques to reduce energy use) to 74%-100% for near-zero energy builds (high performance buildings in which the low amount of energy needed emanates mostly from renewable sources).

Given the emphasis on reducing the energy impact of day-to-day operations, the proportional share of embodied energy consumption has been escalated. So as energy demand lowers when the building is being used, the materials and activities needed to construct it initially produce more impacts during the building’s life. Low and near-zero energy buildings are created by enhancing insulation and utilising more materials and technologies, which greatly enhances the hidden energy impact and carbon cost.

Shifting to a smaller scale, the embodied carbon share across building materials shows that minerals have the most sizable proportion by far, at 45%. The graph displays the breakdown of materials, where concrete dominates in terms of hidden carbon generation. Many skyscrapers are culled from concrete. So materials do matter—as do the manner in which we use them.

Research findings further show that high-density low-rise cities, like Paris, are more ecofriendly than high-density high-rise cities, like New York. Examining the fixed population scenarios, when shifting from a high-density low-rise to a high-density high-rise urban environment, the median increase in whole life-cycle carbon emissions is 142%.

And according to the fixed population size, building high-density low-rise provides a saving of 365 tonnes of CO₂ equivalent per person in comparison with high-density high-rise.

Urban planners must adapt and incorporate this new understanding into their designs, to make every city comparable to Paris—always a worthy goal!


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