15 In per capita terms, the list includes many MICs (Argentina, Colombia, the Arab Republic of Egypt, Indonesia, Mexico, and T ̈urkiye). Focusing on total volume, the list is dominated by populated developing economies with large per capita needs (India, Indonesia, Mexico, T ̈urkiye, the Philippines, Bangladesh, Pakistan, Colombia, Brazil, and Egypt). LICs are absent from the lists as there is less variation in volumes per capita at low income levels than at intermediary income levels.

Only considering developing economies below the line, the mean per capita gap is 24 m<sup>3</sup> in Africa, 47 m<sup>3</sup> in Asia, and 65 m<sup>3</sup> in LAC (respectively 5 m<sup>2</sup> , 9 m<sup>2</sup> , and 13 m<sup>2</sup> assuming a housing share of 50% and a 2.5. m ceiling height). However, for total volume needs, we get 15 billion, 125 billion, and 36 billion m<sup>3</sup> , respectively. More generally, developing Asian economies account for _∼_ 60% of the world gap (vs. 17% for developing LAC and 7% for Africa), with South Asia explaining two-thirds of developing Asia’s gap, and India contributing to _∼_ 70% of South Asia’s gap. India might need to build 54 billion m<sup>3</sup> , more than half of its current stock. For Indonesia, it is 20 billion m<sup>3</sup> , one-third of its current stock. Globally, bridging the gap would increase stocks by _∼_ 14%.

However, other factors could affect the economic, social, and environmental “optimality” of construction patterns. Bridging the gap could have dramatic effects on the environment, given the building sector accounts for 39% of carbon emissions worldwide (UNEP, 2022). Meeting the estimated global needs would increase global carbon emissions by _∼_ 5%, implying trade-offs between promoting housing affordability and ensuring livability/sustainability.

# **4.3. Quantifying Future Global Construction Needs**

**4.3.1. Forecast until 2025**

The forecast of future, growth-driven construction needs is a crucial tool in view of a fasturbanizing world and unaffordable cities (UN Habitat, 2020; The World Bank, 2023b). With estimates of the future population and income of a country, we can quantify by how much the country’s volume must increase to match global construction trends. From the estimated quadratic fit in Figure 4, we obtain coefficients _α_ (2,209***), _β_ (-580***) and _γ_ (39***) in eq. (6): _V olume/Population_ = _α_ + _β ∗ log_ ( _GDP/Population_ ) + _γ ∗_ ( _log_ ( _GDP/Population_ ))<sup>2</sup> (6) Using data from the World Bank (2019), we obtained the predicted real GDP growth rate of each country in 2019-2022. We consider countries from the viewpoint of 2019, thus ignoring the unrelated economic effects of the COVID-19 pandemic. Using the average annual growth rates in 2019-2022, we estimate each country’s GDP in 2025. From the United Nations (2019), we obtained each country’s predicted population in 2025 (ignoring COVID-19 mortality).<sup>5</sup> Equation (6) is used to estimate how Volume/Population may need to change as

> 5The COVID-19 pandemic could reduce construction needs by increasing mortality and depressing economic growth. However, the remote work revolution has dramatically increased housing demand.