million housing units will have to be added to provide adequate housing to the growing population by 2030. Regarding the deficit at the dimension level, we estimate that at least 603 million HHs (close to 2.8 billion people) in emerging economies lack access to at least one of the seven dimensions of adequate housing. Our prediction indicates that not only HHs residing in slums are lacking access to adequate housing, as the UN estimation suggests (UNSD 2019). Instead, the housing deficit is much more wide-ranging, extending to HHs in formal settlements.

In constructing the AHI, we present a transparent framework for harmonizing seven dimensions of housing adequacy recorded in countries’ most recent HH surveys. To the best of our knowledge, this is the first broad, cross-country study applying a uniform methodological framework on housing adequacy and related housing deficit estimations. This cross-country assessment of existing adequate housing deficits will facilitate consistent projections of how the adequate housing deficit will rise within the context of urbanization and population growth.

In our analysis, we highlight important within-country variation in housing needs across different segments of the population. Further, in separately estimating the current housing deficit and the forward-looking deficit likely to manifest over the next decade, we draw a fundamental distinction between the stock and flow housing deficits. This differentiation is often not appropriately stated in existing estimations of housing deficits. Instead, stock and flow deficits are frequently used interchangeably, partly because only one type of estimation is available for the country.

The remainder of this paper proceeds as follows: in the next section, we briefly discuss how our approach relates to existing literature on estimating housing deficits and outline how literature assesses the relationship of housing adequacy and socio-economic outcomes. We discuss how recent estimations of housing deficit largely abstain from differentiating between the stock deficit of currently inadequate housing units and the flow deficit – often referred to as the quantitative housing deficit denoting how many additional housing units will have to be built. Next, we outline our methodology in constructing the _AHI,_ which is the basis for the housing stock deficit estimation and discuss the various data sources we use. Thereafter, we present results of the aggregate _AHI_ for 64 countries and its respective adequacy components. We discuss within-country adequacy deficits, segment the population into income deciles, and disaggregate the _AHI_ on other dimensions such as location, education, gender, or occupation. Next, based on the _AHI_ and other demographic projections, we estimate the current housing stock deficit as well as the flow deficit of housing likely to arise by 2030 with business-as-usual policies and private sector practices. Finally, we offer a brief conclusion outlining how the _AHI_ can help identifying adequacy housing needs of different segments of the population so that housing interventions can be more targeted, appropriately designed, and implemented. We conclude by outlining avenues for future research.