*1.1. Research Background*

The problem of housing shortages is a major issue that has spread globally as urbanization has accelerated since the Industrial Revolution. Over time, this issue has changed to encompass many aspects. In the 1980s, the housing problems in the major cities of Germany, which is now considered to be a developed country, were discussed [1]. Even during this period, the lack of social housing and the imbalance in housing supply due to disparities in poverty and wealth were seen as problems. These characteristics have also been cited as common issues in developing countries, which have urbanized in recent years due to population growth. Several studies have been undertaken in India related to the problem of housing shortages. In Delhi, Abhay [2], while presenting the number of houses built in the recent decade (2001–2011), pointed out that, although the housing supply is stimulated by the housing shortage problem, low-quality housing is widespread. Kumar [3] pointed out that the large number of obsolescent houses is a fundamental problem that leads to housing shortages. He suggested that important measures in solving the housing shortage problem are improving the quality of housing through taxation or incentive polices for

**Citation:** Maddah, R.; Song, J.; Deguchi, A. Diversification of Villa-Type Neighborhoods and Its Impact on Housing Shortages in a Growing Saudi Arabian City: A Case Study of Jeddah. *Sustainability* **2022**, *14*, 7716. https://doi.org/10.3390/ su14137716

Academic Editors: Lucia Della Spina, Maria Rosa Valluzzi, Paola Pellegrini, Antonia Russo, Angela Viglianisi and Pierfrancesco De Paola

Received: 29 April 2022 Accepted: 15 June 2022 Published: 24 June 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

vacant houses, and making these houses usable and selling them. That is, although the supply of housing is important, it should be incorporated with the supply of housing to ensure peoples' quality of life.

In recent years, the problem of housing shortages in developed countries having relatively high urbanization has occurred at the regional level, rather than in entire countries, due to land prices and housing construction costs. The relatively high cost of housing is a major issue in Silicon Valley, USA, and Gabbe [4] examined whether administrative re-zoning planning would be effective. Tian [5] also summarized the relationship between land supply and land prices for four Chinese mega-cities, and pointed out that, even if rental housing is supplied, it does not contribute to addressing the housing shortage problem due to urban land monopolies. Thus, the circumstances regarding housing shortages differ from period to period and from country to country, and solutions must be considered in accordance with these differences.

A major difference regarding the housing supply in Jeddah is that the city has an Islamic culture. Sulf [6] proposed design requirements for housing in Saudi Arabia consistent with Islamic culture, in response to the worsening housing shortage due to population growth, in addition to low-cost housing for middle- and low-income people. Regarding housing development in Jeddah, it is necessary to closely examine how to solve the housing shortage problem associated with rapid population growth in terms of the formation of neighborhoods centered on mosques.

Hegazy [7] also evaluated urban development in Jeddah in terms of sustainable urban management. He criticized Jeddah's lack of planning tools for managing the total urban planning system and controlling illegal development, and emphasized a more integrated development management system. In this regard, it is deemed timely and appropriate to address the housing supply issue based on Jeddah's housing planning tool, the Procedure Manual for the Preparation of Residential Land Subdivision (PMPRLS). Mulliner [8] noted that Saudi Arabia is suffering from a housing shortage, and highlighted the gap between consumers' preferences and practitioners' preferences in the movement toward providing large quantities of housing on a shorter-term basis. This indicates the importance of diversity in housing attributes. Therefore, it is necessary to evaluate whether housing developed according to the PMPRLS in Jeddah would ensure a diversification of housing attributes.
