Introduction

Spain has long been an attractive case study in housing and urban research. Unique and traditional aspects, such as its unbalanced tenure pattern and its poorly developed social housing sector, have attracted both national and international researchers, undeterred by the country's social diversity and spatial heterogeneity (Allen et al, 2004; Bonvalet et al, 2009; Arestis et al, 2009, among others). This complexity has been further exacerbated by the effects of the recent economic crisis, manifested locally by the rising rates of unemployment affecting many people, particularly the young, threatening to push them below the poverty threshold; and by the pressing need to preserve the environment for future generations, a priority in the design of many public intervention strategies. The impact of both developments at the local level, together with the ability of local bodies to respond to their potential impact on the country's socio-spatial fabric, highlight the essential role played by the housing system.

Housing is a unique, immovable good, hence the importance of the spatial and social context in which it is framed. The dynamics of the city, and of the built environment in general, respond largely to a country's internal housing demands, for example the evolution in its demand and supply behaviour and public policy initiatives. A city's historical development, its spatial location, its built urban environment and the demographic makeup of its residents are among the factors that influence and determine its resilience. These elements provide mechanisms that can mediate in the process of finding solutions to the problems generated in cities as a result of globalisation (Marcuse and van Kempen, 2000).

The four pillars of sustainable development (that is, environmental protection, economic growth, social equality and effective governance) require long-term strategies that are often difficult to implement in practice (Pareja-Eastaway and Stoa, 2004). In the Spanish case, the process of accommodating urban environments to new global demands has been accompanied by large migratory flows, and by a boom in the real estate market followed by a crisis that has struck at the very root of that sector. In order to alleviate the effects of this process, the public authorities face new challenges and pressures within the existing housing system as they seek to redefine their approach to public initiatives in housing policy. Now more than ever, regeneration and renewal policies constitute a key role in housing provision, especially for certain vulnerable groups.