**1. Introduction**

Sustainable Housing is a significant challenge of contemporary societies worldwide, addressed explicitly by the Sustainable Development Goals 1, 10 and 11 of the United Nation's Agenda 2030 [1]. By taking the triangle model of sustainability as a reference, the economic sustainability of housing rests upon the idea to push back a dominant profit-making strategy of capital accumulation and claiming a social infrastructure approach of housing instead. Ecological sustainability deals with eco-sensitive products and property-protecting housing construction without losing the practical needs of availability and affordability of income-poor households. While ecological sustainability is considered here rather implicitly, the contribution focuses on the conflicting interlinkages between the social sustainability of housing and the growing meaning of economic housing commodification.

Housing in its social dimension does not only provide a place for individual shelter and privacy that help humans survive physically. Moreover, it offers opportunities for community engagement and social inclusion. The neighborhood represents a significant institution to embed residents in social networks, enabling social capital creation such as trust, solidarity, and mutual support. From a theoretical perspective, the paper primarily though not exclusively refers to Bourdieu's concept of social capital and Rosanvallon's relational equity approach, with its ingredients of 'singularity', 'reciprocity' and 'community'.

However, the mentioned social functions of housing are challenged by a significant transformation and pluralization of lifestyles, labor conditions, family structures, and cultural aspirations of living, affecting sustainable housing policies. Housing has become more flexible, fragmented, multi-located and biographically dependent. More single (parent) households of younger and older people ask for social co-housing and intergenerational living solutions. Increasing housing prices are a big problem for low- and middle-income households, and the current COVID-19 pandemic crisis contributes to a massive relocation of functions to the home (working, consumption, schooling, and leisure). These multiple and conflicting housing functions induce a search for tailored political solutions to socially sustainable housing.

The paper delineates the outlined challenges by, firstly, discussing the numerous and different housing and neighborhood functions of contemporary modern societies. This section is meant to be a plea for considering the social functions of housing primarily. Secondly, a political and philosophical justification for this plea is presented, with reference to the theories of social capital and relational equity. Social functions of housing will, thirdly, be confronted with neoliberal economic housing functions to argue for political interventions that encourage social sustainability of housing. Several political measures will then be presented, which deemed suitable and necessary in this regard. Examples from European countries and cities are used to illustrate and elucidate the arguments raised throughout the contribution.
