Uncovering Social Sustainability in Housing Systems through the Lens of Institutional Capital: A Study of Two Housing Alliances in Vienna, Austria

: This paper analyzes social sustainability in the context of urban housing through the lens of institutional capital. It examines how civil society housing actors co-construct bottom-linked governance arrangements by interacting endogenously with peers and exogenously with institutional actors, such as public housing agencies and elected ofﬁcials, in order to steer, as housing alliances, socially sustainable residential developments. The paper thus offers an answer to the following two research questions: (1) What are internal governance features that characterize such civil society housing alliances? (2) What are their strategies of interaction with institutional actors in order to promote social sustainability and thus counter exclusionary patterns in urban housing systems? Empirical evidences are drawn from two civil society housing alliances in Austria, ‘BAWO’ (a national alliance of homelessness NGOs) and the ‘Initiative Collaborative Building & Living’. During three research stays in Vienna between 2014 and 2020, data was collected through semi-structured interviews and focus groups with leaders and members of housing alliances, interviews with key institutional stakeholders and web research. By reﬂecting on the institutional and relational character of the two housing alliances and digging out their potential and limitations in promoting different elements of social sustainability, our paper concludes that social sustainability in housing systems can be realized when it is set as a societal ambition sufﬁciently politicized by major parties involved in housing systems (housing alliances, governmental authorities of all ideological backgrounds, large non-proﬁt housing developers) that collectively guarantee housing affordability and socio-spatial equity for all.


Introduction
Recent research in sustainable development scholarship has focused on the systemic study, conceptualization and definition of social sustainability-it is one of the three major pillars of sustainable development that has hitherto remained insufficiently and/or inadequately scrutinized [1][2][3][4]. Shirazi and Keivani [4], as well as Bostrom [1], present an overview of the wide range of approaches in the analysis of social sustainability covering various (often overlapping) substantive and procedural aspects of socially sustainable societies. These include the satisfaction of intra-and intergenerational human needs, social and community infrastructure, cultural development, equity and democracy, quality of governance and community empowerment. Bostrom [1] and Mehmood and Parra [3] have cast bolder light on the latent political potential of the framing of social sustainability. When understood from a predominantly functionalist perspective, social sustainability means the improvement of living conditions coupled with a consensual, techno-managerial governance of territorial development counting on quantitative evaluations of performance, which depoliticizes the concept [3]. However, when social sustainability is narrated as part of a broader participation process towards societal transformation, then the making of socially sustainable communities is underpinned and guided by democratic values of decision making, the co-production of goods and services and a deeper civic engagement and responsibility in visioning, planning for and maintaining social sustainability for all.
Social sustainability has also been explored specifically within the built environment context, covering physical and non-physical dimensions such as social and community cohesion, sense of community and belonging, residential stability, safety and security, active and reciprocal community organizations but also decent housing, accessibility to services, green spaces and public transport, sustainable urban design and walkable neighborhoods [2]. Other scholars [4,5] have investigated social sustainability more specifically in the housing sector, examining housing affordability, accessibility to the housing market and to public housing, adequate public funding on housing, social capital of non-profit housing actors for community development, social cohesion and inclusion in and through the management of collaborative housing and new housing governance configurations (stronger ties between residents, housing cooperatives, collaborative housing umbrellas and decision makers).
An emerging theme in the social sustainability scholarship is the importance of its procedural dimensions (participation and democratic governance) and the 'relational' content of the 'social'-namely, the multi-scalar and multi-level interactive explorations, collaborations and struggles by humans 'on the ground' (micro-scale of communities and neighborhoods) in their effort to meet the material and immaterial conditions for interand intra-generational equity [1,3,5,6]. According to Parra [6] (p. 146) "what is 'social' about sustainability is how societies organize taking in hand (or not) the ensemble of sustainability challenges needing and leading socio-political negotiations". Together with Frank Moulaert [7], Parra [8] argues that governance is the fundamental engine of sustainability, precisely because, when coupled with democratic values and practices, it opens questions such as who should be in charge of defining and satisfying human needs and innovating in governance across different and changing socio-spatial contexts? Thus, social sustainability refers to a societal project that encourages governance transformations for change towards inter-and intra-generational equity and calls for targeted institutional support and coherent policies to support novel governance configurations and a plurality of alternatives for human needs satisfaction.
Previous research on the social sustainability-housing nexus has stressed the essential role of housing cooperatives and their umbrella organizations in supporting residentled housing projects to be connected with institutional actors (such as public authorities, elected officials and public housing providers) through coordinated outreach and mediation [5]. However, the politico-institutional component of social sustainability, especially when applied in the urban/housing contexts, remains undertheorized and needs to be scrutinized in more depth. This paper addresses this gap by delving into the governance aspect of social sustainability analysis and connecting institutional capital to social sustainability and embedding it in housing systems. It examines social sustainability by casting light on politico-institutional fermentations that steer egalitarian housing governance and provision-in other words, promoting housing for all and by all. The paper provides an in-depth analysis of the politico-institutional tissue in which social sustainability is embedded and reinforces social sustainability with theories of bottom-linked governance and institutional capital. This analysis draws on civil society organizations that initiate and lead socially innovative initiatives by utilizing resources and their social capital in novel ways to satisfy human needs and by developing new forms of collaborations among each other and with public authorities. Particular modes of collaboration involve bottom-linked governance configurations [9,10], which turn out to reinforce democratic decision-making needed for the formation of housing and cities for all [11,12].
The ambition of this paper is, thus, to open the boundaries of knowledge on the nexus between social sustainability, institutional capital and bottom-linked governance. It does so by focusing on the collective building and institutional innovations (often bottomlinked modes of governance) of alliances of housing actors originating from civil society (homelessness service providers and collaborative housing initiatives) that aim to preserve and produce affordable housing for all. The paper studies how bottom-linked governance led by these alliances contributes to the formation of social sustainability in housing systems, especially in the midst or the aftermath of enduring multifaceted housing crises that undermine affordability and leave the old fashioned, top-down governance of housing systems in place. Nevertheless, we have seen a re-emergence of civil society housing alliances who aim to improve the policy culture (urban planning instruments, affordable housing policies) and the institutional actors (governmental and state authorities, social housing companies) that direct housing provision processes. Thus, housing alliances have become the custodians, renewers and implementers of the welfare state's political objective of achieving adequate housing as a basic human right.
Against this backdrop, the paper aims to explore the unique histories of two Austrian housing alliances and their advocacy strategies to productively interact with institutional actors in their effort to build up a collective force to advocate for housing for all. The paper thus offers an answer to the following two research questions: (1) What are internal governance features that characterize such civil society housing alliances? (2) What are their strategies of interaction with institutional actors in order to promote social sustainability and thus counter exclusionary patterns in urban housing systems?
The paper is structured as follows: Section 2 outlines the methods underlying this study. Section 3 introduces the key concepts underpinning the analysis of this paper (bottom-linked governance, institutional capital) leading to a predefinition of social sustainability in housing systems. Section 4 briefly presents the context of the Austrian/Viennese housing policy landscape and recent trends, followed by the empirical findings of the two Austrian civil society housing alliances. Section 5 provides a cross-case analysis and draws conclusions on the potential and limitations of housing alliances and their politico-institutional innovations in bolstering social sustainability in housing systems.

Methods
This paper is theoretically embedded in the scholarship of bottom-linked governance and institutional capital. The reflections stimulated by this work have deepened the methodological insights necessary to 'case-proof' the methodology of our research. More specifically, a preliminary understanding of the conditions within which housing alliances emerge, perform new political positions and opt for bottom-linked governance practices and the realization of social sustainability are sought in the work of social innovation scholars writing on bottom-linked governance [13][14][15][16][17][18][19][20][21][22] and institutional capital [11,21,[23][24][25]. This synthesis provides the basis of the analytical framework for case study work on the following two civil society housing alliances in Vienna (Austria): 'BAWO' (a national alliance of homelessness NGOs) and the 'Initiative Collaborative Building & Living' (an umbrella body for collaborative housing forms in Austria).
Empirically, the paper draws from the Viennese housing system, which is characterized by a 'social sustainability deficit' as it has traditionally accommodated the needs of medium-income citizens and paid insufficient attention to people seeking collective residential lifestyles and those customarily discriminated by housing markets (especially refugees and homeless people). The empirical research applies comparative case studies as this methodology appears suitable to reconstruct the genesis and configuration of housing alliances within a particular territorial and institutional context [26,27]. It also follows the tradition of longitudinal and process-orientated qualitative research with various types of data (e.g., from interviews, focus groups and secondary data) collected at different points in time between 2014 and 2020. An important element of such an approach is a narrative and temporal bracketing strategy to uncover significant periods of relationship building and actor collaborations in relation to housing alliances and their wider institutional environment [28]. Data collection was carried out by both authors during research stays in Vienna in 2014/15, 2018 and 2020. The following research methods were mobilized. First, semi-structured interviews were conducted with leaders and founding members of housing alliances-representing bottom-up social innovators. These interviews especially provided crucial information on the evolution of the civil society housing alliances, their intra-level (endogenous) interactions and inter-level (exogenous) interactions with institutional actors and related governance-building practices. Second, to overcome limitations related to one type of data collection and to cast light on the temporal dimension of social interactions in our two case studies (i.e., how social interactions unfold over time), we additionally carried out focus groups with representatives of different bottom-up socially innovative organizations connected to our case housing alliances at two different points during the study. Third, to contrast different perspectives on institutional capital building, we further conducted semi-structured interviews with key top-down receptive institutional stakeholders of our case housing alliances, such as representatives of a non-profit housing umbrella body and a municipal housing department. Finally, we complemented primary with secondary data collection from organizations' websites, documents, and policy/advocacy reports. Altogether, this triangulation strategy enhances the reliability and validity of the data [27,29].
Corresponding with the nature of our research aim and the richness of our gathered data, we employed interpretative qualitative data analysis [30]. In that analysis, we started with deductive coding informed by the bottom-linked governance and institutional capital literature and, in particular, by the earlier outlined components of both endogenous and exogenous institutional capital. Then, we inductively iterated and refined the codes and organized them to represent a chronology of endogenous and exogenous institutional capital evolution before constructing our final narrative. Table A1 in Appendix A provides a summary of key empirical data sources used for this paper and provides details on the longitudinal approach. Across the three phases, we carried out interviews and focus groups with the same and different respondents to ensure consistency and to be able to verify statements.

Uncovering the Conceptual Nexus between Bottom-Linked Governance and Institutional Capital in Housing Systems
Bottom-linked governance has emerged as a key concept in social innovation scholarship, particularly because of its 'positive' analytical, action-oriented, socio-political transformation potentialities [13][14][15][17][18][19]22]. It is understood as a novel and dynamic governance modality between top-down receptive institutional actors (e.g., public authorities, elected officials, large housing developers, charity groups and foundations) and bottom-up social innovators (e.g., non-profit/non-governmental organizations, community initiatives, social movements) aiming for the satisfaction of human needs, the co-construction of public policy and the formation of more democratic public institutions and participatory decisionmaking mechanisms. Thus, it breaks the dichotomy between 'top-down' and 'bottom-up' forms of governance through negotiation, co-learning and confrontation across members of multi-level and multi-organizational partnerships and coalitions. The latter, in turn, encourage reflexivity in governmental practice and institutions and the effectiveness of the design and implementation of public policies [13,[16][17][18]20,21].
Bottom-linked governance materializes through interactions between organizations within and across different institutional levels (see Figure 1). Intra-level governance comes into being through the horizontal interactions among social innovators (see dashed arrows on Level 1 in Figure 1) and the resulting development of endogenous institutional capital, which, for instance, becomes formalized as alliances or advocacy groups (see dashed circles on Level 1 in Figure 1). In intra-level governance, social innovators activate their social capital (reciprocity, trust, cooperation, collective visioning, shared leadership, community outreach, support of local civic networks, promotion of associational activity) to form horizontal interactions with peer social innovators and, in doing so, co-construct institu-tional capital essential for further reinforcing solidarity-inspired inter-level governance edifices [11,21]. Collective agents embodying endogenous institutional capital (such as alliances or advocacy groups in Figure 1) aim at developing and strengthening partnerships with institutional actors and advocate for governmental policy improvements that would benefit both their members and their target communities [11,23,31,32]. their social capital (reciprocity, trust, cooperation, collective visioning, shared leadership, community outreach, support of local civic networks, promotion of associational activity) to form horizontal interactions with peer social innovators and, in doing so, co-construct institutional capital essential for further reinforcing solidarity-inspired inter-level governance edifices [11,21]. Collective agents embodying endogenous institutional capital (such as alliances or advocacy groups in Figure 1) aim at developing and strengthening partnerships with institutional actors and advocate for governmental policy improvements that would benefit both their members and their target communities [11,23,31,32]. Inter-level governance is built up through inter-level (adversarial and non-adversarial) interactions (see solid arrows in Figure 1) between social innovators (and/or their allies) (on Level 1 in Figure 1) and public and private institutions (on Level 3 in Figure 1). These bottom-linked governance processes (see Level 2 in Figure 1) represent new opportunities for solidarity forms of governance and further produce exogenous institutional capital (see solid circles on Level 2 in Figure 1), which becomes formalized for instance as public participation forums (e.g., public hearings), human-centered Public-Private Partnerships (PPPs) or inter-institutional alliances (e.g., 'Housing for All' coalitions) [11]. Inter-level governance is built on social capital features (advocacy/lobbying, shared leadership) that constitute the exogenous governance structures of social innovators with the purpose of leveraging governmental, policy and financial support (policy changes, public subsidies, financial incentives, program experimentation) [11,21].
Both endogenous and exogenous institutional capital share three key components: shared knowledge resources, relational resources and mobilization capacity [23,25]. New forms of institutional capital are built up through exchanges of different forms of local knowledge and of analyses of socio-spatial phenomena, the formation of new and extended webs of relations between and across socio-political actors in territories, as well as the development and dissemination of new discourses leading the design and implementation of actions. Such fermentation of territorial institutional capacity generates public policies and funding distribution for territorial social sustainability, and also nurtures an improved quality of governance cultures and ways of 'relating' and collaborating (i.e., Inter-level governance is built up through inter-level (adversarial and non-adversarial) interactions (see solid arrows in Figure 1) between social innovators (and/or their allies) (on Level 1 in Figure 1) and public and private institutions (on Level 3 in Figure 1). These bottom-linked governance processes (see Level 2 in Figure 1) represent new opportunities for solidarity forms of governance and further produce exogenous institutional capital (see solid circles on Level 2 in Figure 1), which becomes formalized for instance as public participation forums (e.g., public hearings), human-centered Public-Private Partnerships (PPPs) or inter-institutional alliances (e.g., 'Housing for All' coalitions) [11]. Inter-level governance is built on social capital features (advocacy/lobbying, shared leadership) that constitute the exogenous governance structures of social innovators with the purpose of leveraging governmental, policy and financial support (policy changes, public subsidies, financial incentives, program experimentation) [11,21].
Both endogenous and exogenous institutional capital share three key components: shared knowledge resources, relational resources and mobilization capacity [23,25]. New forms of institutional capital are built up through exchanges of different forms of local knowledge and of analyses of socio-spatial phenomena, the formation of new and extended webs of relations between and across socio-political actors in territories, as well as the development and dissemination of new discourses leading the design and implementation of actions. Such fermentation of territorial institutional capacity generates public policies and funding distribution for territorial social sustainability, and also nurtures an improved quality of governance cultures and ways of 'relating' and collaborating (i.e., inclusive, diffused, well-informed and open-minded) and acting (rapid and legitimate) [23].
Social innovators in housing systems (e.g., collaborative housing initiatives or homelessness NGOs)-individually and through their networks-build up institutional capital to promote their interests in housing governance and policy arenas. Through novel multi-level interactions, their political objectives are to become more influential in advancing the housing and social conditions of people who are excluded from the housing market, to gain better access to deeper financial subsidies for affordable housing provision as prominent and appreciable territorial shapers, as well as to set in motion open, transparent and respectful housing arenas co-led by pro-poor/anti-speculation institutional actors [12]. As stated by Paidakaki [21] (p. 18), "to accomplish these objectives, housing social innovators act in different ways in terms of what and how to demand and whom to target. Some fight against displacement, gentrification and exclusion while others fight for housing and tenants' rights, fair rent, rent regulation, housing accessibility/affordability, new public housing construction and deeper public subsidies for social housing. Their tactics and strategies cover a wide range of actions, from eviction blocking, street demonstrations, political mobilization and electoral participation, to legislative/programming/policy lobbying, campaigns and urban plan proposals targeting powerful groups/opponents (e.g., pro-growth housing developers), public authorities and elected officials". Institutional capital thus shifts the focus of urban planning from constructing the built environment to fostering the institutional capacity in territorial political communities to co-shape sustainable communities.
According to Healey [24], citing Amin and Thrift [33], an innovative territory is characterized by abundant civic actors, a high level of social interactions between and across social groups, coalitions crossing individual interests of organizations and a strong sense of common purpose promoting innovation, economic growth and social cohesion. A territory with a high level of institutional capacity is a social and physical space that is continually emergent and changing in relation to framing and acting, and is informed by the three main features of institutional capital [23].
Against this backdrop, the conceptual framework for our empirical study focuses on the governance pillar of social sustainability in urban housing by incorporating insights from bottom-linked and institutional capital theories (see Figure 1). More precisely, we conceptualize the governance of social sustainability in urban housing as the interplay of interactions between the level of bottom-up social innovators (Level 1) and the level of top-down receptive institutional actors (Level 3), which results in a third, intermediate level of bottom-linked governance processes (Level 2).
Moreover, this governance pillar interacts with two important dimensions of social sustainability in housing, which we consider in our study [2,4,34]. The first dimension is social equity, which has its foundations on the concept of social justice and fairness in distribution of urban resources. The second dimension is the sustainability of community or the functioning of a community as a collective. It can be broken down into the dimensions of social interaction, participation, sense of place, residential stability and security. In our study, we will not consider these dimensions separately but consider community cohesion as an aggregate theme. We also bear in mind the contradictory relationship between the two dimensions of social equity and community cohesion and that governmental, business and civil society actors often have different aspirations and interests regarding transitions to social sustainability in housing and cities more generally. Thus, while the civil society housing alliances examined in our paper address both conflicting social sustainability dimensions to varying degrees, it is only through multi-level and bottomlinked governance that some compromise and balance between different goals related to social sustainability in housing can be found [35].
Thus, we understand social sustainability in urban housing as a profoundly multigoverned, inclusive and democratic transformative process led by rich institutional capital and new governance cultures for the production of housing programs and projects for all (e.g., market-rate, medium/low/no-income populations, ethnic communities) and by all (e.g., for-profit and non-profit housing developers, collaborative housing initiatives, homelessness NGOs).
Nevertheless, social sustainability remains a fundamentally place-specific concept. Therefore, it needs to be carefully considered for every city and even neighborhood. This contextual character of sustainability is of high importance for policymakers when they look at best practices for transfer to other contexts and cities.
To understand and dig into the transformative potential of alliances of bottom-up social innovators in realizing social sustainability in urban housing, the next two sections empirically investigate the unique histories and politico-institutional features of two civil society housing alliances, 'BAWO-Bundesarbeitsgemeinschaft Wohnungslosenhilfe' (in short: BAWO) and the 'Initiative Collaborative Building & Living' ('Initiative Gemeinsam Bauen & Wohnen', in short: IGBW), both based in the city of Vienna in Austria. This investigation focuses on the housing market dynamics-and the political climate therein-as it unfolded between 2014 and 2020. A brief look at these two examples of housing alliances in the context of Austria can help us gain an empirical understanding of social sustainability in housing from an institutional capital perspective and evaluate how, individually and interactively, these housing alliances attempt to realize social sustainability through the promotion of new housing policy and governance cultures in the country. In the following sections, we examine each case in relation to their unique histories, endogenous and exogenous institutional capital, claims and advocacy strategies, including how they sow the seeds of bottom-linked governance that would lead to housing for all. This examination is embedded in Vienna's housing market policy and context presented here below.

Examining Civil Society Housing Alliances in Vienna, Austria
As compared to other EU countries, the Austrian housing system has provided relatively stable housing conditions, even in the aftermath of the Global Financial crisis of 2008. This might also be due to its tradition of state intervention in housing based on a long-term party-political consensus. Yet, regulatory competencies are strongly split between the different state levels with limited responsibilities of the central state government. Relevant national regulation refers to the 'Tenancy law' for private rental housing and the 'Non-Profit Housing Act' that outlines important governance principles for non-profit housing providers across Austria, such as cost-covering rents, the requirement of reinvesting profits into their own construction business and compulsory state and sector internal supervision [36]. Non-profit and municipal housing play a comparatively important role in Austria, accounting for 20% of the total housing stock and 51% of the total rental stock.
However, it is particularly the regional or provincial state level that plays an important role in the multi-level governance of Austrian housing. Since the reforms in the late 1980s, regional provinces have been able to design their own housing subsidy schemes with co-financing coming from the national state budget. The focus is on supply-side subsidies for affordable housing provision by non-profit housing associations that apply for specific housing projects. The subsidies are subject to the fulfillment of certain conditions such as quality standards, maximum rent levels and the offer of a tenure mix. However, these conditions vary among the provinces and, for instance, do not explicitly consider the specific requirements of the emerging collaborative housing sector. Vienna has become a notable exception; the capital city, which is a regional province at the same time, explicitly introduced a set of criteria related to social sustainability in their housing developer competitions for public funding, which are always linked to specific plots in the city [37]. While in other Austrian provinces, the supply of inexpensive land is increasingly constrained by a lack of political will, Vienna continuously makes inexpensive building sites available to non-profit housing developers.
Vienna's reputable social housing system has its roots in the development of a successful top-down model of the Social Democratic welfare state of the inter-war period of the 20th century. Vienna is a city where 77% of all flats are rentals and with an extraordinarily large share of social rental housing (44%) as compared to other cities on an international level. These social rental apartments are either owned and administered by the City of Vienna (municipal rental flats), which mainly targets the lower-middle classes, or managed by housing associations (non-profit rental flats), which mostly cater to the middle classes. Since the 1990s, non-profit housing associations have become the main providers of new affordable housing in Vienna, steered by the city administration and its social housing policy [38][39][40].
However, among the 33% of the Viennese population that reside in free market housing, there is a private rental segment with a high concentration of migrants living in substandard housing conditions [21,40]. Access to non-profit and municipal housing in Vienna is extremely difficult, especially for recognized asylum seekers, due to preferential allocation rules that favor long-term residents and the middle-class and due to a general increase in housing demand [41]. Housing associations only occasionally offer flats to very vulnerable people in cooperation with homelessness NGOs. Table A2 in Appendix A provides an overview on the size and share of housing sectors and tenure types in Vienna.
Over the last decade, affordable housing in Vienna has come under pressure due to high population growth and slow provision of new subsidized housing that cannot keep up with the demand. In fact, public expenditure for housing decreased by 33% between 2007 and 2017 [42], which is also related to the need to comply with the 'Stability and Growth Pact' of the European Monetary Union. The EU's fiscal policy regime has clearly constrained room to maneuver for supply-side subsidies. In contrast, new construction activity has been led by private developers with a substantial amount of production of high-end apartment complexes targeting wealthy foreigners and investment funds [43]. As a consequence, market rents sharply increased by 28% in the private sector between 2008 and 2014. This has especially negatively affected the low-income segment in the private rental market; furthermore, homelessness increased by 32% between 2008 and 2016 [44,45].
These developments have made it difficult for proponents of an emerging collaborative housing sector (gemeinschaftliches Bauen und Wohnen) to establish their projects on the private market in Vienna. Nevertheless, the introduction of 'social sustainability' in the specifications for developer competitions was an important milestone in 2009. Although concepts of economic and ecological sustainability were already introduced in 1995, adding this 'social pillar' of sustainability provided much more legitimacy to resident participation and community building in mainstream social and non-profit housing in the city [37]. Since then, housing subsidies have been provided for architectural innovations for communal facilities and also professional consulting for community building among residents. In contrast, pioneer collaborative housing projects in Vienna, such as the 'Sargfabrik' in Vienna's 14th district (finalized in 1996) were substantially bottom-up self-help projects and its founders had to be extremely creative to access at least some kind of subsidies by framing the housing scheme as a 'dormitory' [46]. This situation changed dramatically when a Social Democrat-Green Coalition government came to power in Vienna in late 2010 and subsequently facilitated direct access for 'Baugruppen'-a nowadays commonly used label for collaborative housing-to land and public funding. The incoming government enabled specific developer competitions for Baugruppen projects as part of new housing and neighborhood development areas in different parts of the city [36]. Competitions usually focus on larger construction sites that clearly favor professional non-profit housing developers with a proven development track record. This is one of the reasons why partnerships between resident associations and a non-profit housing association have recently become a preferred approach to professionalize the process and facilitate access to subsidies for Baugruppen in Vienna [46]. Some projects highlight inclusiveness by providing flats to vulnerable groups on the housing market, such as recognized refugees. In those cases, social care providers (such as Caritas and Diakonie) as well as social/homelessness NGOs (such as neunerhaus) provide external expertise to project development and management, such as the project 'Oase.inklusiv'. One potential conflict that can arise from 'Baugruppen in partnerships' within the framework of subsidized housing is that both the municipality and a non-profit housing provider allocate flats in Baugruppen projects to residents from their own waiting lists. On the one hand, this might pose a challenge to the community building process, but on the other hand, it leads to more social inclusiveness in collaborative housing models [5]. Finally, the promotion of social sustainability in Vienna's housing policy approach has also led to the emergence of larger (about 100 units), more top-down collaborative housing models (such as the project 'So.vie.so') initiated by housing associations where tenants participate in a predesigned structure offered by external consultants [46].

BAWO: An Alliance of Homelessness Service Providers
BAWO is the Austrian national platform of social non-governmental organizations (NGOs) providing assistance to the homeless. Founded in 1991, BAWO aims to co-ordinate supra-regional tasks and to provide targeted public relations work to combat and eliminate the housing shortage and homelessness in Austria [47]. Since 2017, BAWO has emerged as a homelessness and affordable housing actor (Interview, 29 May 2018). The new goal of the umbrella organization has been to promote access to affordable housing in the private sector for poor/low-income and homeless people. In light of this new focus, in 2019, the umbrella organization was rebranded to 'BAWO-Housing for All' (Interview, 11 March 2020).
BAWO has remained a small organization. In 2020, BAWO's members amounted to 56 NGOs and 89 individuals. Most members of BAWO are practitioners coming from the base/grassroots. As they do not hold managerial positions, they do not find themselves competing with each other for funding. This allows them to work collectively in their effort to trigger changes for the benefit of their target clients. The board of BAWO has 18 members representing all Austrian provinces. Since 2019, the Secretariat of BAWO consists of two staff members, an administrative staff and a managing director dealing with policy issues and writing policy papers. The organization is financially supported by funds raised in their yearly three-day symposium (around 250 participants) and various of their projects have been supported by different organizations such as the Ministry for Social Affairs, 'FSW' (Fonds Soziales Wiem) and 'IBA' (the International Building Exhibition) (Interview, 11 March 2020).

BAWO's Endogenous Institutional Capital
BAWO is organized around province-based working groups. Advocacy work is conducted by provincial level board members and BAWO's chairperson at the federal/national level. These multi-spatial advocacy actions are the result of a decentralization of responsibilities regarding social and housing matters from the federal government to provincial governments. The national government has no competency to put direct pressure on the provinces on social and housing affairs; nevertheless, different national public authorities can build up pressure and persuade regional governments on certain issues. For example, in 2019 the Austrian Ministry of Social Affairs became interested in promoting the 'Housing First' model to tackle homelessness across Austria. For this purpose, it commissioned BAWO to conduct a study on the effectiveness of the model and in turn, used the study's results to influence regional governments to consider the model in their social and housing strategies. The Western provinces, governed by the Popular party as well as Vienna governed by the Social Democrats and the Greens, have been those ultimately promoting the model and being largely open to social affairs and affordable housing. BAWO's most advocacy priorities have traditionally focused on the allocation of state funds for the homeless, housing speculation and awareness raising through homelessness statistics (Interview, 11 March 2020). Especially housing speculation and rising prices on the housing sector have emerged as a major problem for homeless people looking for affordable apartments in every Austrian province [44].
At the national level, BAWO's members learn from each other, mainly during workshops organized during its yearly symposium for knowledge exchange. At the provincial level, the managing director visits the regions and participates in gatherings of people working on homelessness in each province to discuss practical problems confronted on the field. Following these gatherings, the BAWO secretariat provides an overview of the most prominent problems and strategizes around solving them at the national level (Interview, 11 March 2020). BAWO also writes policy papers with commonly agreed minimum standards used by their members to promote changes in their provinces and to apply for projects [44].
BAWO's policy papers also play the role of raising awareness within BAWO and the homelessness sector at large, explaining in detail the importance of housing and its use as an instrument to solve homelessness. This awareness raising is important in a sector where practitioners have focused more on alcohol and drug use, etc., and have paid less attention to structural issues such as housing markets and tenancy law (Interviews, 23 May 2018 and 11 March 2020). Members of BAWO also benefit from promotional activities led by the Secretariat, who attend homelessness-related events across the country and discuss homelessness and affordable housing issues with politicians. They also use 'FEANTSA' (the European Federation of National Organizations Working with the Homeless), of which BAWO is a member, to bring important issues to the fore at the European level and to learn about best practices in other EU countries in order to lobby for these at the national level (Interview, 11 March 2020).

BAWO's Exogenous Institutional Capital: Genesis and Further Development
In 2015, BAWO began focusing on housing and the novel connection between housing and homelessness, having a clear initiative for dealing with housing policy from the perspective of homelessness. For this purpose, BAWO received funding from the Ministry of Social Affairs to organize three expert workshops in which a large pool of more than 45 participant experts in the fields of housing development (including private real estate sector and limited-profit housing sector, e.g., GBV, CEOs of housing associations), housing and tenancy rights, housing politics and homelessness services participated and interacted with each other (Interview, 29 May 2018). The goal and expected outcome of these workshops was to build, reinforce and intensify the connections between the social sector and housing sector and promote BAWO as an expert in housing policy [21]. The strategy of BAWO was to convince housing actors (city, non-profit sector) that there is a need to connect the housing allocation system (one-third of the flats) with the homelessness sector, since access to social and especially council housing had become stricter [21]. In 2017, BAWO considered that it was the right time to lobby for 'housing for all', as all the more people became homeless or were trapped in the homelessness sector, no options existed for the homeless people to exit the system and no cooperation was in place between homelessness organizations and social housing associations. During the three expert workshops, the discussion mainly focused on strategies and solutions to guarantee decent housing for homeless people (not only rough-sleepers but rather a broad target group, including low-income people) (Interview, 23 May 2018).
The workshop series was translated into a policy/position paper on affordable housing based on inputs and expert knowledge from the large pool of workshop participants. The policy paper titled in English 'HOUSING FOR ALL. affordable. permanent. inclusive' (in brief: Housing for All 1.0) was published in 2017 with funding from the Department of Social Affairs and organizational support and expert knowledge from the Austrian National Bank. It pointed out that services for the homeless people and other vulnerable groups, though having an important supportive role, cannot be considered a structural or sustainable solution to the housing crisis [44]. Housing for All 1.0 elucidated the critical housing shortage situation for households on lower income and presented eleven policy actions that can address the lack of adequate housing in Austria [48] (see more in Table A3 in Appendix A). With its focus on affordable housing for low-income people, BAWO's policy paper aimed at promoting the societal goal of providing 'housing for all'.
The end of this first phase of inter-institutional interactions laid stepping stones for novel exogenous institutional capital marked by an understanding that BAWO is part of a broader inter-institutional housing coalition that fosters a 'housing for all' policy centered on the needs of low-income groups. One way of promoting such a policy, seen by BAWO as "a crucial social challenge for the future", has been the successful bridging between key actors in housing and social politics [44] (p.3). As a result of such interactions, the policy paper also become a collective lobbying instrument of BAWO to demand more and better affordable housing (both from the income and cost perspective) for housing for low-income groups (Austrian homeless, refugees) for homelessness prevention (Interviews, 23 May 2018 and 11 March 2020). The paper was presented at BAWO's annual conference, where deliberations took place on how BAWO could work further with it; it was presented to public authorities (city of Vienna, Ministry of Social Affairs) and elected officials (Social Democrats, Popular Party) to put affordable housing (higher) on their policy agendas. Members of BAWO used the paper to lobby for housing for all on the provincial level, while BAWO members from Vorarlberg and Upper Austria made their own policy papers that were tailored to the conditions in their provinces (Interview 11 March 2020).
As a consequence of the participation of limited-profit housing associations in the process (workshop and paper drafting), GBV did a survey of the social projects and initiatives in the housing stock of their members. This also triggered discussion around issues (eviction prevention, access to the housing market by homeless), ventilated good practice across GBV members and intensified cooperation between GBV and BAWO at the local level of their member organizations (Interviews, 29 May 2018 and 20 February 2020).
Following the workshops and the policy paper, BAWO deliberated on organizing a new round of expert workshops inviting housing professionals to discuss the issue of access to social housing-a topic that has been controversial in the last decades in Austria-and seek answers to questions such as: Is social housing (in Austria) for the people that need it the most? Is it a goal? Is social housing providing housing also for higher income groups? Does Vienna have a too big a proportion of social housing? These questions cast light on the need for access to social housing for low-income people while claiming that social housing is for everybody (Interview, 29 May 2018).
Connecting the social sector with the housing sector remained a major concern for BAWO in the years following the first phase of interaction between the homelessness and housing sectors. Rebranded as 'BAWO-Housing for All' (in brief: BAWO), they continued leading the expansion and solidification of the 'Housing for All' informal alliance with experts working in the fields of housing construction, housing law, housing industry, social affairs, homeless assistance and science aiming to improve housing provision in Austria. Through a new series of workshops and the preparation of a policy paper sequel, BAWO has offered a solid platform for participants to develop a common language, a common awareness of problems and jointly support suggestions for improvement [49]. It has continued increasing awareness on the special needs of homeless people to representatives of the housing sector and reinforced connections and partnerships between social organizations and housing developers (especially limited-profit housing associations, which are the main affordable housing providers in Austria).
BAWO has maintained good relations with Ministry of Social Affairs and GBV, both of which support their work and participate in their workshops and its yearly symposium. BAWO benefits from interaction with GBV in terms of knowledge, door opening (workshops become more popular with GBV's presence), dissemination of BAWO's policy papers and awareness raising across GBV members (through their newsletter and invitations to participate at BAWO's annual conference) (Interviews, 20 February and 11 March 2020). At the same time, BAWO has continued its efforts to reach out to individual housing associations and its members collaborate in parallel with individual associations at the organizational level. An expansion of such collaborations, especially for Housing First projects, have remained vital for BAWO and their clients in times when new housing construction by limited-profit associations is unaffordable and waiting lists are long making it hard for homeless people to get into the non-profit housing stock in a more efficient way, especially as housing dedicated to very vulnerable and low-income target groups is not GBV's main field activity. In its effort to get housing builders to understand that they can benefit from building the right houses/flats for people who are not very rich and dedicate 25% of the flats for BAWO's clients (homeless, the most vulnerable), BAWO expanded their network of partnerships by establishing a new cooperation with IBA (Interview, 11 March 2020). The previous phase of inter-institutional interactions led to the importance of more knowledge on and recording of homelessness that led to a fruitful cooperation with Statistics Austria (BAWO conducted two projects with them to enhance research strategies for obtaining statistics on homelessness) [49]. At the level of member-organizations, some BAWO members are also well connected to banks (e.g., neunerhaus collaboration with Westernbank) (Interview, 11 March 2020).
Despite the network of already established partnerships, BAWO lacks connections with commercial developers that are considered hard to reach and that are not interested in such partnerships when the market favors skyrocketing rents. BAWO's strategy to ensure the private market dedicates a percentage of their flats on discount to low-income people is only through advocacy at a political level, reminding the state of their obligation to deliver 'housing as a social right' and put housing over personal profits. Another housing actor group with which BAWO does not ally are the collaborative housing initiatives, which are considered to be targeting mainly the middle class and people with similar mindsets (living collectively)-a relatively expensive housing solution that is seldom compatible with homeless people who also need a fine balance between inclusiveness and anonymity. BAWO does not see collaborative housing as an effective solution to tackling homelessness (Interview, 11 March 2020).
BAWO made a sequel policy paper ('BAWO Housing for All affordable permanent inclusive', in brief: Housing for All 2.0), published in 2019 (see more in Table A4 in Appendix A) with project funding from the Ministry of Social Affairs and the support of Vienna Chamber of Labor. Housing for All 2.0 maintained more or less the same content as the previous paper but added voices of BAWO's wider network-including the former UN rapporteur on the right to adequate housing, the national bank, FEANTSA and the anti-poverty network, all of which aimed at promoting both the paper and BAWO's work in general. Housing for All 2.0 was drafted by BAWO following the views exchanged by experts and their input when participating in the workshops designed to develop the content of this policy paper/building on the wide-ranging expertise from people from different fields all concerned for housing for all [49]. The paper also celebrated the positive and powerful effect of promoting housing for all collectively ("Together we can do more. Positively promoting housing for all" in p. 24) and the consolidation of a new BAWOled loose alliance. The paper makes concrete demands relating to housing, income and social participation with the aim of changing basic housing and socio-political conditions in such a way that fewer people are affected by homelessness and develop sustainable solution strategies.
BAWO's aim with this paper sequel was the introduction of their overarching strategy and specific measures relating to social and housing policy for affordable, permanent and inclusive housing in discussions with decision makers and in order to promote the strategy's implementation. For each of the demands, the target public authority/politician for lobbying was different. Using material from the paper, BAWO's managing director wrote an article on housing and the right to housing in the Constitution for the report of the human rights league of Austria targeting the United Nations. The new policy paper was disseminated across the provinces for their members to offer copies with their local politicians during advocacy meetings and was shared in press conferences on affordable housing to journalists for awareness raising. On a different scale, BAWO used the paper to interact with FSW on issues regarding rents and tenancy laws and find ways to collaborate together for change making. However, for BAWO to make significant changes on the tenancy law, the Ministry for Economic Affairs remained yet to be reached out to, a task that became one of their goals for 2020 and 2021. For other issues (e.g., allocation premium, the right to housing in the Constitutions, the rectification of Articles 30 and 31 of the European charter), as of 2020, BAWO still needed to find access to and fix appointments with the then new national administration whose cabinets were not yet fully developed and in full swing, making lobbying activities challenging in the first period after elections.
On a practical scale, BAWO has aimed to promote inclusive and affordable permanent housing with IBA focusing on practical issues such as number of rooms, square meters and people's needs. BAWO has also recognized the limited influential power of position papers and the limited action-making capacity of a part-time Secretariat (Interview, 11 March 2020)

IGBW: An Alliance of Collaborative Housing Initiatives
In 2009, IGBW was founded as a representative body and umbrella association for collaborative housing initiatives in Austria. The key goal of IGBW is to foster "( . . . ) the establishment of legal, organizational and economic conditions which allow people to initiate and realize self-controlled and collaborative housing projects" [50]. In contrast to the established non-profit housing umbrella body GBV, it is a rather small and loose organization that promotes collaborative building activity among different stakeholders (e.g., architects, developers, politicians) and serves as a platform for networking, knowledge exchange and support for people interested in the concept of collaborative housing (Interviews, 1 December 2014 and 10 April 2015).
IGBW currently has 80 active members, most of which are individuals, with a handful of organizations. Individual members are (potential) residents of collaborative housing projects as well as architects, sociologists and urban planners who promote this housing concept (Interviews, 1 December 2014 and 9 March 2020). IGBW's board consists of seven members that meet once a month; the general assembly is attended by all members and meets annually. IGBW's basic statute mainly focuses on elements such as entry or exit [49]. Financing primarily comes from the yearly membership fees that help organize workshops and events (Interview, 9 March 2020).

IGBW's Endogenous Institutional Capital
Similar to other European countries, the collaborative housing sector in Austria cannot be reduced to a single development model or to specific locations [46]. Collaborative housing forms vary in terms of, for instance, tenure, legal and organizational characteristics. Projects in Austria are in line with the general definition of collaborative housing, referring to a substantial degree of collaboration and social interaction among residents who share a set of core goals and motives in relation to communal living and societal development such as fostering ecological sustainability and social inclusion [51].
IGBW focuses on promoting the general concept of collaborative housing and thus, in principle, represents diverse models, including the urban Baugruppen, but also more rurally based CoHousing projects. However, IGBW's activities are in fact focused on Vienna, which has seen considerable Baugruppen activity linked to political interest and some state promotion over the recent decade (Interviews, 1 December 2014 and 29 October 2015).
IGBW's advocacy work focuses on the limited responsiveness of the Austrian regulatory framework to the needs of various collaborative housing projects, in terms of issues such as suitable legal forms, funding programs and access to land. IGBW proposes pragmatic solutions to these issues or minor regulatory adaptions that address their members' needs, but are still acceptable to policymakers and local authority officials (Interviews, 10 April 2015 and 9 March 2020). The concept of collaborative housing is not well known nor easily understood in Austria. As such, another important part of IGBW's activities concerns awareness raising among the general public and policymakers regarding benefits and pitfalls of developing collaborative housing, as the following quote highlights: "You have to be able to understand the benefits of such a model before you can promote it [ . . . ] if you want politicians to support something, you have to give them arguments that they can use" (Interview with former head of IGBW, 9 March 2020).
Such arguments can refer to benefits for residents, the wider neighborhood or urban development. In that sense, IGBW, for instance, addresses municipalities' common concern that their provision of funding and land could ultimately benefit only a very small group of residents in urban areas (Interview, 1 December 2014). It is important for IGBW to have direct personal contact with politicians and also to reach out to various stakeholders in urban development and the wider public through events, talks and discussions. During these outreach activities, topics are addressed such as the specific requirements of community groups in developer competitions or the adequate urban development areas for project implementation (Interview, 9 March 2020).
Commissioned research has become another means to raise awareness on collaborative housing. An example is a research project that was carried out in 2015 and resulted in a series of papers on the quantitative demand for collaborative housing in Austria and specifically in Vienna. The papers provided a platform for a debate between IGBW representatives and the city administration on contested issues, such as the allocation of flats in collaborative housing schemes built with subsidies by the local authority (Interviews, 10 April 2015 and 9 March 2020).
However, IGBW's awareness raising and knowledge exchange also targets its membership and wider supporter base. Regular communication is done via a monthly newsletter, social media platforms and the webpage. There is regular interaction between 20 to 35 community groups, not only from Vienna, but also from other parts of Austria, that are in different stages of developing projects and seeking additional members. In response, IGBW recently organized a series of workshops to address issues in developing collaborative housing, such as financing, mobility or group building (Interview, 9 March 2020).
IGBW does not have established partnerships with institutional actors from other housing sectors, such as GBV, nor with NGOs (e.g., BAWO, neunerhaus) and social welfare organizations (Caritas and Diakonie) that advocate 'housing for all' (Interviews, 17 December 2014 and 11 March 2020). However, such partnerships have recently emerged on the level of individual Baugruppen projects in Vienna.
In parallel to the development of IGBW, support and facilitation structures for specific forms of collaborative housing in Austria have emerged. One example is 'Die WoGen', a developer for new collaborative housing projects (in the legal form of small cooperatives). It was founded in 2015 and acts similarly to what is internationally known as a 'secondary housing cooperative'. Another example of a recently founded secondary service provider in Austrian collaborative housing is the 'Dachverband habiTAT', which has supported the development of a few bottom-up housing projects in major Austrian cities (Focus Group, 29 October 2015).
The emergence of different umbrella bodies, such as Die WoGen and Dachverband habiTAT, highlights a certain degree of fragmentation in the collaborative housing field in Austria, also in terms of advocacy work and member representation. This might also explain the rather loose character of IGBW as a national advocacy body for collaborative housing that does not promote a specific model of development. Nevertheless, the different umbrella organizations do not compete but see themselves as fulfilling different but complementary goals in the sector (Focus Group, 13 June 2018).

IGBW's Exogenous Institutional Capital: Genesis and Further Development
Austria has a rather long history of collaborative housing activity that goes back to the cooperative settlers' movement of the 1920s; this movement represented a contrasting model to the top-down and large-scale social housing development promoted by the municipality in the interwar-period. The 1970s and 1980s saw another wave of self-organized housing projects which was partly linked to an ambitious research and evaluation scheme funded by national government (Interview, 1 December 2014). However, as a movement, collaborative housing never reached a substantial level of institutionalization going beyond single showcase projects. The limited growth of the sector is potentially linked to the generous Austrian welfare system, which has always offered good quality and affordable housing to a large part of the population. There are also cultural obstacles to collaborative housing in Austria, as norms of cooperation and self-initiative in housing contrast to traditions of paternalism (Interview, 10 April 2015 and Focus Group, 29 October 2015).
In the first decade of this century, several housing theorists, architects and some resident groups engaged in campaign and lobbying activities towards mainstream collabo-rative housing ideas in Vienna, clearly influenced by the growing Baugruppen movement in Germany (Interview, 1 December 2014). The foundation of IGBW in 2009 is linked to a changing policy environment for housing in Vienna, which started to become more receptive to the concept of 'social sustainability', as well as ideas of resident participation and community building within the framework of subsidized urban housing (Interview, 29 October 2015). Already in 2009, one of the IGBW founders was involved in a major research project to explore the conditions for implementing the Baugruppen model in the Viennese context [52]. The study received funding by the municipal housing research department. Drawing on the expertise of a reputable Austrian social research institute, the study provided initial evidence on the demand for collaborative housing in Vienna and directly addressed the municipality with a set of recommended measures to support Baugruppen projects.
Building on this scientific evidence base, the Green party positioned itself as an advocate for collaborative housing ideas in the run-up to the 2010 local elections in Vienna. There was one especially influential Green Party politician with whom the founding group of IGBW eventually established good relations (Focus Group, 13 June 2018). The elections resulted in the formation of the first ever coalition government between the Social Democrats and the Greens, in charge of the urban development agenda while housing policy was still controlled by a Social Democratic minister.
IGBW's lobbying and advocacy activities resonated with Vienna's new housing policy lead theme, 'social sustainability'. The incoming Social Democrat-Green Coalition started to engage in a more direct promotion of collaborative housing projects through facilitating access to land and public funding for Baugruppen projects. This new policy approach materialized in the launch of the first ever developer competitions for Baugruppen (Interview, 29 October 2015). In the Viennese neighborhood Seestadt Aspern-one of the largest urban development areas in Europe in recent years-for the first time, the city administration made building plots available directly to five collaborative housing projects in 2012, which were finalized in 2015.
The former head of IGBW recalls how Baugruppen projects in Aspern came into existence: "Between the center and the outskirts there has been an urban development area which was quite disconnected from any other infrastructure. And they (the municipality) started to develop it and thought we needed to bring people there in the first place, so like pioneers, who would have some kind of interest to identify themselves with that new area. They thought that collaborative housing could be a good vehicle to not only bring active people there but to also promote this kind of alternative development approach" (Interview with former head of IGBW, 9 March 2020). For IGBW, the success with Baugruppen in the Aspern urban development area represented a unique opportunity to raise even more public awareness for their concerns and to link these to additional research commissioned by the municipality. The realization of Baugruppen projects in the Aspern neighborhood in Vienna between 2011 and 2015 helped IGBW in their strategic positioning activities within the wider institutional environment of housing and urban development. Building on the activities in Aspern, IGBW promoted the inclusion of Baugruppen in every new urban development area with a certain amount of fixed plots. In their external promotion and advocacy efforts, IGBW could now point to actual housing experience on the ground and successful showcase projects that also represented different legal and organizational approaches of collaborative housing (Focus Group, 29 October 2015).
Indeed, new opportunities emerged with developer competitions for Baugruppen in other urban development areas, such as in the Sonnwendviertel at the new central train station, or in Neu-Leopoldau. IGBW considers this a major success of their activities. Since 2015, Baugruppen-as one specific model of collaborative housing-has become an established tool of housing and neighborhood development in the city. IGBW gained legitimacy as a representative of Baugruppen projects and the topic of collaborative housing in general. At the same time, it recorded a membership growth from 50 to 80 (Interviews, 1 December 2014 and 9 March 2020).
Having had the experience of developing Baugruppen in Aspern, IGBW realizes that under the current institutional conditions of social housing, it is beneficial for collaborative initiatives such as this one to form partnerships with larger non-profit and cooperative providers. These developers are in a better position to access funding and also secure sites in developer competitions due to their reputation, professional expertise and financial strength, all of which helps to prefinance projects. Thus, IGBW has begun to promote this partnership model, among different options, while at the same time stressing its potential pitfalls, such as limiting the self-organization of residents (Interview, 10 April 2015 and Focus Group, 13 June 2018).
More generally, IGBW started addressing fields of tension that emerge when building collaborative housing within the framework of subsidized housing in Vienna. It also challenged the municipality (and especially the Social Democrat-led housing department) on its position towards these issues. One main point of conflict centered on the issue of accessibility and external allocation to Baugruppen projects. The Social Democrat's position-though not always clearly articulated-is that the provision of public subsidies requires Baugruppen to accept that a third of all flats should be allocated directly through municipal housing services. However, the practice of dividing flat allocation between the core resident group (e.g., a tenant association), the municipality and possibly also a nonprofit housing provider, is problematic for community building, as tenants have diverging interests, expectations, motivations and pre-existing knowledge about collaborative forms of living (Interviews, 10 April 2015 and 9 March 2020).
As a consequence, it needs even more facilitation and moderation inputs by intermediary organizations. Against this backdrop, a handful of specialized architectural, planning and consulting offices in Vienna have come to play a crucial role in developing collaborative housing in Vienna and to a limited extent in other parts of Austria (Interviews, 17 December 2014 and 10 April 2015). There are overlaps between these intermediaries and IGBW, as the founders and key actors of organizations such as 'wohnbund:consult', 'raum & kommunikation' or 'einszueins Architektur' have also been actively engaged in IGBW. On the level of individual projects, these intermediary organizations facilitate community building and connect the needs of resident groups with the requirements of institutional structures, such as the relevant departments of the city administration and larger housing associations. Their role as intermediaries and project facilitators is pivotal because of their strong roots not only within the collaborative housing movement, but also their experience working for institutional and private actors in Vienna and beyond (Focus Group, 13 June 2018).
An important point of influence and lobbying for IGBW members became the stage of master-planning of urban development areas. In recent years, collaborative planning approaches have been institutionalized in Vienna, closely connecting area-based planners with developers, landowners and community work. Some consultancies work at this level, as do architects, to influence the design to lobby for collaborative housing access to land. Some influential academics also engage at this stage and promote ideas of collaborative housing within broader planning concepts of organic cities and smart cities. An example is a Professor for Urban Planning at the Technical University in Vienna and owner of a spatial planning office. The resident groups only connect after the master-planning decisions are made (Focus Group, 13 June 2018).
Nevertheless, even the experienced intermediaries in the collaborative housing field find it difficult to deal with specific low-income and vulnerable target groups, such as those of municipal housing in Vienna. One solution that recently emerged is to bring in NGOs as partners who regularly deal with vulnerable target groups, such as neunerhaus in the above-mentioned project Oase.inklusiv. While these collaborations are focused on the level of individual housing projects, a partnership between IGBW and BAWO does not exist (Interviews, 9 and 11 March 2020).
IGBW has begun to accept that some aspects of the regulatory framework of housing in Vienna are just difficult to change in the short run. Even without desired changes, such as in allocation rules, Baugruppen projects have continued to get off the ground and have been approved by local governments. At this point, there is no reason to believe that the successful promotion of collaborative housing in Vienna will change, even though the Social Democrats and Greens coalition recently came to an end. In the meantime, IGBW has returned to more awareness raising on the housing topic in general and has also started to promote combining ecological and social sustainability in collaborative living and building practice. The new goal is to find ways to introduce new sustainability qualities without raising the construction costs within the framework of subsidized housing and thus keep collaborative housing affordable (Interview, 9 March 2020).

Discussion and Implications
Our paper has analyzed social sustainability in the context of urban housing through the lens of institutional capital. We studied two civil society housing alliances in Austria, BAWO and IGBW, which represent pragmatic and formalized approaches to civil society action in affordable and community-led housing [53]. In particular, we explored how these two civil society actors develop endogenous and exogenous institutional capital over time and advance bottom-linked governance configurations to foster a more socially sustainable housing system in Vienna. In doing so, our paper contributes to recent scientific debates lying at the intersection of social sustainability, urban development and housing [4,5]. It also adds to an emerging stream of literature that deals with the re-emergence of collaborative housing organizations in Europe that aim to advance the social sustainability agenda [51,54]. We specifically advance the discussion on the governance politico-institutional innovations of alliances and umbrella structures in the collaborative housing sectors [55] and their impact on sustainable urban development [56]. Our longitudinal study shows how, over time, civil society housing alliances (including alliances of collaborative and communityled schemes) can influence sustainable urban development policy by pursuing their own agenda of public promotion for their housing solutions across the city. The findings of this study, nevertheless, have to be seen in light of two methodological limitations that could be addressed in future research. First, the study focused on two housing alliances in one single country, Austria. To further develop the potential that housing alliances have in advancing social sustainability, a larger sample of housing alliances needs to be studied globally. Second, to gain a deeper understanding of the institutional impact of housing alliances in shaping cities for all, multi-month ethnographic studies of housing alliances shall be conducted for primary data collection.
By reflecting on the institutional and relational character of the two housing alliances and the novel governance formations they led in the Austrian, and specifically Viennese, housing system, we now briefly address the initial research questions: What are internal governance features that characterize civil society housing alliances? What are their strategies of interaction with institutional actors in order to promote social sustainability and thus counter exclusionary patterns in urban housing systems? We then draw some important lessons on the potential and limitations of housing alliances in forming bottom-linked governance and fostering social sustainability in housing systems.
While both of our case study housing alliances are rather small in terms of membership and financial resources, BAWO's internal governance structure is much more elaborate, a possible outcome of its longer-term presence in the Austrian housing institutional arena as compared to the newly established IGBW. BAWO's regionally based board structure matches more closely the governance system on housing and social policy in Austria, whereby the regional provinces have considerable decision-making power. Such a structure seems favorable to civil society housing alliances in other countries that operate in a pronounced multi-level policy environment characterized by devolution of power to regions and cities and a heterogeneous political landscape. In contrast, IBGW has primarily focused its activities on the regional housing context of Vienna (though it was originally set up as a national advocacy association), due to the capital city's socio-demographic dynamics favorable to collaborative housing initiatives, and due to the recent receptivity of the Viennese housing policy environment to ideas of collaborative housing as compared to all other Austrian provinces.
The two organizations under study activated their knowledge resources, contacts and mobilization capacity to advance the substantive and procedural aspects of social sustainability. They steered residential developments through targeted institutional support for novel governance configurations and a wider range of housing alternatives. Both umbrella organizations have applied similar mechanisms in raising awareness through workshops and commissioned studies by government departments, for example, to advance their advocacy priorities (i.e., housing for all through housing affordability, accessibility to land and community cohesion: all fundamental elements of the substantive aspect of social sustainability in housing systems). BAWO's focus has clearly become affordable housing, and through its members it represents the interests of vulnerable groups on the housing market. At first sight, IBGW seems to have a rather contrasting position, since collaborative housing is often only perceived as a middle-class housing model, reflecting a particular lifestyle, but not considered to be affordable in principle due to the additional requirements related, for instance, to community spaces. However, both housing alliances contribute to an agenda of 'housing for all' and advance social equity and democracy by advocating the inclusion of relevant topics and groups (e.g., homeless, community and neighborhood support, resident participation) into a subsidized housing framework, which even in Vienna often results in housing projects that foreground the interests of the middle-class and promote individualism.
Nevertheless, both alliances essentially represent the needs of individuals and social groups excluded by the housing market, i.e., homeless people and people interested in community living. Therefore, they find it difficult to attract significant and continuous institutional support for their agendas from the main governing parties. Nevertheless, the case of IGBW suggests that it is important to build informal alliances with individual policy makers who eventually help to shape the government's housing and urban development agenda in favor of balancing two central but conflicting social sustainability goals: sociospatial equity and community cohesion.
Both alliances have built up a growing exogenous institutional capital in their respective sectors (homelessness and collaborative housing) through the genesis of interinstitutional coalitions (see 'Housing for All') and an expansion and/or consolidation of partnerships with institutional actors, especially within the political world of Vienna, which has been more receptive to novel housing discourses and propositions (Housing First, Housing For All, collaborative housing) as compared to other Austrian provinces governed by the conservative party. This showcases a rich institutional capacity of housing alliances to relate to powerful decision and policy makers in order to build bridges between different 'policy worlds' (the social and the housing), steer new directions of territorial development through policy experimentations and victories (see Housing First study and the requirement of 'social sustainability' in development competitions) and form new governance cultures for the production of 'housing by all' (improving the procedural dimension of social sustainability in housing, at least in the regions with a favorable political and ideological landscape). Table A5 in Appendix A provides a summary of the key characteristics of the two case studies.
While our study reveals a multi-governed, dynamic and self-reflective (and often self-correcting) housing system in Austria, the novel institutional capital incubated by civil society housing alliances is rather fragmented. Our analysis shows that the policy instrument of social housing allocation becomes key to foster social inclusion in residential neighborhoods and has thus become a focus of lobbying activities by BAWO. At the same time, it provides risks for the interests of civil society housing alliances such as IGBW, which finds itself in a dilemma. On the one hand, it seeks to ensure affordability for collaborative housing schemes, while on the other hand, it lobbies for exceptions to resident allocations, such as by the municipality, to have as much independence and self-organization for intentional resident communities. This example encapsulates the complexity in the governance of urban social sustainability as a comprehensive and multidimensional concept which needs to find a balance between the two crucial elements, social equity and community cohesion as well as addressing specific and universal housing needs of residents (e.g., self-organization vs. affordability). It is these contradictions that seem to hinder the development of a richer, more inclusive institutional capital in the multi-level housing system of Austria. In our two case studies, for instance, we find that there is a lack of partnerships across civil society housing movements (between BAWO and IGBW) as well as between civil society and institutional actors in urban housing (e.g., between IGBW and the non-profit housing umbrella GBV).
To conclude, social sustainability in housing systems can be realized when it is set as a societal ambition sufficiently politicized by major parties involved in housing systems (housing alliances, governmental authorities of all ideological backgrounds, large nonprofit housing developers) that can collectively, and through thicker bottom-linked and co-linked governance arrangements, guarantee housing affordability and socio-spatial equity for all.
Author Contributions: Conceptualization, A.P. and R.L.; methodology, A.P. and R.L.; software, A.P. and R.L.; validation, A.P. and R.L.; formal analysis, A.P. and R.L.; investigation, A.P. and R.L.; resources, A.P. and R.L.; data curation, A.P. and R.L.; writing-original draft preparation, A.P. and R.L.; writing-review and editing, A.P. and R.L.; visualization, A.P. and R.L.; supervision, A.P. and R.L.; project administration, A.P. and R.L.; funding acquisition, A.P. and R.L. All authors have read and agreed to the published version of the manuscript. Acknowledgments: The authors are grateful to the anonymous referees for their valuable comments and suggestions on an earlier version of the manuscript, as well as to Liana Simmons for the high quality editorial work.

Conflicts of Interest:
The authors declare no conflict of interest. Table A1. Key empirical data sources (source: Authors).

Interviews
Type of Actor   Table A3. Key messages of the 2017 policy paper "HOUSING FOR ALL affordable. permanent. inclusive".

Key Messages Description
Problematizing the context While acknowledging Austrian's housing policy intention to serve a wide range of sections of the population and the existence of legal foundations that correspond to the government's objective to provide adequate housing for all (see the 'Tenancy Law' and the 'Limited-Profit Housing Act'), the paper problematizes the actual organization of the housing policy. The contrarieties in the systems lead to an insufficient supply of housing for low-income groups, as well as access barriers due to institutionalization dynamics and the exclusion of these groups in the allocation of subsidized apartments.
Housing for all: a way forward The paper calls for adjustments in existing housing policy (especially rental market policy considering all three market segments: municipal housing, limited-profit housing and the private rental market), a closer cooperation between the housing and social sectors and a scale-up of specific and focused interventions (such as specific allocation systems and special living situations) to ensure that low-income people are reached in a better way and housing policies are organized according to a real focus on 'Housing for all'.

Material and social criteria
Material criteria: Affordability; Housing Quality; Housing Stability; Location; Accessibility. Social criteria: Social inclusion; Professional Services; Prevention; Voluntariness and Accessibility; Discrimination and Stigmatization Avoidance. Table A4. Cont.

Key Messages Description
Problematization of the context The paper acknowledges the fact that the Austrian housing system has been cited as a best-practice example internationally and that housing quality has improved substantially over the years. However, the paper argues that indicators such as cost increases (particularly rising sharply over the past two decades), the lack of ratification of paragraphs 30 and 31 of the European Social Charter, which refer to poverty, social exclusion and housing, the lack of a permanent housing prospect bound by tenancy law and the availability and (over)use of homeless assistance services over time, show that housing in Austria has once again become a socio-political challenge and more efforts will be needed to secure an individually enforceable right to housing (BAWO Chair and UN Special Rapporteur on the Right to Adequate Housing).

Housing First promotion
Access to a permanent tenancy-also in expensive/gentrified areas-is a starting point for social participation and integration of homeless people in their local community. Housing also has a destigmatizing effect and promotes independent living.
Policies and Demands 1. Implement the human right to housing 2. Strengthen the rental sector 3. Lower housing costs and effectively limit profits earned through letting residential properties 4. Strengthen the legal framework for sustainable housing 5. Ensure non-discriminatory and inclusive access 6. Create more affordable, permanent and inclusive housing 7. Establish measures for a living wage 8. Strengthen the social security system through social security funds 9. Implement vital social assistance benefits at Federal and State level 10. Standardize and increase monetary benefits for housing 11. Improve stability and quality of life through a good home environment 12. Expand Housing First and other mobile support services