Cities are becoming the main model of human habitat, and it is urgent and important to study them, in order to face adequately the important future global challenges of sustainability and inclusivity. The contemporary city is subjected to processes of transformation that are generating within itself and at the borders new types of spaces. Among these spaces there are Terrain Vague, undeveloped spaces within urban areas, at different scales, where emptiness prevails over fullness and naturalness prevails over built, with unclear boundaries or thresholds. Emptiness can be thought as both negatively and positively, in fact, as referred by Solà Morales, the “emptiness, therefore, as an absence but also as a promise, as a contrast, as a place of possible and hopeful waiting”. These spaces can play an important role in promoting an inclusive, affordable, sustainable, resilient urban regeneration, by integrating the environmental approach, through the nature-based solutions, and the social approach, through the co-creation process. In fact, there is a correlation between green spaces accessibility and social equality. This paper presents a new approach to Terrain Vague spaces: no longer an approach based on land consumption, mono functionalism of spaces and zoning, but a more flexible, dynamic, and reversible approach based on human-centric design and identity embedded in situ. This new approach is based on time, system, participation, and diversity. In fact, Terrain Vague can be linked, creating a network of in-between spaces of transition, offering equal access to green spaces; they offer possibility of temporary alternative uses, engaging citizens and strengthen sense of community through bottom-up and co-creation process; they can generate the increase the economic value of neighborhood, stimulating urban regeneration. A new way of designing habitat based on diversity, which represents their greatest resource. Methodologically, the research follows a literature review comparison and shows an on-going mapping of Terrain Vague in the city of Lisbon as example. The preliminary results will discuss the potential of Terrain Vague related to habitat development, some holistic approaches involving different actors and how they strengthen communities including co-creation processes in sustainable habitat design.

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