What happens when one can not go out of the house or remain in it, when it is no longer possible to comply with spatial and time requirements of school or work? Then what does it mean “to "occupy" one’s days? What does it mean to live alongside teenagers or young adults, who withdrawn in their home, invade or disappear from common spaces? What does it take to adapt to their homelessness? How to make viable a disrupted daily life and how to deal with the hazards of family reproduction? The ethnographical investigation carried out in France between 2011 and 2014, among young people experiencing difficulties identified as associated with mental illness and their families, aims to answer these questions. From family monographs, supplemented with observations of medical interviews, home visits, various medical-social and health sessions, this investigation is devoted to the knowledge of their living conditions, in the context of family cohabitation. The omnipresence of withdrawal and homelessness practices, despite the diversity of individual situations, explains why they have become the object of this research. They are grasped as material daily experiences of time and space, socially situated. For many of these young people being excluded from the school system or labour market, homes are at the heart of their existences, concerns and arrangements. The symbolic breakdown that comes from discordances in their occupation of time and space and the destabilization of household economy explain their daily burden. The professionals who accompany the young people on a daily basis try to act on their schedules and their outings to set them in motion. This thesis deals with these young people and their family circle at a time of upheaval of their aspirations. Most of them are subjected to a worrying uncertainty, only some of them can think of access to schooling arrangements that safeguard a dreamful hope. The experiences and reactions of young people - withdrawal, anger, shame or homelessness - are shaped by the constraints (school, labour, family, institutions) that are exerted on them and by the injunctions to which they are subjected.