Governments in many developing countries still face the great challenge of responding to the increasing demand of low income populations for affordable housing. Policy makers and housing experts in those countries have often opted for the provision of completely finished flats in multistorey walk-ups. This has been the main trend in public housing policy in Egypt for the last forty years. Yet, on the other hand, public housing dwellers have been engaged, for many years and through their own initiatives, in informal alteration and extension activities aimed at adapting their dwellings to better suit their needs. This has resulted, not only in an increase of housing accommodation but in improving the socio-economic conditions of families and in changing static housing environments into dynamic multiple_use developments. Understanding this phenomenon is a prerequisite to future interventions in housing. This paper investigates more closely the transformation process though an in_depth analysis of case studies selected in a project in Cairo. It identifies the actors involved and examines their roles in different phases of the transformation process such as the decision making, the financing and the construction phases. Finally, it assesses the costs and benefits of user transformations, and discusses the new roles which could be played by governments and housing professionals in supporting existing self_help processes. The research supports the argument that professional intervention in housing should be based on a careful understanding of the way people have traditionally transformed their environment to improve their own living conditions. The findings could provide planners, designers and policy makers, with new tools in order to formulate feasible and sustainable housing intervention strategies for low income populations.