18 open house international Vol 34, No.4, December 2009 Growth Patterns in Incremental... INTRODUCTION The urgency to eliminate homelessness and sub- standard housing in Latin America and the Caribbean persists. The United Nations (UN- Habitat, 2007) predicts the continuous slum forma- tion throughout Africa, the Middle East, Latin America and Asia towards two billion slum dwellers by 2030. The development challenge in Chile comprises the eradication of 533 slums accommo- dating 28.578 homeless households (Arís et al., 2007). The improvement of current support models for participatory design and decision-making tasks is essential to rise to this challenge. Today, there are new approaches involving, for e.g. game-like tools for community workshops (Lee, 2008) or constraint- based reasoning (Donath and González, 2006) that may provoke a useful paradigm shift in this domain. Innovation in participatory housing plan- ning demands the development of time and cost- effective customization new mechanisms. In Chile, dweller participation has been substantially increased over the last seven years, mainly through the implementation of a new project-based funding scheme supported by the nationwide Housing Solidary Fund. However, local governmental strate- gies on participatory housing planning still fail to recognize diversity and complexity embedded in self-managed housing processes (Turner. 1972; 1999). The provision of low-income housing can- not be longer understood as the serial manufactur- ing of a repetitive and monotonous finished prod- uct (Aravena, 2004), but as a dynamic system involving physical and social components over time. Several initiatives have followed the incre- mental transformation and community-driven approach, like Habraken (1972; 1981) and the SAR-Method, which supported modular prefabrica- tion of housing components, community participa- tion in the decision-making process, and dwellers' individual identity rescue, as early in as the late 1960s throughout the 1970s. Although such approach served of great inspiration, its social and constructive complexity impeded a wider diffusion across Latin America and the Caribbean. Nevertheless, the idea of increasing dweller's par- ticipation into the planning and building process, as well as her/his responsibility for procuring and upgrading the own living space, both remain today. That has been demonstrated in several research works, like the review of diverse conditions promot- ing informal settlements (Coccato and Pelli, 2003), Rodrigo García Alvarado, Dirk Donath & Luis Felipe González Böhme Abstract Over the past three decades, a small community of eighty-four Chilean low-income families has built and improved their home incrementally, without any technical assistance, showing an impressive performance. A six square meters bathroom on a serviced plot of land with individual connection to potable water, sewerage, electricity and access roads, worked as a starting point back in 1974. However particular their rationale may seem, the individual history of their housing process reveals some general regularities in occurrence and duration of self-build activities, as well as size and allocation of the domestic spaces. A small random sample of fifteen households was selected to tell the story and explain the whys, hows, and whens of an ever-evolving housing process. Semi-structured interviews and building surveys were both combined to reconstruct the sequence of states of each housing process, with the awareness of the characteristic imprecision of oral information transfer. Alternative states were explored by constraint programming methods and spatial qualitative reasoning. Considering the hard constraints over the site morphology and services allocation, the results of the exploration stress how extraordinary lucid and intuitive the surveyed families are when mak- ing their design decisions. The article exposes a reconstructive case study on spontaneous growth patterns underlying an unassisted, incremental self-build housing dynamics. Keywords: Incremental Self-Build Housing, Spontaneous Growth Patterns, Housing Transformation, Site-And- Services Scheme, Constraint Programming. GROWTH PATTERNS IN INCREMENTAL SELF-BUILD HOUSING IN CHILE