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 making their design decisions. The article exposes a reconstructive case study on spontaneous growth patterns underlying an unassisted, incremental self-build housing dynamics.