This paper presents the process and the results of a Research by Design (RbD) investigation on passive techniques to improve the indoor temperature of poor houses in Brazilian hot climates. Poor houses, offering an overheated indoor environment, have been analysed. The paper gives a more detailed description of the in-situ research phase, which informed the hypothesis through the experience with the contacted communities, setting up the pre-requisite: all strategies applied should be effective; low-cost; Do-It-Yourself (DIY) friendly for self-construction. Design and post-design phases, sequentially alternate during the investigation, three times, until the pursuit of viable solutions. Radiant barrier and Tetrapak insulation board solutions presented the best results at the lowest price, for 5€/m2 and 1-2€/m2, respectively. The research presents suitable and validated low-cost materials and technics to be used to shape both thermal and physical spaces in this poor context, showing a possible path to find “the place of architecture in a planet of slums” (Fiori Arantes, Pedro (2008): O lugar da arquitectura num planeta de favelas. Opúsculo, Ed. Dafne. Porto.).
Keywords: poor houses, indoor comfort, DIY thermal improving.