In many developing countries, a large part of the urban population lives in selfbuilt houses located in informal settlements. Due to the basic methods and materials used in self-construction, most houses are only one or two stories high. As a consequence, these informal settlements tend to expand rapidly outward, occupying the safest areas frst and later expanding into areas that are less suitable for construction because of steep slopes or a high risk of foods, landslides or earthquakes. This is precisely what has occurred in Bucaramanga, Colombia, the case study for the present research. The construction of multi-story buildings is a potential solution to this problem, by reducing the extension of informal settlements. The present study reviews existing technical solutions for constructing low-cost foor slabs, one of the most critical aspects in the construction of a house, and presents a multiple-criteria decision-making method for use in prioritizing the alternatives, taking into consideration social, environmental and economic factors. These criteria for choosing between the diferent foor slabs also take into consideration the opinion of the inhabitants of the area, gathered through a survey administered to 772 families in 26 of Bucaramanga’s informal settlements.