Given the implications of energy use in housing units for global warming, life cycle assessment (LCA) has been used to examine greenhouse gas (GHG) emissions. Although informal settlements, currently known as colonias populares, or barrios, house most of the urban population in Latin America, there is a poor understanding of how people in these communities use energy and contribute to GHG emissions. This investigation provides a comprehensive analysis of resource consumption in Mexico City’s colonia popular, including self-help housing, household energy consumption, and transportation. As there is no spatially specific data on energy use, the author conducted field research in the informal community of Isidro Fabela, founded in the 1960s. Isidro Fabela is an illuminating community that helps understand the energy use of informal settlements at advanced stages of urban consolidation. A mixed-method research approach served to collect empirical data through observations, household surveys, and in-depth interviews. Research sheds light on the efficient and sustainable ways in which families use energy, materials, and resources during self-help construction, and through their daily lives, in their community. The community-based LCA assessment finds that the contribution of Isidro Fabela to GHG emissions is 50% of the average impact in Mexico City. Natural gas or liquefied petroleum gas (LPG) consumption for water heating is the most significant contributor to GHG emissions because families use inefficient heaters. Interestingly, by using public transportation and even walking, residents moderate the contribution of work commutes to GHG emissions. Therefore, climate change policy should enhance low-energy practices in informal settlements, by improving access to energy-efficient technologies and public transportation, to help families contribute further to GHG mitigation in Mexico City and elsewhere in Latin America.