Construction materials are essential for meeting societal needs in urban areas; however, they pose significant challenges for decarbonization, particularly in rapidly growing cities that struggle to meet the needs of all their citizens, such as those in the Global South (GS). This research develops and applies a GIS-based methodology to create an urban material stock map for Lima, Peru, encompassing both nonresidential and residential buildings, with the latter categorized into informal and formal housing. This study combines block-level spatial data with a refined definition of informality that better captures the nuances of reality while acknowledging its limitations, along with an extensive housing typology to calculate the material stocks present in the city. Material intensity (MI) factors were developed for each housing type, allowing for the estimation of material stocks across Lima’s districts. The MI of informal housing is up to 70% less than that of formal housing. The results indicate that informal settlements comprise a substantial share of the housing (50%) and residential stock (31%) in the city. The research also highlights spatial disparities in material accumulation and their correlation with income inequality. This approach provides a replicable framework for other cities in the GS, addressing the urgent need for local data and tailored methodologies to inform sustainable urban planning and decarbonization strategies.