Informal housing constructed by informal builders is one of the primary challenges in disaster management, as its residents become more vulnerable to impacts of natural hazards such as hurricanes and earthquakes. When Hurricane Maria hit Puerto Rico, it damaged 1.1 million homes. Since the informal builders in Puerto Rico are involved in designing housing structures but often lack formal training in this area, it is important to understand the analytical processes that engage them in designing houses. Emergent literature has studied informal builders’ local knowledge and learning styles, but there is no information on their design decisions. Design decision is an analytical decision process that uses design methodology to address an existing circumstance (problem) into a desired outcome. Understanding design decisions is critical because it helps identify analytical processes that impede resilience in the design and construction of houses. To address the gap in the literature, this study investigates the design decisions of informal builders using ethnographic interviews with 15 informal builders in three municipalities in Puerto Rico. Through narrative analysis, results show that housing designs were mostly based on structural and architectural considerations, but some participants commonly used analogies and compliance to explain their reasons for the design. Analogies are construction design concepts explained through experiences and compared to each other to create an idea. Compliance is the act of obeying a rule, and in the construction context, refers to the act of fulfilling a command, such as following a blueprint or an engineer’s instruction. While architectural and structural considerations are important for design decisions, analogies can be problematic as they often can include misalignments of architecture and engineering concepts. Since informal builders continue to make design decisions in Puerto Rico, local organizations seeking to address issues of safe housing need to focus on providing training to informal builders that can address and revisit the use of analogies as a method to make design decisions.