Chimney Duplex is a ground-up duplex in West Los Angeles, set behind an existing Spanish-style duplex on a single residential lot. The surrounding neighborhood retains traces of its historic fabric, but these are increasingly dwarfed by extreme mansionization and speculative development that replace modest houses with oversized, generic volumes. Against this backdrop, the project takes a different approach to growth. Its program adds two new rental units to the lot, increasing density without erasing what is already there. Rather than imitating the front building or rejecting it outright, the design integrates and plays with the language of Spanish vernacular (its forms, proportions, and familiar elements), treating them as material to be reinterpreted rather than reproduced. The result is a building that sits in conversation with its older neighbor while proposing something new. Chimney Duplex offers a model for the necessary densification of Los Angeles: neighborly, responsive, and unexpected.