During the Global Passive House Happy Hour this week, Jane Sanders, senior associate and the director of sustainability at Henson Architecture, showcased a single-apartment Passive House retrofit in an 83-unit building located in Brooklyn, New York. While renovations that bring pre-existing buildings up to Passive House level standards are no longer a rarity, retrofitting only a single unit of a large apartment building is exceptional. Sanders talked about the challenges and opportunities that this specific scenario produced, expressing the hope that this approach could become a model for landlords or co-op boards when capital or occupant issues may not allow for all of a building’s units to be renovated at one time instead. The fundamental method she used was to retrofit from the interior, first stripping the walls, ceilings, and floors down to their base structural elements before applying significant amounts of new insulation. The project’s benefits were numerous—much better indoor air quality and insulation from street noise and rowdy neighbors, just to name a couple. This project serves as a great case study for situations in which gradually retrofitting units one-by-one as they became vacant over time is most practical.