Kit Switch is a construction start-up creating modular apartment interiors for building retrofits and conversions, reducing the time, cost, and embodied carbon of multifamily developments. Kit Switch replaces the fragmented, uncertain and time-consuming on-site retrofit process with plug-and-play manufactured products. It manages a digital library of components, such as kitchen kits and bathroom kits, allowing architects to drag-and-drop 3D models and instantly generate layouts and quotes, local manufacturers to produce in parallel of on-site work, and for contractors to install plug-and-play products with a 1 day turnaround on-site instead of weeks of coordination.