The Colorado Units in Santa Monica is a detached structure with two new Accessory Dwelling Units (ADU) stacked on top of each other in the rear of an existing multifamily zoned lot. The new project maximizes the use of the property providing a total of 6 apartments for rent adding to the housing stock in the City within walking distance to work, stores, park and social amenities. The two new apartments are designed with individual access from the side street giving identity, individuality and a sense of ownership to the residents of each on a tight lot that had the additional challenge of keeping the existing parking footprint facing the alley. A screen element is designed to provide privacy from the street while allowing light and ventilation. Each ADU unit is a 3 bed-2bath flat with a large main room with a kitchen for shared accommodation or for a family. The new building is a simple sculpted cube that allows a flexible open court between the old and the new structure designed to be accessed as an amenity for all residents and can also be exclusively rented with the new garden unit. Both units are designed to encourage passive sustainability with plenty of light, natural ventilation, deep recessed windows in thick insulated walls and will be net zero energy.