Although the full time-frame for a project depends on the size, there are two major phases for an ADU project: the design phase and the construction phase. The design phase includes creating the site plan, floor plans, architectural drawings, and everything needed by the city or local jurisdiction to approve the project. The design phase takes an average of 60-90 days. The construction phase can start once your local jurisdiction approves the project and permits are approved. Depending on the size and complexity, it can take anywhere from 30 days to 180 days for your ADU construction project to be completed. For example, converting an existing garage into a dwelling unit can be done relatively quickly. However, building a new freestanding 1200 square ft two storied structure will require more time.