Yes, you need a permit, even in ADU-friendly states like California, and skipping it is a risk that surfaces at the worst possible times. Unpermitted work gets discovered, typically at a sale or a tax reassessment, and can bring fines and orders to bring the structure up to code. Build it permitted from the start. On title: a permitted ADU generally does not convert your property into a formal multi-unit designation the way adding a true duplex unit would. It usually records as additional square footage or an extra structure rather than turning a single-family record into a two-unit one. Details matter here, including whether the unit has a full kitchen and bathroom, which can affect how it gets classified and valued. We will be honest that ADU rules have been changing quickly, and the specifics vary by city and county and by when you build. Confirm the permitting path and any zoning limits with your local building department before you start, and if the title classification matters for your financing or resale plans, ask a title company or real estate attorney how your specific structure would be recorded. Getting the paperwork right up front is what saves the headaches later.