Adding an Accessory Dwelling Unit (ADU) to your property in Marin County can be a smart way to increase your living space, generate rental income, and provide housing for family members or others. But with so many options and local rules, it can feel overwhelming to figure out what’s possible and how to get started. This guide will walk you through the essentials of building an ADU in Marin County in 2026, from choosing the right type to understanding fees and the architectur