An accessory dwelling unit, or ADU, is a self-contained living space located within or on the same property as a principal dwelling. ADUs are typically smaller and more affordable than traditional homes, making them useful for extended family, guests, or rental income while fitting naturally into low- and moderate-density neighborhoods. In Washington, many cities and counties must allow two ADUs on residential lots that permit a single-family home. Everett homeowners should still confirm zoning, setbacks, design standards, parking, utilities, permitting, financing, and construction costs before moving forward. A local real estate professional can help evaluate whether an ADU could complement the property and long-term goals.