Accessory Dwelling Unit (ADU)

What Is an Accessory Dwelling Unit?

An accessory dwelling unit (ADU) is a self-contained living space located on the same property as a single-family home. ADUs have their own entrance, kitchen, bathroom, and sleeping area, and can be occupied by tenants, family members, or used as a home office. They represent one of the fastest-growing segments in residential real estate due to relaxed zoning laws across the country.

Types of ADUs

ADUs come in several forms. Garage conversions transform an existing attached or detached garage into a livable unit — often the most cost-effective approach at $50,000–$150,000. Basement conversions work well in regions with below-grade construction, typically costing $60,000–$120,000. Detached ADUs are standalone structures built in the backyard, ranging from $100,000–$300,000 depending on size and finishes. Internal conversions carve a unit out of existing square footage within the primary home, and prefab or modular ADUs offer faster construction timelines at predictable costs.

Zoning Reforms Driving ADU Growth

California led the charge with AB 68 and subsequent legislation effectively legalizing ADUs statewide by removing parking requirements, reducing setbacks, and preventing HOA bans. Oregon, Washington, and numerous cities across the country have followed suit. These reforms eliminate many of the barriers that historically made ADU construction difficult — from minimum lot sizes to owner-occupancy requirements. Investors should research local ADU ordinances carefully, as rules around size limits, design standards, and rental restrictions vary significantly by jurisdiction.

ADU Investment Strategies

The most straightforward ADU strategy is building one on a property you already own to generate rental income — effectively creating a duplex from a single-family home. House hackers can live in the ADU and rent the main house, or vice versa. More advanced investors target properties with ADU potential, factoring the construction cost and future rental income into their acquisition analysis. In high-rent markets like Los Angeles or Portland, an ADU renting for $1,500–$2,500 per month can deliver a 10–15% return on the construction investment.

Costs, Financing, and Rental Income

Total ADU costs typically range from $100,000 to $300,000 for new detached construction, with garage conversions at the lower end. Financing options include home equity loans (HELOCs), cash-out refinances, construction loans, and specialized ADU loan products offered by some lenders. Rental income potential depends on the local market — in major metros, ADUs can generate $1,200–$3,000 per month. The key calculation is whether the monthly rental income, minus any loan payments and maintenance, produces a positive cash-on-cash return that justifies the construction investment and effort.