What are ADU Laws?
ADU laws are local, state, or federal regulations that govern the construction, use, and rental of accessory dwelling units (ADUs) on residential properties. These laws determine where ADUs can be built, what size they can be, who can live in them, and how they can be used.
ADU laws vary significantly by jurisdiction and typically cover zoning requirements, building codes, parking mandates, setback distances, maximum square footage, and occupancy restrictions. They’re designed to balance the need for more housing with neighborhood character and infrastructure concerns.
How do ADU Laws Work?
ADU laws work by establishing a framework of rules that property owners must follow when adding a secondary living unit to their property. These regulations start at the state level, where governments may pass legislation encouraging or mandating cities to allow ADUs.
Local municipalities then create specific ordinances that detail the requirements. For example, California’s statewide ADU laws require cities to permit ADUs but allow local governments to set standards for size, setbacks, and design. Property owners must apply for permits and ensure their ADU complies with all applicable codes before construction.
Many jurisdictions have streamlined their ADU approval processes in recent years, reducing fees and eliminating certain requirements like parking to encourage development.
Real-World Application of ADU Laws in Real Estate
In real estate transactions, ADU laws directly impact property values and development potential. A property in an area with permissive ADU laws may command a higher price because buyers recognize the opportunity to add rental income or multigenerational housing.
Real estate investors analyze ADU laws when evaluating potential purchases, calculating how much additional income an ADU could generate. In Portland, Oregon, where ADU laws were relaxed in 2010, thousands of homeowners have added units, creating additional housing supply and increasing property values.
Agents must understand local ADU regulations to advise clients accurately about what’s possible on a given property and what permits or variances might be required.
How ADU Laws are Used
Property owners use ADU laws as a guide for what they can legally build on their land. Before starting an ADU project, homeowners typically review local ordinances to determine size limits, placement requirements, and whether owner-occupancy is required.
Developers and contractors reference ADU laws during the design phase to ensure compliance and avoid costly modifications later. They check setback requirements, height restrictions, and whether the ADU must match the primary dwelling’s architectural style.
City planners use ADU laws as a tool for increasing housing density without changing neighborhood character. By allowing ADUs in single-family zones, they can add housing units while maintaining the appearance of traditional residential areas.
In Other Words
Simply put, ADU laws are the rules that tell you what kind of extra living space you can add to your property. Think of them as the guidebook that determines whether you can build a backyard cottage, convert your garage into an apartment, or add a basement suite—and exactly how you need to do it.
These laws answer questions like: How big can it be? How close to the property line? Does it need its own parking? Can you rent it out? The answers depend entirely on where your property is located.
