What Is an ADU?

An Accessory Dwelling Unit (ADU) is a secondary residential structure located on the same lot as a primary single-family home. Common types include:

• Detached ADUs: Standalone structures like backyard cottages.
• Attached ADUs: Extensions connected to the primary home.
• Garage Conversions: Transformed garages now used as livable space.
• Basement Apartments: Finished basements with separate entries and facilities.

ADUs offer flexibility for multi-generational living, rental income, or aging in place—but before you start building, you need to understand your local rules.

Understanding Zoning Laws

Zoning laws vary widely by city, county, and even neighborhood. Here’s what to look for in your jurisdiction:

1. Zoning District Compatibility

ADUs are typically allowed in residential zones, but some municipalities limit them to specific zoning types (e.g., R1, R2). Start by checking your property’s zoning designation via your city or county’s GIS map or planning department.

2. Size and Setback Requirements

Most areas regulate:

• Maximum square footage of the ADU (often a percentage of the main home or a set limit like 800–1,200 sq ft).
• Height restrictions (especially for two-story ADUs).
• Minimum setbacks from property lines, which can affect placement.

3. Occupancy and Use Restrictions

Some jurisdictions require the property owner to live in either the main house or the ADU. Others restrict short-term rentals like Airbnb or limit the number of unrelated occupants.

4. Parking Requirements

Some cities waive parking requirements for ADUs near transit, while others require one off-street space per unit. Always verify current local policies, as these are changing rapidly in response to housing shortages.

Permitting Process: What to Expect

Once you’ve confirmed that an ADU is permitted on your property, you’ll need to obtain the proper permits. Here’s a general overview of the process:

1. Pre-Application Research

Contact your local building or planning department to:

• Confirm zoning compliance
• Ask about recent ADU code changes
• Get a checklist of required documents and fees

2. Design and Documentation

You’ll need detailed plans, including:

• Site plan showing existing and proposed structures
• Floor plans and elevations
• Structural, mechanical, electrical, and plumbing drawings
• Title 24 energy compliance forms (in California and other states)

Working with a designer or architect familiar with ADUs in your area can save significant time and stress here.

3. Submit for Review

Turn in your complete application to the local building department. Some cities now offer online permitting portals. Expect:

• Plan check fees
• Multiple rounds of comments and corrections
• Potential coordination with fire, utility, or health departments

4. Permit Issuance

Once your plans are approved and fees are paid, the building permit will be issued. Construction must follow the approved plans and pass inspections throughout the build.

Tips to Make the Process Smoother

• Talk to your neighbors early: Friendly communication can help avoid complaints or opposition.
• Hire local professionals: Designers and contractors who’ve worked on ADUs in your area know how to avoid common red flags.
• Stay organized: Keep copies of all correspondence, submittals, and approved plans.
• Follow up regularly: Don’t be afraid to politely check in on your application’s status if reviews stall.

Final Thoughts

Navigating local ADU zoning laws and permitting can feel daunting, but it’s a crucial step toward a successful build. With a clear understanding of your local codes and a solid plan, you’ll be well-positioned to create a functional, legal, and valuable addition to your property.

As more cities embrace ADUs to tackle housing shortages, the process is becoming more accessible. Do your research, lean on local expertise, and stay patient—your ADU journey is worth it.

“Zoning” by Nick Youngson via Alpha Stock Images (https://www.picpedia.org/chalkboard/z/zoning.html) is licensed under CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/)