Planning and Designing Your ADU

Assess Your Property

Before diving into design, evaluate whether your property is suitable for an ADU. Consider:

• Lot size and configuration
• Existing structures and their placement
• Access points for construction and future use
• Utility connections and potential upgrades needed
• Topography and drainage patterns
• Trees and landscaping that may be affected

In California, most single-family residential properties qualify for at least one ADU, but physical constraints may limit your options.

Research Local Regulations

While California has statewide ADU laws, local jurisdictions may have additional requirements. Research:

• Zoning regulations specific to your area
• Maximum size allowances (typically up to 1,200 sq ft in California)
• Height restrictions and setback requirements
• Parking requirements (often waived near transit in California)
• Design review processes if applicable
• Impact and connection fees

Contact your local planning department or check their website for ADU-specific guidance.

Determine Your ADU Type

California allows several types of ADUs. Consider which is best for your property:

Detached ADU

A standalone structure separate from the main house. Offers maximum privacy but may require more extensive utility connections.

Attached ADU

Connected to the main house but with separate entrance. Often easier for utility connections and may be more cost-effective.

Conversion ADU

Created by converting existing space like a garage or basement. Often the most affordable option with simplified permitting in California.

Junior ADU (JADU)

Up to 500 sq ft, created within the walls of the main house. May have simplified requirements and lower costs.

California law now allows both an ADU and a JADU on many single-family properties, potentially creating three units on one lot.

Establish Your Budget

Develop a realistic budget for your ADU project. In California, costs typically range:

• Conversion ADU: $100,000 - $200,000
• Attached ADU: $200,000 - $300,000
• Detached ADU: $250,000 - $400,000+

Your budget should include:

• Design and architectural fees
• Permitting costs
• Site preparation
• Construction costs
• Utility connections
• Finishes and fixtures
• Landscaping
• Contingency fund (typically 10-15%)

California offers several financing options, including the CalHFA ADU Grant Program, which provides up to $40,000 in pre-development funding.

Design Your ADU

Work with professionals to design an ADU that meets your needs and complies with regulations:

• Hire an architect or designer with ADU experience
• Consider prefab or modular options for potential cost savings
• Focus on space-efficient design for smaller footprints
• Incorporate California-specific considerations like earthquake safety
• Plan for energy efficiency to meet California's Title 24 requirements
• Consider solar readiness or installation (often required for new construction in California)

Obtain Permits

Navigate the permitting process for your ADU:

• Submit plans to your local building department
• Prepare for plan check corrections and revisions
• Budget for permit fees (varies by jurisdiction)
• Understand the timeline (California law requires streamlined approval for compliant ADUs)

Under California law, compliant ADU applications must receive ministerial approval (without discretionary review) within 60 days in most cases.

Select a Contractor

Choose a qualified contractor for your ADU project:

• Look for contractors with specific ADU experience
• Verify licenses and insurance
• Check references and past projects
• Get multiple bids to compare
• Ensure they're familiar with California building codes

Consider contractors who specialize in the type of ADU you're building (conversion, prefab, custom-built, etc.).