ADU & Garage Conversion
Guide & Cost Breakdown

An Accessory Dwelling Unit (ADU) is a secondary housing unit on a single-family property — either a garage conversion, a new detached structure, a basement conversion, or an addition to the main home. California's landmark ADU legislation (AB 68, AB 2221, SB 9) has dramatically streamlined approvals, making ADU construction one of the most financially compelling projects available to California homeowners.

A well-built ADU in Southern California generates $1,500–$3,500/month in rental income, adds $150,000–$300,000 to property value, and often pays for itself in 4–7 years. With housing demand at record levels, ADUs are increasingly treated as essential infrastructure.

Why Build an ADU?

• Rental Income: $1,500–$3,500/month in most Southern California markets — one of the best cash-on-cash returns available.
• Property Value: ADUs add $150,000–$300,000+ to appraised value in high-demand areas.
• Multi-Generational Living: House family members (parents, adult children) on the same property with independence for everyone.
• Streamlined Approvals: California law now requires ministerial (no public hearing) approval for most ADUs within 60 days.
• No Parking Requirements: ADUs within ½ mile of transit have no parking replacement requirements — even if you convert your garage.

Types of ADU Projects

Garage Conversion ADU ($60,000–$130,000): Converting an existing attached or detached garage into a fully permitted dwelling unit. Most cost-effective ADU type since the structure already exists. Includes electrical, plumbing, HVAC, insulation, drywall, kitchen, bathroom, and exterior compliance.

Detached New Construction ADU ($150,000–$300,000): Building a brand new structure in the backyard. Maximum flexibility in design and size. Requires full foundation, framing, MEP, and exterior work.

Attached Addition ADU ($100,000–$200,000): Adding a new unit attached to the main house, typically over a garage or as a ground-floor addition. Shares one wall with the main structure.

Junior ADU / JADU ($25,000–$60,000): Converting existing interior space (bedroom, basement) into a studio unit. Limited to 500 sq ft. Must share a wall with main house. Less expensive but also less rental income potential.

1. Start with a Feasibility Assessment

Before spending money on design, have a contractor assess your lot for ADU feasibility — setbacks, utility access, soil conditions, HOA restrictions, and local overlay zones. Some lots have constraints that affect cost significantly.

2. California ADU Laws Favor You

Under current law, your city must approve a compliant ADU application within 60 days. They cannot require design review, public hearings, or additional parking for most ADU types. Know your rights — some cities still try to add restrictions.

3. Design for Rental Appeal

If renting the ADU, design for what renters want: full kitchen, in-unit laundry hookups, private entrance, good natural light, and adequate storage. A well-designed ADU commands $300–$600/month more than a basic conversion.

4. Understand Utility Connection Options

ADUs can share utilities with the main house (less expensive, simpler) or have separate meters (more expensive but better for rentals and future sale as separate unit). Discuss both options with your contractor and utility company.

5. Budget for the Full Project

Design fees ($5,000–$15,000), permits ($5,000–$15,000), and utility connections ($5,000–$20,000) are in addition to construction costs. A realistic total budget includes all soft costs.