ADU Additions & Garage Conversions in Contra Costa County
DevCo Building Enterprises converts garages, expands existing structures, and builds above-garage ADU additions across Contra Costa and Alameda Counties. Garage-to-ADU conversions typically cost $80,000 to $180,000 - 30 to 50 percent less than ground-up ADU builds. All projects are fully permitted; DevCo manages the complete permit process from application to final inspection. Call (925) 448-2123 for a free site assessment.
If you already have a detached garage, a workshop, an older structure on your property, or a first-floor footprint large enough to add a second story, you may have the most affordable path to a permitted ADU sitting right on your lot. DevCo specializes in these conversion and addition projects - leveraging your existing structure to add rental income, family housing, or resale value at a significantly lower cost than starting from scratch.
ADU Addition Types DevCo Builds
Garage Conversion ADU: What the Process Looks Like
Free site assessment: DevCo reviews garage structure, ceiling height, condition, setbacks, and utility connections
Design: structural and architectural plans prepared for permit submittal
Permit application: DevCo submits to the relevant city building department
Plan check: typically 6 to 12 weeks in Contra Costa cities
Construction: structural work, insulation, electrical, plumbing rough-in, drywall, finishes
Final inspections: city inspector confirms code compliance
Certificate of Occupancy: unit is legally rentable
In our Berkeley and San Leandro garage conversion projects (see portfolio at devco.llc/portfolio), the consistent theme is that homeowners are surprised by how livable and complete a converted garage can be when the process is done right. The key is proper insulation, ceiling height, natural light, and utility connections from the start.
Frequently Asked Questions
Yes. State ADU law allows garage conversions throughout California. DevCo assesses your specific garage before quoting - ceiling height, structural condition, and setback compliance are the key variables.
California ADU law prohibits cities from requiring replacement parking for garage conversions in most circumstances. You may lose covered parking, but replacement spaces cannot be mandated by the city. Check with DevCo about your specific situation.
Yes. The CalHFA ADU Grant Program (up to $40,000) applies to ADU additions and conversions, not only ground-up builds. Eligibility requires owner-occupancy and income qualification. Visit calhfa.ca.gov/adu for current program details.
The /adu-construction page covers ground-up detached ADU builds from scratch. This page covers converting or expanding existing structures - garages, workshops, or above-garage additions. Both result in a fully permitted ADU; the difference is the starting point and cost.
Get a Free Garage Conversion or ADU Addition Estimate
Serving Concord, Walnut Creek, Martinez, Lafayette, Orinda, Pleasant Hill, Clayton, Oakland, Berkeley, and surrounding communities.
Call (925) 448-2123 or visit devco.llc/contact.