ADU Construction projects are significant investments that benefit from careful up-front planning. Homeowners who make key decisions before signing a contract end up with better outcomes, fewer change orders, and less stress during construction.
Define Your Scope Before Getting Quotes
California’s ADU law has changed dramatically since 2020. Cities that previously blocked ADUs on procedural grounds now have limited ability to do so. This means homeowners who were told ‘no’ a few years ago may now be eligible. We’ve built ADUs across the Bay Area and Sacramento and know which loopholes cities sometimes try to use — and how to address them. The process takes longer than most other construction projects, but the outcome — rental income, multigenerational housing, or an increase in property value — is consistently worth it. Before reaching out to contractors, spend time defining exactly what you want. The more specific your scope, the more accurately contractors can quote — and the less likely you are to face change orders once work begins.
How the Process Works
A typical adu construction project follows this sequence:
- Feasibility Review — We assess your lot, setbacks, existing structure, utility connections, and zoning rules. We tell you what's buildable before you spend money on design.
- Design & Plans — We develop construction documents for permit submittal. Floor plan, elevations, sections, and all required engineering.
- Permit Submittal & Approval — We submit to the building department, manage plan check comments, and obtain approved permits. This typically takes 4–12 weeks depending on jurisdiction.
- Construction — Foundation, framing, MEP rough-in, insulation, drywall, finish. We coordinate all trades and keep you updated weekly.
- Final Inspection & Handoff — City final inspection, utility connections, and punch list completion. You get the keys to a fully permitted, livable unit.
Setting a Realistic Budget
ADU costs in the Bay Area are among the highest in the country, driven by land costs, permit fees, and labor. That said, the rental income potential consistently exceeds the carrying cost of a construction loan — making most Bay Area ADU projects financially sound. Build in a contingency of 10–15 % on older Bay Area homes where wall conditions cannot be fully assessed until work starts.
Typical cost ranges:
- JADU (Junior ADU, within existing space): $40,000–$100,000
- Garage conversion (full ADU): $120,000–$220,000
- Attached ADU addition: $160,000–$300,000
- Detached ADU (500–800 sq ft): $180,000–$320,000
- Detached ADU (800–1,200 sq ft): $260,000–$450,000
- ADU design and permits (no construction): $15,000–$40,000
Choosing a Contractor
Verify CSLB licence status at CSLB.ca.gov. Ask for a written, itemised scope — not just a total price. Get proof of general liability and workers’ compensation insurance. Ask who your point of contact will be during construction. Ask how the contractor handles unexpected conditions inside walls.
Ready to Start?
IronNest Construction provides free in-home estimates for adu construction projects throughout the Bay Area and Sacramento. We provide written scopes, fixed-price proposals, and clear timelines. CSLB Licenced #1130134.