ADU Construction Timeline in San Jose
Timeline is one of the top concerns for homeowners planning an ADU. Unlike a kitchen remodel, ADU construction involves a full design phase, a separate permitting process, and new utility connections — all before construction even begins. Here's a realistic breakdown of what to expect in San Jose's market.
ADU Construction Phase Breakdown
Design & Engineering
Architectural drawings, structural engineering calculations, energy compliance (Title 24), and site plans. Custom designs take longer; pre-approved plans can skip this phase.
Permit Review
City of San Jose plan check and permit review. Standard custom ADUs take 8–16 weeks. Pre-approved standard ADU plans can reduce this to 4–6 weeks via expedited review.
Construction
Site preparation, foundation, framing, roofing, rough MEP, insulation, drywall, finishes, and utility connections. Includes multiple city inspections at key milestones.
Final Inspection & CO
City final inspections, addressing any correction notices, and issuance of the Certificate of Occupancy — the document that legally allows the ADU to be occupied or rented.
Step-by-Step: What Happens During ADU Construction
Site Preparation & Foundation (Weeks 1–4)
Grading, excavation, concrete footings, and slab or raised foundation installation. Soil conditions and foundation type (slab vs. crawlspace) affect this timeline. A soils report may be required for certain sites.
Framing & Roofing (Weeks 3–6)
Wall and roof framing, sheathing, roofing installation, and window and door rough openings. This phase moves quickly with a full crew and good weather.
Rough MEP & Inspections (Weeks 5–10)
Rough-in plumbing, electrical, and HVAC installation inside the walls. City inspections are required before walls can be closed. Scheduling inspections promptly is critical to avoiding delays here.
Insulation, Drywall & Finishes (Weeks 9–16)
Insulation installation, drywall hanging and taping, texture and paint, cabinetry, flooring, tile, and fixture installation. Material lead times matter most during this phase.
Utility Connections (Weeks 14–18)
Connecting the ADU to sewer, water, gas, and electrical service. Utility company scheduling (PG&E for electrical service upgrades) can add 4–8 weeks if a panel upgrade is required at the main house.
Final Inspections & Certificate of Occupancy (Weeks 18–22)
City conducts final building, electrical, plumbing, and mechanical inspections. Any correction notices must be addressed before the Certificate of Occupancy is issued. A dedicated permit coordinator makes this step much smoother.
Tips to Speed Up Your ADU Project
- Use pre-approved standard ADU plans: San Jose offers a library of pre-approved ADU designs that skip standard plan check — cutting permitting from 12+ weeks down to 4–6 weeks.
- Hire a contractor experienced with San Jose permitting: A contractor who has submitted dozens of ADU permits at San Jose's Building Division knows exactly what reviewers check — reducing back-and-forth correction cycles.
- Complete all design documents before submitting: Incomplete submittals are returned and restart the review clock. A complete, well-prepared submittal gets through faster.
- Order long-lead items early: Windows, exterior doors, and specific plumbing fixtures can have 6–12 week lead times. Order during the permit phase so they arrive when framing is complete.
- Proactively schedule inspections: Don't wait until work is done to call for inspections. Schedule 3–5 days in advance so inspectors arrive promptly and work isn't held up waiting.
- Address PG&E early: If an electrical panel upgrade or new service connection is needed, contact PG&E at the start of the permit phase — their scheduling lead times are often 4–8 weeks independent of permit status.
We Know San Jose ADU Permitting Inside and Out
Our team has submitted ADU permits with the City of San Jose more times than we can count. We know which reviewers ask for what, how to prepare a complete submittal on the first pass, and how to get through the process in the shortest legally possible time. See our ADU Construction Service or ADU Permit FAQ for more detail, or contact us for a free consultation.