What "substantially complete" actually means
Builders typically flag the build as "substantially complete" when the ADU is safe to occupy and only minor cosmetic and punch items remain. SnapADU's complete construction guide treats the final inspections, cleaning, and certificate of occupancy as a discrete closeout phase ranging from days to weeks depending on city inspector availability. That's your signal to begin the final inspection sequence — but you're not done yet.
Final city inspections
California cities run a series of final inspections — building, electrical, plumbing, mechanical, and (in some jurisdictions) planning. These are scheduled in sequence and typically completed across one to two weeks. Each may produce a short correction list that the builder addresses before re-inspection.
Common late-stage issues:
- Egress window heights or sill measurements out of code
- GFCI/AFCI outlet placement in kitchens and baths
- Smoke and CO detector placement, count, and interconnection
- Stairwell clearance and handrail height
- Address numbers visible from the street
- Water heater seismic strapping (California)
- HVAC condensate drainage and clearance
Inspector backlogs are one of the seven most common ADU delay drivers SnapADU flags. A re-inspection cycle in a high-volume California market can add a full week to your completion date.
The certificate of occupancy (CO)
Once all final inspections pass, the city issues a certificate of occupancy (sometimes called a "final" or "C of O"). This is the legal document that says the ADU may be lived in. Don't move yourself or a tenant in before it lands. Homeowners insurance coverage and liability protection both hinge on it, and unpermitted occupancy can trigger code enforcement.
The punch list
Your builder will hand off a punch list of remaining cosmetic and minor functional items. Walk the ADU with the project manager and compare against the original scope. Things to look for:
- Paint touch-ups, drywall dings, scuffs on cabinets and trim
- Door and drawer alignment
- Caulking gaps in kitchens and bathrooms
- Missing hardware, light bulbs, switch plates
- Cleanliness of windows, mirrors, glass shower doors
- HVAC airflow at every register; thermostat function
- Hot water arrival times at the farthest fixture
- Outlet polarity (test every outlet)
- Smoke and CO alarms operate when test button is pressed
Withhold the final 5–10% of the contract payment until the punch list is closed. This is standard practice and your strongest leverage. Pay this final draw promptly once items are signed off — slow approval on a completed punch list damages relationships unnecessarily.
Warranties and handover documents
Your builder should hand over a binder (or digital folder) containing:
- Manufacturer warranties for all appliances, HVAC, water heater, windows, and roofing
- Builder workmanship warranty — typically 1 year, sometimes 2
- Structural warranty — 10 years is industry standard in California
- Title 24 / HERS certificates of compliance (California)
- Maintenance schedule for HVAC (filter changes, biannual service), water heater (annual flush), and exterior
- Subcontractor contact list for repairs and warranty calls
- As-built drawings reflecting any field changes from the permitted set
Re-walk the punch list at the 11-month mark. Most builder workmanship warranties expire at 12 months, and you want any latent issues — paint cracking at corners, doors sticking after seasonal movement, HVAC airflow imbalances — addressed inside the warranty window.
Utility account setup
California ADUs can share utilities with the main home or have separate meters; both are legal under state law. Shared utilities simplify things — there are no new accounts to open. Separate meters require coordinating with PG&E, SDG&E, SCE, or your local utility, plus water and sewer. Allow 1–2 weeks for setup, and request meter installation before the final inspection if separate meters are part of the design — utility companies have their own backlog and you don't want to be waiting on them after the city has already issued your CO.
If you're renting the ADU
Long-term rental is permitted statewide in California; short-term rentals (Airbnb, VRBO) are restricted or banned in many cities, so verify before assuming it's an option. For long-term rental:
- List on Zillow Rental Manager, Apartments.com, or work with a local agent. ADU rent expectations vary widely: Riverside County $1,400–$2,400/mo, Ventura $1,600–$3,000/mo, Orange County $1,700–$3,200/mo, Los Angeles County $1,800–$3,500/mo (Dynamic Quality Builders, 2026).
- Photograph thoroughly while the unit is staged or empty — these photos work for both rental marketing and future appraisal documentation.
- Run background and credit checks on prospective tenants. California has specific limitations on which information you can request and use.
- Use a lease your real estate attorney has reviewed. California-specific requirements (rent control notices in covered cities, security deposit caps, mandatory disclosures) are easy to miss in generic templates.
- Walk the unit with the tenant on move-in and document condition in writing with photos.
- Add a landlord-required rider to your homeowners insurance, or a separate landlord policy. Standard homeowners coverage doesn't extend to tenant occupancy.
- If you're financing on an ADU-aware loan that factored projected rental income, save the signed lease — your lender may request it.
If a family member is moving in
Take a moment. You did this. Most homeowners spend a year thinking about an ADU, six months designing and permitting it, and another six to nine building it. The day someone you love sleeps there for the first time is worth pausing for.
What comes next
Your ADU is built, occupied, and (hopefully) generating rental income or housing family. Three follow-ups worth scheduling:
- Property tax notice. The county assessor will re-appraise after the CO is issued. In California, SB 1164 (2025) provides a 15-year property tax exemption on new ADUs — confirm your county is applying it.
- 11-month warranty walk. Re-inspect everything and submit any warranty items in writing before month 12.
- Appraisal documentation. Keep your final cost breakdown, photos, lease (if rented), and rent receipts. Lenders and appraisers will want them for any future refinance or sale.
Looking back at the whole journey? Return to the process overview or run the numbers on the addition you didn't build with our ROI calculator.