How Much Does an ADU Cost in San Jose, CA?
ADU costs in San Jose depend on the type of unit, size, site conditions, and finishes. Below are typical all-in ranges — including construction, design, and permits — based on recent CA market conditions.
Typical cost ranges in San Jose
| Project type | Estimated range |
|---|---|
| Detached ADU (new build) | $200,000–$450,000 |
| Garage conversion | $110,000–$200,000 |
| Design & permitting | $15,000–$40,000 (varies) |
| Utility connections | $5,000–$30,000 (varies) |
These are editorial estimates, not quotes. Actual costs vary significantly by property, scope, and contractor — request multiple quotes before budgeting.
What drives ADU cost in San Jose
- Size: larger units cost more in total but often less per square foot.
- Site conditions: slopes, mature trees, drainage, and access for equipment.
- Utilities: distance to sewer/water/electrical, panel upgrades, or new service.
- Foundation and structure: especially for garage conversions with older slabs.
- Finish level: kitchens and bathrooms are the most expensive rooms per square foot.
- Design and permits: custom design costs more than pre-approved plans where San Jose offers them.
FAQ
How much does an ADU cost in San Jose?
Most detached ADUs in San Jose land in the $200,000–$450,000 range all-in, depending on size, finishes, and site conditions. Garage conversions typically run $110,000–$200,000. These are editorial estimates — get multiple quotes for your specific property.
Do I need a permit to build an ADU in San Jose?
Yes. Every ADU and garage conversion in San Jose requires building permits. The good news: California law requires ministerial (no public hearing) approval for code-compliant ADUs. State law caps review of complete applications at 60 days. San Jose's pre-approved ADU program can cut plan review significantly; custom builds commonly take 3–5 months from design to permit.
How long does it take to build an ADU in San Jose?
Plan for 3–6 months of design and permitting, then 4–8 months of construction for a detached ADU. Garage conversions are usually faster — often 3–5 months of construction once permits are issued.
Can I rent out my ADU in San Jose?
Yes — long-term rentals (30+ days) of ADUs are allowed statewide in California. Short-term rental rules vary by city, so check San Jose's short-term rental ordinance before planning Airbnb-style use.
Ready to compare local pros? See ADU builders in San Jose or garage conversion contractors in San Jose.