Quick Answer: An ADU (Accessory Dwelling Unit) is a secondary housing unit on a single-family residential lot — a separate, complete living space with its own kitchen, bathroom, and sleeping area. California law (AB 68, SB 13, AB 3182) dramatically simplified ADU permitting starting in 2020 and has continued to expand ADU rights through 2025. In San Jose, a detached ADU can be up to 1,200 sq ft with 4-foot side/rear setbacks. Cost: $150,000-$350,000. Rental income: $2,500-$5,000/month.
ADU Types in San Jose and California 2025
Helpful Resources:
| ADU Type | Description | Max Size | Typical Cost |
|---|---|---|---|
| Detached ADU | Separate structure in backyard or on lot | 1,200 sq ft | $200,000-$400,000 |
| Attached ADU | Connected to main house (addition) | 50% of main house or 1,200 sq ft | $150,000-$300,000 |
| Garage Conversion ADU | Existing garage converted to living space | Per existing garage size | $80,000-$150,000 |
| JADU (Junior ADU) | Interior conversion within existing home | 500 sq ft | $30,000-$80,000 |
Why Build an ADU in San Jose?
- Rental income: San Jose ADUs rent for $2,500-$5,000/month depending on size and location. A 800 sq ft ADU renting for $3,200/month generates $38,400/year — a 10-15% annual return on a $250,000 ADU investment
- Multigenerational living: House aging parents or adult children on the same lot while maintaining privacy and independence
- Home value increase: ADUs add $200,000-$500,000 to San Jose property values (adding rentable square footage in one of the nation’s most expensive housing markets)
- Housing shortage contribution: California is 3.5 million housing units short — ADUs are the state’s primary tool for adding missing middle housing without rezoning
ADU Financing Options in San Jose 2025
- Cash-out refinance: Extract home equity at today’s rates to fund ADU construction
- HELOC (Home Equity Line of Credit): Draw only what you need as construction progresses
- CalHFA ADU Grant: Up to $40,000 grant for pre-construction costs (pre-app meeting, design, soil report). Not available to everyone — limited funds; apply early
- ADU construction loan: Specialized lenders offer construction-to-permanent ADU loans
- Property assessed financing (PACE): On-bill financing through property taxes; high fees, but no upfront credit requirement
Quartz Construction is San Jose’s ADU specialist with 50+ completed ADUs. Learn about ADU construction services. CSLB #1003436 | BBB A+ | 4.9 stars. Call (650) 749-7436.
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"Quartz Construction did an amazing job on our kitchen remodel. The team was professional, on time, and the results exceeded our expectations. Highly recommend to any Bay Area homeowner!"
— Michael T. |
"We hired them for a bathroom remodel in our San Jose home. From permitting to final walkthrough, everything was handled perfectly. The tile work is stunning. 5 stars without hesitation."
— Sarah L. |
"Just finished our ADU garage conversion. The project came in on budget and on schedule — rare in the Bay Area! The rental income already started. Could not be happier with Quartz Construction."
— David R. |
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