Prefab ADUs in the Bay Area
The Bay Area permits more ADUs than any region but Los Angeles — and pays some of the highest rents in the country. Our factory in Lathrop is about an hour from most Bay Area cities: we deliver an all-in prefab ADU — permits, foundation, delivery and installation included — at one price fixed in writing.
Free lot check · zoning, fire & hydrant access · reply with a fixed price
Licensed builder · Our own factory in Lathrop, CA
Real homes we build, start to finish
Quick answer
ADUs in the Bay Area — key facts for 2026
Most Bay Area homeowners can add a detached ADU of at least 800 sq ft under state law, with no city impact fees up to 750 sq ft and no owner-occupancy rule. Bay Modular delivers a factory-built ADU all-in for $124,900–$271,900 — the same price anywhere in California, fixed in writing.
- Can I build an ADU in the Bay Area?
- Yes, on most lots with a house. State law guarantees at least an 800 sq ft detached ADU with 4-ft side and rear setbacks in every city.
- How long does a permit take?
- Cities must approve or deny a complete ADU application within 60 days (Gov. Code §66317).
- What fees apply?
- No city impact fees up to 750 sq ft; school fees only above 500 sq ft. Utility connection fees depend on your lot.
- How much does a prefab ADU cost?
- Bay Modular: $124,900–$271,900 all-in for a rentable ADU, permits and installation included; $75,900 for a Backyard Studio home office.
- How many ADUs does the Bay Area build?
- 4,815 ADU permits in 2025 — 23.5% of all new homes in the nine counties (HCD APR).
- What does an ADU rent for?
- Average asking rent was $3,815 in the San Jose metro and $3,409 in the San Francisco metro in August 2026 (Zillow).
Sources: HCD APR 2025 (Table A2), HCD ADU Handbook (2026), Zillow ZORI Aug 2026, HUD FY2027 FMR. Last reviewed October 2026.
Bay Area in numbers
Bay Area homeowners keep building ADUs
Up 16% since 2021 — and in 2025 almost one in four new homes in the nine counties was an ADU.
ADU permits issued in the Bay Area
Source: California HCD Annual Progress Report data (Table A2), Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano and Sonoma counties, permits issued per year. Percent = ADUs among all housing units permitted that year.
average asking rent, San Jose metro (San Francisco metro $3,409)
Zillow Observed Rent Index, metro, Aug 2026region in California for ADU permits in 2025, after Los Angeles County
HCD APR data, 2025Top cities, 2025
San Jose502 ADUs
Oakland192 ADUs
Fremont188 ADUs
San Francisco171 ADUs
Santa Clara140 ADUs
HCD APR data, permits issued in 2025Can I build in the Bay Area?
Most Bay Area lots with a house can add an ADU
State law sets minimum rights that every city in the Bay Area must honor. Here is what applies on most lots:
Every city must allow at least an 800 sq ft detached ADU, whatever its lot-coverage rules (Gov. Code §66321(b)(3)). All our models fit.
No more than 4 ft from side and rear lot lines; at least 16 ft of height for a detached ADU, 18 ft near transit (§66314(d)(7), §66321(b)(4)).
No parking required within ½ mile of transit, and no replacement parking when a garage is removed (§66322).
Cities can't require you to live on the property; they may require rentals of 30+ days (§66315).
No city impact fees for ADUs up to 750 sq ft (§66311.5); school fees apply only above 500 sq ft (Ed. Code §17620).
The city must approve or deny a complete application within 60 days (§66317).
Each Bay Area city sets its own size, height and design standards on top of state law — for example, San Jose and Sunnyvale allow a detached ADU up to 1,000 sq ft. Open your city page for the details.
Wildland-urban interface and hillside lots (Oakland hills, Saratoga, Marin, Sonoma) add fire-access and defensible-space review.
New ADUs are generally exempt from local rent-control caps (Costa-Hawkins) and from the statewide cap for their first 15 years (Civil Code §1947.12); just-cause eviction rules can still apply. San Francisco, Oakland and San Jose have their own ordinances — see the city pages.
Based on the HCD ADU Handbook (2026) and Gov. Code §§66311.5, 66314, 66315, 66317, 66321, 66322. Not legal advice — local standards differ; see our city pages: San Jose, San Francisco, Oakland, Santa Clara, Fremont, Palo Alto, Saratoga, Sunnyvale, San Mateo guide.
New in 2027: under AB 956 (Chapter 791, Statutes of 2026), from January 1, 2027 state law lets you build two detached ADUs on a lot with a single-family home, and HOA rules can’t block an ADU on a lot zoned to allow one.
Costs & fees in the Bay Area
What an ADU costs in the Bay Area
Same price as anywhere in California. Every model is 750 sq ft or less, so none pays city impact fees under state law; the only school fee — on the 2 Bedroom ADU — is included in the price.
| Model | All-in price | School fee | City impact fee |
|---|---|---|---|
| Backyard Studio120 sq ft · home office or guest studio, not a rentable ADU | $75,900 | $0 | $0 |
| Small Studio256 sq ft | $124,900 | $0 | $0 |
| Large Studio ADU320 sq ft | $154,900 | $0 | $0 |
| 1 Bedroom ADU480 sq ft | $214,900 | $0 | $0 |
| 2 Bedroom ADU640 sq ft | $271,900 | Included | $0 |
Sources: Gov. Code §66311.5; Ed. Code §17620. Comparison is general — every project differs.
Renting in the Bay Area
Renting out an ADU in the Bay Area
average asking rent for all homes in the San Jose metro ($3,409 in the San Francisco metro). HUD's 2027 fair rent for a 2-bedroom is $3,272 in San Jose, $3,697 in San Francisco and $2,805 in Oakland-Fremont.
Zillow Observed Rent Index (all homes, metro), Aug 2026 · HUD FY2027 2-bedroom Fair Market Rent by HUD area. ADU for rental incomeCities may require ADU rentals of 30 days or more (Gov. Code §66315), and many Bay Area cities ban short-term rentals in ADUs — plan on long-term tenants.
New ADUs are generally exempt from local rent-control caps (Costa-Hawkins); San Francisco, Oakland and San Jose have their own ordinances — see the city pages.
A new ADU is exempt from California's statewide rent cap (AB 1482) for 15 years after its certificate of occupancy.
Same money, other options
Yearly income per dollar, before taxes and costs. An ADU wins because you already own the land. Full comparison →
Sources: Civil Code §1947.12; Gov. Code §66315. Comparison: HUD FY2027 2-bedroom Fair Market Rent, San Jose-Sunnyvale-Santa Clara area ($3,272) × 12 ÷ $271,900; U.S. Treasury (Oct 6, 2026); FTSE Nareit (Sep 2026); Zillow ZORI ÷ ZHVI, San Jose metro (Aug 2026); FDIC (Sep 2026). Not legal or investment advice.
Permits in the Bay Area
How your ADU permit works — we handle it
Free lot check
Zoning, fire & flood maps, setbacks, access, sewer and power for your address.
Plans & submittal
Our HCD-approved plans plus your site plan, submitted to your city or county building department.
City review
Your city reviews the plans; we answer every correction for you.
Decision in 60 days
State law requires a decision on a complete application within 60 days. Your ADU is built in our factory meanwhile.
Install & move in
Delivered from our Lathrop factory — about an hour from most Bay Area cities — installed in about a week, inspected, then your Certificate of Occupancy.
* State law: the city must approve or deny a complete application within 60 days (Gov. Code §66317). Every lot differs.
Based on Gov. Code §66317 and the HCD ADU Handbook (2026). Review times vary by city — see our city pages for local details.
Why now
Start your Bay Area ADU with zero risk
Lock in launch pricing, see exactly what you get, and only decide once you have a fixed price for your lot.
All-in from $75,900 — everything included
- Backyard Studio (home office)$75,900All-in · fixed in writing
- Small Studio$124,900All-in · fixed in writing
- Large Studio ADU$154,900All-in · fixed in writing
- 1 Bedroom ADU$214,900All-in · fixed in writing
- 2 Bedroom ADU$271,900All-in · fixed in writing
Zero-risk start
- Free lot check & quoteNo obligation, no credit card.
- One fixed all-in priceDesign, permits, delivery and install — one number.
- HCD-approved plansState approval #1585366, financed and appraised like a home.
- 2-year warrantyOn materials and workmanship.
Visit our factory in Lathrop, CA and walk through a finished ADU.
Bay Area ADU questions
See all of California, open your city: San Jose, San Francisco, Oakland, Santa Clara, Fremont, or call (209) 214-6845.
How much does a prefab ADU cost in the Bay Area?
Bay Modular prices are the same anywhere in California: from $75,900 for a Backyard Studio (home office) and $124,900–$271,900 for a rentable ADU, all-in — design, permits and city fees, foundation, delivery, crane, utility hook-ups and final inspection, fixed in writing after a free lot check.
How many ADUs are built in the Bay Area?
4,815 ADU permits were issued across the nine Bay Area counties in 2025 (HCD APR data) — 23.5% of all new homes. San Jose led with 502, then Oakland 192, Fremont 188, San Francisco 171 and Santa Clara 140.
What does an ADU rent for in the Bay Area?
Average asking rent was $3,815 in the San Jose metro and $3,409 in the San Francisco metro in August 2026 (Zillow). HUD's 2027 fair rent for a 2-bedroom is $3,697 in San Francisco, $3,272 in San Jose and $2,805 in Oakland-Fremont.
How long does a Bay Area ADU permit take?
State law requires cities to approve or deny a complete ADU application within 60 days (Gov. Code §66317). Factory building runs in parallel, and installation on site takes days, not months.
Can I build two ADUs on my lot?
From January 1, 2027, AB 956 lets you build two detached ADUs on a lot with a single-family home, and HOA rules can't block them where zoning allows a single-family home. Today most Bay Area lots can add one detached ADU plus a JADU.
Do you deliver to my Bay Area city?
Yes — we build across all nine Bay Area counties from our factory in Lathrop, about an hour from most Bay Area cities. Send your address for a free lot check.
Free · no obligation
Can you build an ADU on your Bay Area lot?
Send your address. We'll check zoning, fire and flood maps, access and utilities, and send a price fixed in writing — permits included.
HCD-approved plans (#1585366) · 2-year warranty · factory in Lathrop, CA
Sources: California HCD Annual Progress Report data, Table A2 (Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano and Sonoma counties, 2021–2025, updated Oct 2026); Zillow Observed Rent Index, metro areas (Aug 2026); HUD FY2027 Fair Market Rents; HCD ADU Handbook (2026); Gov. Code §§66311.5–66322; Ed. Code §17620; Civil Code §1947.12; AB 956 (Ch. 791, Stats. 2026). General information, not legal or investment advice. Updated October 2026.