Prefab ADUs in Orange County
In Orange County, more than one in three new homes is now an ADU — and fair rent for a 2-bedroom tops $3,000 a month. We deliver an all-in prefab ADU from our Lathrop factory — permits, foundation, delivery and installation included — at one price fixed in writing.
Free lot check · zoning, fire & hydrant access · reply with a fixed price
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Quick answer
ADUs in Orange County — key facts for 2026
Most Orange County 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 Orange County?
- 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). Coastal-zone lots may also need a coastal permit.
- 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 Orange County build?
- 2,310 ADU permits in 2025 — 38.5% of all new homes in the county (HCD APR).
- What does an ADU rent for?
- Average asking rent was $2,941 in the Los Angeles–Long Beach–Anaheim metro in August 2026 (Zillow); HUD's 2027 fair rent for a 2-bedroom in Orange County is $3,057.
Sources: HCD APR 2025 (Table A2), HCD ADU Handbook (2026), Zillow ZORI Aug 2026, HUD FY2027 FMR. Last reviewed October 2026.
Orange County in numbers
Orange County ADU permits grow every year
Up 82% since 2021 — and ADUs' share of new homes doubled, from 18% to 38.5%.
ADU permits issued in Orange County
Source: California HCD Annual Progress Report data (Table A2), Orange County, permits issued per year. Percent = ADUs among all housing units permitted that year.
of all new homes permitted in Orange County in 2025 were ADUs — up from 18% in 2021
HCD APR dataHUD's 2027 fair rent for a 2-bedroom in the Santa Ana-Anaheim-Irvine area
HUD FY2027 Fair Market RentsTop cities, 2025
Garden Grove434 ADUs
Anaheim266 ADUs
Santa Ana258 ADUs
Westminster215 ADUs
Fullerton168 ADUs
HCD APR data, permits issued in 2025Can I build in Orange County?
Most Orange County lots with a house can add an ADU
State law sets minimum rights that every city in Orange County 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).
Many Orange County homes sit in HOAs. HOAs can't ban ADUs where zoning allows a single-family home (Civil Code §4751), though reasonable rules may apply.
Lots in the Coastal Zone may need a coastal development permit or waiver in addition to the building permit — we check this for your address.
Each city adds its own standards on top of state law — for example, Garden Grove and Westminster offer city pre-approved ADU plans. Open your city page for the details.
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: Garden Grove, Santa Ana, Westminster.
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 Orange County
What an ADU costs in Orange County
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 Orange County
Renting out an ADU in Orange County
average asking rent for all homes in the Los Angeles–Long Beach–Anaheim metro. HUD's 2027 fair rent for a 2-bedroom in the Santa Ana-Anaheim-Irvine area is $3,057.
Zillow Observed Rent Index (all homes, metro), Aug 2026 · HUD FY2027 2-bedroom Fair Market Rent. ADU for rental incomeCities may require ADU rentals of 30 days or more (Gov. Code §66315), and many Orange County cities restrict short-term rentals — plan on long-term tenants.
New ADUs are generally exempt from local rent-control caps (Costa-Hawkins); check your city page for local rules.
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, Santa Ana-Anaheim-Irvine area ($3,057) × 12 ÷ $271,900; U.S. Treasury (Oct 6, 2026); FTSE Nareit (Sep 2026); Zillow ZORI ÷ ZHVI, Los Angeles–Anaheim metro (Aug 2026); FDIC (Sep 2026). Not legal or investment advice.
Permits in Orange County
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 and 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 Orange County 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.
Orange County ADU questions
See all of California, open your city: Garden Grove, Santa Ana, Westminster, or call (209) 214-6845.
How much does a prefab ADU cost in Orange County?
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 Orange County?
2,310 ADU permits were issued in Orange County in 2025 (HCD APR data) — 38.5% of all new homes. Garden Grove led with 434, then Anaheim 266, Santa Ana 258, Westminster 215 and Fullerton 168.
What does an ADU rent for in Orange County?
Average asking rent was $2,941 in the Los Angeles–Long Beach–Anaheim metro in August 2026 (Zillow). HUD's 2027 fair rent for a 2-bedroom in the Santa Ana-Anaheim-Irvine area is $3,057.
Can my HOA stop me from building an ADU?
No — where zoning allows a single-family home, an HOA can't prohibit an ADU (Civil Code §4751), though it can apply reasonable rules. From 2027, AB 956 extends this to a second detached ADU.
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.
Do you deliver to Orange County?
Yes — we build across California from our factory in Lathrop. Send your address for a free lot check.
Free · no obligation
Can you build an ADU on your Orange County 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 (Orange County, 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.