Prefab ADUs in the Inland Empire
The Inland Empire more than doubled its ADU permits since 2021 — and rents above $2,500 a month make a backyard unit pay. 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 the Inland Empire — key facts for 2026
Most Inland Empire 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 Inland Empire?
- 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 and in unincorporated county areas.
- How long does a permit take?
- Cities and counties 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 Inland Empire build?
- 2,455 ADU permits in 2025 — up 136% from 1,042 in 2021 (HCD APR).
- What does an ADU rent for?
- Average asking rent was $2,541 in the Riverside–San Bernardino–Ontario 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.
Inland Empire in numbers
Inland Empire ADU permits more than doubled
From 1,042 in 2021 to 2,455 in 2025 — and ADUs' share of new homes more than doubled, from 6% to 15%.
ADU permits issued in the Inland Empire
Source: California HCD Annual Progress Report data (Table A2), Riverside and San Bernardino counties, permits issued per year. Percent = ADUs among all housing units permitted that year.
more ADU permits in 2025 than in 2021 (1,042 → 2,455)
HCD APR datagross rental yield of an average home in the Riverside metro — an ADU on land you own can do much better
Zillow ZORI × 12 ÷ ZHVI, Aug 2026Top cities, 2025
Fontana240 ADUs
San Bernardino230 ADUs
Riverside208 ADUs
Ontario154 ADUs
Coachella129 ADUs
HCD APR data, permits issued in 2025Can I build in the Inland Empire?
Most Inland Empire lots with a house can add an ADU
State law sets minimum rights that every city in the Inland Empire 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).
Lots in unincorporated areas are permitted by Riverside County or San Bernardino County, not a city — the same state ADU rights apply.
Very high fire hazard severity zones in the foothills and mountains add fire-safety review and can affect siting.
Each city adds its own standards on top of state law. Open your city page or send your address for a free check.
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: Fontana.
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 Inland Empire
What an ADU costs in the Inland Empire
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 Inland Empire
Renting out an ADU in the Inland Empire
average asking rent for all homes in the Riverside–San Bernardino–Ontario metro. HUD's 2027 fair rent for a 2-bedroom in the area is $2,103.
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) — check your city's short-term rental rules before planning a vacation rental.
New ADUs are generally exempt from local rent-control caps (Costa-Hawkins).
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, Riverside-San Bernardino-Ontario area ($2,103) × 12 ÷ $271,900; U.S. Treasury (Oct 6, 2026); FTSE Nareit (Sep 2026); Zillow ZORI ÷ ZHVI, Riverside metro (Aug 2026); FDIC (Sep 2026). Not legal or investment advice.
Permits in the Inland Empire
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 Inland Empire 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.
Inland Empire ADU questions
See all of California, open your city: Fontana, or call (209) 214-6845.
How much does a prefab ADU cost in the Inland Empire?
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 Inland Empire?
2,455 ADU permits were issued in Riverside and San Bernardino counties in 2025 (HCD APR data), up from 1,042 in 2021. Fontana led with 240, then San Bernardino 230, unincorporated Riverside County 227, Riverside 208 and Ontario 154.
What does an ADU rent for in the Inland Empire?
Average asking rent was $2,541 in the Riverside–San Bernardino–Ontario metro in August 2026 (Zillow). HUD's 2027 fair rent for a 2-bedroom in the area is $2,103.
Who issues the permit if I live outside city limits?
In unincorporated areas the county — Riverside County or San Bernardino County — issues the ADU permit, under the same state ADU law.
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 the Inland Empire?
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 Inland Empire 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 (Riverside and San Bernardino 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.