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ADU Builders in Ontario, CA

54 builders · ranked by Google rating and review volume · 27 CSLB license verified

★ Featured ADU builder

Featured ADU builder — this spot is open

Put your ADU company at the top of this page, in front of Ontario homeowners who are comparing builders right now. Includes your logo, project photos, a direct call button and a link to your website.

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Located in San Bernardino County, Ontario had a 2020 Census population of about 175,265. We found 54 ADU builders and contractors that show up for Ontario homeowners on Google Maps, 4 of them based in the city itself. Their average Google rating is 4.7 stars. 18 market themselves specifically as ADU builders, and 1 mention garage conversions. 27 have a matched, active CSLB license shown with a verified badge. The top-rated by our review-weighted score are JNC Construction, Skilled Home Builders and Hostetler Construction Inc..

Lots across San Bernardino County are often larger and land costs lower, which makes detached and prefab ADUs attractive. Foothill and mountain areas can face wildfire-zone construction requirements.

#1

JNC Construction

5.0 (143 Google reviews)

9360 Base Line Rd Ste H, Rancho Cucamonga, CA 91701

Serves Ontario · based in Rancho Cucamonga
Remodels & additionsHome builderGeneral contractor
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#4

St Paul Contracting

5.0 (25 Google reviews)
✔ CSLB License Verified #1104071

9650 Business Center Dr Bldg 17, Suite 131, Rancho Cucamonga, CA 91730

Serves Ontario · based in Rancho Cucamonga
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#11

Capy Construction

5.0 (15 Google reviews)
✔ CSLB License Verified #1120565

Service-area business · Walnut

Serves Ontario · based in Walnut
Remodels & additionsHome builderGeneral contractor
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#13

Salem Builders

5.0 (13 Google reviews)

Service-area business · Montclair

Serves Ontario · based in Montclair
Remodels & additionsHome builderGeneral contractor
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#26

H&H Construction

5.0 (4 Google reviews)
✔ CSLB License Verified #868003

120 W Dayton St, Upland, CA 91786

Serves Ontario · based in Upland
Remodels & additionsGeneral contractor
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#28

The ADU Pro

4.7 (15 Google reviews)
✔ CSLB License Verified #1128679

15338 Central Ave, Chino, CA 91710

Serves Ontario · based in Chino
ADU specialistHome builderGeneral contractor
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#31

ADU Experts

5.0 (3 Google reviews)

Service-area business · Azusa

Serves Ontario · based in Azusa
ADU specialistGeneral contractor
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#36

OSHI Construction Inc.

5.0 (2 Google reviews)
✔ CSLB License Verified #990408

10722 Arrow Route Ste 304, Rancho Cucamonga, CA 91730

Serves Ontario · based in Rancho Cucamonga
Remodels & additionsHome builderGeneral contractor
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#37

BAM Construction Inc

5.0 (2 Google reviews)
✔ CSLB License Verified #952311

12345 Mountain Ave Unit N232, Chino, CA 91710

Serves Ontario · based in Chino
Remodels & additionsGeneral contractor
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#38

R&R Improvements

4.6 (10 Google reviews)
✔ CSLB License Verified #1087664

16226 Windcrest Dr, Fontana, CA 92337

Serves Ontario · based in Fontana
Remodels & additionsHome builderGeneral contractor
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#43

BCM Group Inc

4.0 (4 Google reviews)
✔ CSLB License Verified #968356

9339 Feron Blvd, Rancho Cucamonga, CA 91730

Serves Ontario · based in Rancho Cucamonga
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#45

CalHome ADU

1.0 (1 Google reviews)

2540 Fulton Rd, Pomona, CA 91767

Serves Ontario · based in Pomona
ADU specialistGeneral contractor
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#46

Home Masters Int'l

3.9 (38 Google reviews)
✔ CSLB License Verified #1009476

9038 Hellman Ave, Rancho Cucamonga, CA 91730

Serves Ontario · based in Rancho Cucamonga
Remodels & additionsHome builderGeneral contractor
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#51

Premier ADU

No rating yet (0 Google reviews)

Service-area business · Upland

Serves Ontario · based in Upland
ADU specialistGeneral contractor
CallWebsiteView profile
#54

Empower Building Company

No rating yet (0 Google reviews)
✔ CSLB License Verified #1009367

9431 Haven Ave #100, Rancho Cucamonga, CA 91730

Serves Ontario · based in Rancho Cucamonga
Remodels & additionsHome builderGeneral contractor
CallView profile

Permits and pre-approved plans in Ontario

ADU permits in Ontario go through the city's building or planning department. Under AB 1332, every California city and county had to set up a pre-approved ADU plan program by January 1, 2025, so ask Ontario whether it has approved plans you can use. See our pre-approved plans guide and California ADU law summary.

Planning an ADU in Ontario? Start here

Two-Story and Above-Garage ADUs in California: Height Rules, Costs and DesignHow Long Does It Take to Build an ADU in Southern California?Prefab and Modular ADUs in California: Real Costs, Permits and PitfallsADU Rental Income and Property Taxes in California: What to Expect

All ADU guides →

Ontario ADU FAQ

How many ADU builders serve Ontario?

Our directory lists 54 ADU builders and contractors that appear for Ontario on Google Maps, including companies based in nearby San Bernardino County communities.

Do I need a permit to build an ADU in Ontario?

Yes. ADUs need a building permit from the City of Ontario, which must approve or deny a complete application within 60 days under state law. Many cities also offer pre-approved plans that speed up review.

How much does an ADU cost in Ontario?

Most Southern California detached ADUs land around $350 to $550 per square foot all-in, garage conversions around $200 to $350, and JADUs around $50,000 to $150,000. Use our ADU cost estimator and get three itemized bids.

How are Ontario ADU builders ranked here?

By Google rating weighted by the number of reviews, so a 4.9 with 200 reviews ranks above a 5.0 with 3. Featured placements are clearly labeled and don't affect the organic ranking.

Nearby cities in San Bernardino County

San Bernardino 51Fontana 83Rancho Cucamonga 31Victorville 16Rialto 56Hesperia 18Chino 49Upland 27Chino Hills 117Apple Valley 17Redlands 20Highland 8
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