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ADU Builders in Diamond Bar, CA

46 builders · ranked by Google rating and review volume · 22 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 Diamond Bar 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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With roughly 55,072 residents at the 2020 Census, Diamond Bar is one of Los Angeles County's established communities. We found 46 ADU builders and contractors that show up for Diamond Bar homeowners on Google Maps, 2 of them based in the city itself. Their average Google rating is 4.7 stars. 20 market themselves specifically as ADU builders, and 1 mention garage conversions. 22 have a matched, active CSLB license shown with a verified badge. The top-rated by our review-weighted score are SouthSTAR Construction, Skilled Home Builders and Hostetler Construction Inc..

Los Angeles leads California in ADU permits. Common projects here include garage conversions on older lots, detached backyard units on deep lots, and hillside sites where access and grading drive the cost.

#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 Diamond Bar · based in Rancho Cucamonga
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#6

Khan Construction Co.

4.9 (37 Google reviews)
✔ CSLB License Verified #700519

5802 Aurora Ave, Jurupa Valley, CA 91752

Serves Diamond Bar · based in Jurupa Valley
Home builderGeneral contractor
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#8

Backyard Estates

4.9 (30 Google reviews)
✔ CSLB License Verified #1076065

2335 W Foothill Blvd #18, Upland, CA 91786

Serves Diamond Bar · based in Upland
Home builder
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#9

Capy Construction

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

Service-area business · Walnut

Serves Diamond Bar · based in Walnut
Remodels & additionsHome builderGeneral contractor
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#20

The ADU Company

5.0 (6 Google reviews)
✔ CSLB License Verified #1118354

504 E Navilla Pl, Covina, CA 91723

Serves Diamond Bar · based in Covina
ADU specialistRemodels & additionsHome builderGeneral contractor
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#24

DMAX Construction

5.0 (4 Google reviews)

621 N Monte Vista Ave, San Dimas, CA 91773

Serves Diamond Bar · based in San Dimas
Remodels & additionsGeneral contractor
CallView profile
#25

The ADU Pro

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

15338 Central Ave, Chino, CA 91710

Serves Diamond Bar · based in Chino
ADU specialistHome builderGeneral contractor
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#27

ADU Experts

5.0 (3 Google reviews)

Service-area business · Azusa

Serves Diamond Bar · based in Azusa
ADU specialistGeneral contractor
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#36

BCM Group Inc

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

9339 Feron Blvd, Rancho Cucamonga, CA 91730

Serves Diamond Bar · based in Rancho Cucamonga
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#39

Apex Construction

3.7 (6 Google reviews)
✔ CSLB License Verified #1020301

Service-area business · La Habra

Serves Diamond Bar · based in La Habra
ADU specialistRemodels & additionsGeneral contractor
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#40

CalHome ADU

1.0 (1 Google reviews)

2540 Fulton Rd, Pomona, CA 91767

Serves Diamond Bar · based in Pomona
ADU specialistGeneral contractor
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#41

JLF ADU

No rating yet (0 Google reviews)
✔ CSLB License Verified #1075968

4716 N Fircroft Ave, Covina, CA 91722

Serves Diamond Bar · based in Covina
ADU specialist
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#44

Ironbridge ADU

No rating yet (0 Google reviews)

Service-area business · Upland

Serves Diamond Bar · based in Upland
ADU specialistPrefab / modularHome builder
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#46

Premier ADU

No rating yet (0 Google reviews)

Service-area business · Upland

Serves Diamond Bar · based in Upland
ADU specialistGeneral contractor
CallWebsiteView profile

Permits and pre-approved plans in Diamond Bar

ADU permits in Diamond Bar 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 Diamond Bar whether it has approved plans you can use. See our pre-approved plans guide and California ADU law summary.

Planning an ADU in Diamond Bar? Start here

Prefab and Modular ADUs in California: Real Costs, Permits and PitfallsHow to Legalize an Unpermitted ADU in California (AB 2533)ADU Rental Income and Property Taxes in California: What to ExpectHow to Choose an ADU Builder in Southern California: 15-Point Checklist

All ADU guides →

Diamond Bar ADU FAQ

How many ADU builders serve Diamond Bar?

Our directory lists 46 ADU builders and contractors that appear for Diamond Bar on Google Maps, including companies based in nearby Los Angeles County communities.

Do I need a permit to build an ADU in Diamond Bar?

Yes. ADUs need a building permit from the City of Diamond Bar, 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 Diamond Bar?

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 Diamond Bar 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 Los Angeles County

Los Angeles 118Long Beach 119Santa Clarita 27Glendale 117Lancaster 12Palmdale 12Pomona 67Torrance 98Pasadena 100Downey 28West Covina 68El Monte 24
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