ADU CITIES Contractor Directory

ADU Contractors in Ontario, CA — License-Verified Contractors

Every contractor below holds an active California license with an office of record in Ontario, verified against CSLB public data as of November 6, 2026: general builders — A (General Engineering) and B (General Building), the classifications that can build an ADU — and the licensed trades ADU construction uses, C-10 Electrical, C-36 Plumbing and C-5 Framing & Rough Carpentry. Listings are alphabetical; the featured builder is labeled, never ranked.

ADU rules — setbacks, size limits, parking, and fees — are set by the local jurisdiction and change often. Before you hire, read the ADU permit process guide and the Southern California ADU cost guide, and verify any license free at CSLB.

★ FEATURED

Mars Construction Industries Corp

ADU Cities' own design-build team

CSLB #1138550 · A · B · C-36 · C-20

Building ADUs across Los Angeles, Orange, Riverside, San Bernardino, San Diego & Ventura counties

Call 888.627.1131View profile →

498 license-verified contractors based in Ontario — page 4 of 10

Data source: CSLB public records as of November 6, 2026 · Verify any license at CSLB