| Ns Elite Construction | Nicole Michele Summers | — | (925) 305 7765 | GC, remodel, ADU | Brentwood · Contra Costa County | — | — |
| Nu Image Painting And Construction | Michael O Reilly | — | (925) 672 7777 | GC, remodel, ADU | Clayton · Contra Costa County | — | — |
| Nugent Constructors INC | James Everett Nugent | — | (925) 683 3712 | GC, remodel, ADU | Danville · Contra Costa County | — | — |
| Nunez General Construction | Juan Jose Nunez | — | (510) 253 5321 | GC, remodel, ADU | San Pablo · Contra Costa County | — | — |
| Nuti | James Edward Nuti | — | (925) 335 6884 | GC, remodel, ADU | Danville · Contra Costa County | — | — |
| Nv Construction LLC | Pariz Mahoma Nunez | — | (510) 236 9111 | GC, remodel, ADU | Richmond · Contra Costa County | — | — |
| Nviro Hardwood Floors INC | Lam Son Nguyen | — | (510) 507 1160 | Other | San Pablo · Contra Costa County | — | — |
| Nwp Heating And Air | Valderrama Cesar | — | (925) 787 7498 | HVAC | Concord · Contra Costa County | — | — |
| Nyswonger Low Voltage | Nyswonger Low Voltage | — | (925) 989 0344 | Other | Brentwood · Contra Costa County | — | — |
| O Bay Construction | Orozco Antonio | — | (925) 864 2066 | GC, remodel, ADU | El Sobrante · Contra Costa County | — | — |
| O C M Developers INC | Williams Obedie | — | (510) 381 0349 | GC, remodel, ADU | Discovery Bay · Contra Costa County | — | — |
| O M B Remodeling & Custom Trim | Bobby Ray Jones | — | (925) 382 0925 | GC, remodel, ADU | Antioch · Contra Costa County | — | — |
| O P Framers INC | Oscar Rene Perez | — | (925) 595 4376 | GC, remodel, ADU | Discovery Bay · Contra Costa County | — | — |
| O S J Electric LLC | Ossamu Jr Sakaguti | — | (925) 788-3178 | Electricians | Lafayette · Contra Costa County | — | — |
| O'brien Contractors | James Christopher O'brien | — | (925) 989 8747 | GC, remodel, ADU | Discovery Bay · Contra Costa County | — | — |
| O'connell Interior Painting | O'connell Interior Painting | — | (510) 926 2360 | Windows, patio, painters | Kensington · Contra Costa County | — | — |
| O'pro Construction INC | Stuart Luo | — | (415) 987 7373 | GC, remodel, ADU | Pittsburg · Contra Costa County | — | — |
| O'reilly Electric INC | Adam Lawrence O'reilly | — | (925) 382 5788 | Electricians | Martinez · Contra Costa County | — | — |
| O'ryan Construction Solutions INC | Richard Jr Gaunt | — | (925) 825 4085 | GC, remodel, ADU | Concord · Contra Costa County | — | — |
| O'sullivan & Son Construction INC | Oliver John O'sullivan | — | (415) 235 5006 | GC, remodel, ADU | San Ramon · Contra Costa County | — | — |
| Oak & Iron Buildworks | Jonathan Andrew Croke | — | (415) 525 6093 | GC, remodel, ADU | San Pablo · Contra Costa County | — | — |
| Oak Construction | Wilfrido Vargas Armenta | info@oakconstruction.com | (510) 806 5642 | GC, remodel, ADU | Richmond · Contra Costa County | — | — |
| Oak Creek Contractors INC | Garry Eugene Burns | — | (510) 603 4622 | GC, remodel, ADU | Danville · Contra Costa County | — | — |
| Oak Grove Tree Care | Rodolfo Duran Ii De Rosas | — | (925) 565 4505 | Tree | Bay Point · Contra Costa County | — | — |
| Oak Knoll Vertical LLC | Robert Walker Jr West | — | (415) 234 0031 | GC, remodel, ADU | Concord · Contra Costa County | — | — |
| Oak Roots Landscape INC | Jose Alberto Enriquez | — | (925) 690 7040 | Windows, patio, painters | Martinez · Contra Costa County | — | — |
| Oakley Heating And Air LLC | Terry Kriag Stone | — | (925) 727 1494 | HVAC | Oakley · Contra Costa County | — | — |
| Oakmount Concrete | Oakmount Concrete | john@smith.com | (925) 577 8992 | Windows, patio, painters | Pittsburg · Contra Costa County | — | — |
| Oakplant Landscaping INC | Felipe Alves Francisco | — | (510) 593 7965 | Windows, patio, painters | Concord · Contra Costa County | — | — |
| Oasis Construction | Kent Lee Vanhole | — | (925) 858 7487 | GC, remodel, ADU | Pleasant Hill · Contra Costa County | — | — |
| Ocean C C Pool & Spa Service & Repairs | Marvin Thamkins Doldol | — | (925) 435 6265 | Pool | Antioch · Contra Costa County | — | — |
| Oceanfront Construction INC | Ricky Jr Pitre | — | (901) 216 0156 | GC, remodel, ADU | Richmond · Contra Costa County | — | — |
| Ochoa Painting | Ochoa Painting | — | (925) 305 1789 | Windows, patio, painters | Pittsburg · Contra Costa County | — | — |
| Ochoa's Art Tile Designing INC | Hector Miguel Ochoa | — | (925) 354 3341 | Other | Pacheco · Contra Costa County | — | — |
| Odeh Electrical & Security INC | Moatasem Bellah Odeh | — | (925) 822 4473 | Electricians | San Ramon · Contra Costa County | — | — |
| Odyssey Builders | Brannan Michael Gary | — | (925) 914 1847 | GC, remodel, ADU | Clayton · Contra Costa County | — | — |
| Office Storage Systems INC | Robert John Brauer | — | (925) 708 3196 | GC, remodel, ADU | Walnut Creek · Contra Costa County | — | — |
| Og Floors INC | Daniel Corona | — | (916) 692 6160 | Other | Richmond · Contra Costa County | — | — |
| Og G&s Paving INC | Jerry Robert Stanley | — | (925) 679 1940 | Other | Oakley · Contra Costa County | — | — |
| Og Pro Construction INC | Ramirez Angel Aguilera | — | (415) 917 7470 | GC, remodel, ADU | Antioch · Contra Costa County | — | — |