| One At A Time Fine Woodwork | Patrick Stephen Kadyk | — | (415) 260 3320 | GC, remodel, ADU | Guerneville · Sonoma County | — | — |
| One Way Plumbing INC | Jennifer Anne Birkenes | — | (707) 537 1308 | Other | Santa Rosa · Sonoma County | — | — |
| One World Construction | Brandon Stacey Eufusia | — | (707) 332 5295 | GC, remodel, ADU | Sebastopol · Sonoma County | — | — |
| Ontop Weather Roofing INC | Martinez Pablo | — | (707) 327 9013 | Other roofers | Sebastopol · Sonoma County | — | — |
| Onyx Concrete Company LLC | Diaz Alejandro Vencez | — | (707) 696 9288 | Other | Santa Rosa · Sonoma County | — | — |
| Optemo Hydronics | Optemo Hydronics | — | (707) 292 3400 | HVAC | Santa Rosa · Sonoma County | — | — |
| Optima Landscaping INC | Mendoza Yriberto | — | (707) 280 4126 | Windows, patio, painters | Santa Rosa · Sonoma County | — | — |
| Oracle Consulting INC | David Harvey Harris | — | (415) 744 4045 | GC, remodel, ADU | Santa Rosa · Sonoma County | — | — |
| Organic Metal Construction Corp | Mayra T Gonzalez | — | (510) 274 3819 | Other | Sonoma · Sonoma County | — | — |
| Oria Plumbing | Juan Carlos Oria Cruz | — | (707) 331 8847 | Other | Rohnert Park · Sonoma County | — | — |
| Orion Homes Incorporated | Jason Orion Gooch | — | (707) 535 6851 | GC, remodel, ADU | Petaluma · Sonoma County | — | — |
| Ornelas Construction And Remodeling INC | Delgado Jorge Ornelas | — | (707) 328 1310 | Other roofers | Santa Rosa · Sonoma County | — | — |
| Ortiz & Son's Construction | Elias Vieyra | — | (707) 494 5834 | GC, remodel, ADU | Windsor · Sonoma County | — | — |
| Ortiz Construction | Adan Arenas Ortiz | interested@domainmarket.com | (707) 293 8220 | GC, remodel, ADU | Santa Rosa · Sonoma County | — | — |
| Ortiz Custom Builders INC | Ortiz Montoya Graciano | — | (707) 703 2409 | GC, remodel, ADU | Santa Rosa · Sonoma County | — | — |
| Ortiz Electric | Luis Ignacio Ortiz | — | (707) 908 7190 | Electricians | Glen Ellen · Sonoma County | — | — |
| Osbaldo Construction INC | Willy Osbaldo Perez Santiago | — | (707) 696 7030 | GC, remodel, ADU | Rohnert Park · Sonoma County | — | — |
| Osprey Electric | Joey Clark Reineck | — | (707) 239 9677 | Electricians | Windsor · Sonoma County | — | — |
| Osrodz Construction Services | Luis Ismael Osorio | — | (415) 812 4421 | GC, remodel, ADU | Rohnert Park · Sonoma County | — | — |
| Ostrand Construction | Andrew Christopher Ostrand | — | (707) 292 1540 | GC, remodel, ADU | Rohnert Park · Sonoma County | — | — |
| Ots General Contractors | Ots Hannes | — | (415) 505 4267 | GC, remodel, ADU | Petaluma · Sonoma County | — | — |
| Outdoor Environments | Outdoor Environments | — | (707) 795 0605 | Windows, patio, painters | Cotati · Sonoma County | — | — |
| Outlander Construction INC | Graham Colin Robertson | — | (415) 328 7890 | GC, remodel, ADU | Cotati · Sonoma County | — | — |
| Outside The Box Design & Drafting Services LLC | Seth Edward Gilley | — | (707) 495 8950 | GC, remodel, ADU | Santa Rosa · Sonoma County | — | — |
| Over And Under Construction INC | Dylan James Brucker | — | (707) 303 6889 | Other | Santa Rosa · Sonoma County | — | — |
| Overhead Door Co Of Santa Rosa INC | William Alan Cullumber | — | (707) 542 4949 | Other | Santa Rosa · Sonoma County | — | — |
| Overton Homes | Overton Homes | — | (707) 778 6869 | GC, remodel, ADU | Petaluma · Sonoma County | — | — |
| Owings Design Build | Owings Design Build | — | (707) 287 2983 | GC, remodel, ADU | Sonoma · Sonoma County | — | — |
| Ox Landscape Services | Guadalupe Omar Morales Villa | — | (707) 508 8926 | Windows, patio, painters | Santa Rosa · Sonoma County | — | — |
| P & L Specialties | Lynn Edwin Jr Barr | — | (707) 573 3141 | GC, remodel, ADU | Santa Rosa · Sonoma County | — | — |
| P B George INC | Bradley Thomas Leach | — | (707) 763 4422 | Windows, patio, painters | Camp Meeker · Sonoma County | — | — |
| P B Renovators INC | Philip Allen Bilski | — | (707) 696 4848 | GC, remodel, ADU | Santa Rosa · Sonoma County | — | — |
| P Barboza Painting | P Barboza Painting | — | (707) 888 2452 | Windows, patio, painters | Santa Rosa · Sonoma County | — | — |
| P C S Specialties | P C S Specialties | — | (707) 486 1806 | Pool | Santa Rosa · Sonoma County | — | — |
| P D M Landscape | Paul Desiderio Martinez | office@pdmlandscape.com | (707) 938 1196 | Windows, patio, painters | Glen Ellen · Sonoma County | — | — |
| P E Landscaping | P E Landscaping | — | (707) 849 8979 | Windows, patio, painters | Windsor · Sonoma County | — | — |
| P J Brosnan | P J Brosnan | — | (650) 619 4493 | GC, remodel, ADU | Santa Rosa · Sonoma County | — | — |
| P J M Yard Maintenance INC | Garcia Ayala Ricardo | — | (707) 792 2200 | Windows, patio, painters | Santa Rosa · Sonoma County | — | — |
| P K T Construction | Patrick Karlin Taylor | — | (415) 368 2497 | GC, remodel, ADU | Santa Rosa · Sonoma County | — | — |
| P V Tile Company INC | Paul Brian Vyenielo | — | (707) 823 8816 | Other | Sebastopol · Sonoma County | — | — |