| Kyin Construction | Chiou Kyin | — | (510) 508 9912 | GC, remodel, ADU | Orinda · Contra Costa County | — | — |
| Kyle Hansen Painting | Kyle Hansen Painting | — | (925) 899 2189 | Windows, patio, painters | Lafayette · Contra Costa County | — | — |
| Kyle Tile | Kyle Tile | — | (916) 307 3473 | Other | Discovery Bay · Contra Costa County | — | — |
| Kylor Construction INC | Maria Bernadette Ferreira | — | (925) 408 5560 | GC, remodel, ADU | Walnut Creek · Contra Costa County | — | — |
| Kyvos Construction INC | Margaritis Nikolaos | — | (510) 512 8851 | GC, remodel, ADU | Pittsburg · Contra Costa County | — | — |
| Kz Heating And Air Conditioning | Kz Heating And Air Conditioning | — | (415) 815 5371 | HVAC | Antioch · Contra Costa County | — | — |
| Kza-nova Home Remodeling INC | Eladio Rodriguez | — | (510) 680 8974 | GC, remodel, ADU | Richmond · Contra Costa County | — | — |
| L & L Home Remodeling INC | Jose Heriberto Ledesma Palafox | — | (925) 301 6323 | GC, remodel, ADU | Antioch · Contra Costa County | — | — |
| L & L Window Products Corporation | Casto Dominguez | — | (925) 838 0915 | Windows, patio, painters | Danville · Contra Costa County | — | — |
| L A Williams Gutters And Sheetmetal | Leslie Armstrong Williams | — | (510) 851 8661 | Other | El Cerrito · Contra Costa County | — | — |
| L B L Engineering INC | Bennett John Franzel | — | (707) 975 4512 | Other | Pleasant Hill · Contra Costa County | — | — |
| L C Construction | Cosmin Claudiu Lung | — | (510) 303 8439 | GC, remodel, ADU | San Ramon · Contra Costa County | — | — |
| L C G Electrical INC | Guzman Leandro Cordova | — | (408) 605 5872 | Electricians | Brentwood · Contra Costa County | — | — |
| L Columna General Contractor | L Columna General Contractor | — | (925) 698 0813 | GC, remodel, ADU | Concord · Contra Costa County | — | — |
| L D Strobel Co INC | Christopher Michael Foye | — | (925) 686 3241 | Electricians | Concord · Contra Costa County | — | — |
| L E Construction Home Services | Ludin Aroldo Estrada Arroyo | — | (415) 424 8615 | GC, remodel, ADU | San Pablo · Contra Costa County | — | — |
| L G Painting | L G Painting | — | (925) 570 0632 | Windows, patio, painters | Concord · Contra Costa County | — | — |
| L H I Construction | Luigi Greg Barberio | — | (925) 768 2808 | GC, remodel, ADU | Concord · Contra Costa County | — | — |
| L H White General Building Contractor | Lewis Howard White | — | (925) 934 6449 | Electricians | Lafayette · Contra Costa County | — | — |
| L I G Corporation DBA Scharmer Sprinklers & Landscape | Mark Austin Scharmer | — | (925) 934 6958 | Windows, patio, painters | Walnut Creek · Contra Costa County | — | — |
| L K Howard Construction | Lawrence Keith Howard | — | (510) 367 1595 | GC, remodel, ADU | Rodeo · Contra Costa County | — | — |
| L M Preciado Construction | Luis Mario Preciado | — | (925) 351 6165 | GC, remodel, ADU | Martinez · Contra Costa County | — | — |
| L M R Development INC DBA Avalon Builders | Michael John Pennisi | — | (925) 899 4603 | GC, remodel, ADU | Alamo · Contra Costa County | — | — |
| L Q Construction | Lester Aman Quintanilla | — | (510) 708 5368 | GC, remodel, ADU | El Sobrante · Contra Costa County | — | — |
| L R Paulsell Consulting INC L R Paulsell Consulting Engineer | Lloyd Robin Paulsell | — | (510) 787 3037 | Other | Crockett · Contra Costa County | — | — |
| L Schupp | L Schupp | — | (510) 223 8205 | Other | El Sobrante · Contra Costa County | — | — |
| L Spessard Associates | Lyn Paula Spessard | — | (925) 260 3191 | Windows, patio, painters | Antioch · Contra Costa County | — | — |
| L V Plumbing | L V Plumbing | — | (925) 234 6771 | Other | Antioch · Contra Costa County | — | — |
| La Cresta Building Company | David Harold Eckert | — | (510) 333 2150 | GC, remodel, ADU | Orinda · Contra Costa County | — | — |
| La House Care Awei INC | Jilong Jiang | — | (925) 318 0941 | GC, remodel, ADU | Pittsburg · Contra Costa County | — | — |
| La Joya Construction INC | Miguel Angel Cardoso | impallari@gmail.com | (707) 704 8376 | GC, remodel, ADU | Concord · Contra Costa County | — | — |
| La Pointe Company General Builder | Sean Edward La Pointe | — | (925) 683 9331 | GC, remodel, ADU | Concord · Contra Costa County | — | — |
| La Salle Building Company | Jackson Allen Jr Mosher | — | (510) 915 4219 | GC, remodel, ADU | Orinda · Contra Costa County | — | — |
| Labor Unlimited | Labor Unlimited | — | (925) 516 9534 | Electricians | Discovery Bay · Contra Costa County | — | — |
| Labor Unlimited INC | Marcus Jr Noack | — | (925) 516 9534 | Electricians | Discovery Bay · Contra Costa County | — | — |
| Labowitz Construction | Lewis Jr Labowitz | — | (925) 864 3092 | GC, remodel, ADU | Pacheco · Contra Costa County | — | — |
| Lafayette Glass Company | Robert Jeffrey Gould | info@lafayette-glass.com | (925) 284 9510 | Windows, patio, painters | Lafayette · Contra Costa County | — | — |
| Lafayette Tree & Landscape INC | Simone Raphaela Raeth | — | (925) 284 7816 | Windows, patio, painters | Lafayette · Contra Costa County | — | — |
| Lafayette Woodworking | Lafayette Woodworking | — | (925) 932 5954 | GC, remodel, ADU | Concord · Contra Costa County | — | — |
| Lafferty Construction Co | Richard Samuel Lafferty | — | (925) 570 4383 | GC, remodel, ADU | San Ramon · Contra Costa County | — | — |