| L C Professional Builders INC | Luis Alfonso Sanchez-Ceja | — | (707) 294 5852 | GC, remodel, ADU | Napa · Napa County | — | — |
| L.a. Custom Pools & Spas Inc. | L.a. Custom Pools & Spas Inc. | lacustompoolsandspas@gmail.com | (888) 457-5377 | Pool | Yucaipa · Napa County | — | — |
| Laboratory By Design INC | Robert Hilary Jr Kaltreider | — | (707) 252 8218 | Other | Napa · Napa County | — | — |
| Landgrebe Lath & Plastering INC | Mark Steven Landgrebe | — | (707) 322 7453 | Other | Napa · Napa County | — | — |
| Lang Specialty Pumps LLC | David Paul Lang | — | (707) 299 8066 | Other | Napa · Napa County | — | — |
| Langhoff Masonry INC | John Edward Langhoff | — | (707) 944 1310 | Other | Yountville · Napa County | — | — |
| Laponza Plumbing INC | Angelo Jr Laponza | — | (707) 312 0547 | Other | Napa · Napa County | — | — |
| Larry Ellis INC DBA Ellis Construction Company | Larry Meier Ellis | — | (707) 255 2551 | GC, remodel, ADU | Napa · Napa County | — | — |
| Larsen Construction | Guy Phillip Larsen | — | (707) 815 6911 | GC, remodel, ADU | Angwin · Napa County | — | — |
| Larson & Co Commercial Painting | Jesse Patrick Larson | — | (707) 332 0845 | Windows, patio, painters | Napa · Napa County | — | — |
| Larson Bros Painting | Jesse Patrick Larson | info@larsonbrospainting.com | (707) 332 0845 | Windows, patio, painters | Napa · Napa County | — | — |
| Lavorico Construction | Joseph Ralph Lavorico | — | (707) 363 6597 | GC, remodel, ADU | Napa · Napa County | — | — |
| Lawncrafters | Cortes Eduardo | lawncrafters.jax@gmail.com | (707) 235 4461 | Windows, patio, painters | Yountville · Napa County | — | — |
| Leal Landscaping | Leal Landscaping | — | (707) 363 6671 | Windows, patio, painters | Napa · Napa County | — | — |
| Leggett Construction INC | Harold M Leggett | — | (707) 494 4409 | GC, remodel, ADU | Napa · Napa County | — | — |
| Levanta Ge | David Matthew Bejar | — | (707) 287 1954 | Other | Napa · Napa County | — | — |
| Level On The Level Custom Builder | Jasper Theodore Filiss | — | (707) 225 5353 | GC, remodel, ADU | Napa · Napa County | — | — |
| Lh Heating And Air | Lh Heating And Air | — | (707) 363 3547 | HVAC | Napa · Napa County | — | — |
| Livewire Electric | Justin Lipatan Small | — | (707) 225 1685 | Electricians | Napa · Napa County | — | — |
| Ljr Builders INC | Robert Bradley Branstad | %20enquiries@ljrbuilders.com | (510) 330 2232 | GC, remodel, ADU | Calistoga · Napa County | — | — |
| Lou Penning Landscapes INC | Benjamin Noah Penning | hello@penninglandscapes.com | (707) 255 8129 | Windows, patio, painters | Napa · Napa County | — | — |
| Lowrey Custom Innovations | Lowrey Custom Innovations | — | (707) 864 5717 | GC, remodel, ADU | Napa · Napa County | — | — |
| Lug Electric INC | Shane Thomas Boardman | — | (707) 718 8438 | Electricians | Napa · Napa County | — | — |
| Luke Construction Corp | Jason Christopher Luke | — | (707) 253 9374 | GC, remodel, ADU | Napa · Napa County | — | — |
| Lumen's Electric | Jason Williams Saunby | — | (415) 305 6673 | Electricians | Napa · Napa County | — | — |
| Luna Painting | Luna Painting | — | (707) 235 1643 | Windows, patio, painters | Napa · Napa County | — | — |
| Lw Construction | Wenona Jean Garside | — | (415) 884 2360 | GC, remodel, ADU | American Canyon · Napa County | — | — |
| M C M Construction | Marc Jameson Cuslidge | — | (707) 721 2387 | GC, remodel, ADU | Napa · Napa County | — | — |
| M G Drywall | M G Drywall | — | (707) 461 5097 | Other | St Helena · Napa County | — | — |
| M H Building INC | Mychael Thomas Holloran | info@mhbuilding.com | (707) 815 1188 | GC, remodel, ADU | Napa · Napa County | — | — |
| M L R Construction Services | Michael Leonard Rode | info@mlrconstructionservices.com | (707) 738 0995 | GC, remodel, ADU | Napa · Napa County | — | — |
| M M A Roofing | Alfredo Virgilio Mora | — | (707) 934 5349 | Other roofers | Napa · Napa County | — | — |
| M M Construction | Leroy Larry Maestas | — | (707) 342 5858 | Other | American Canyon · Napa County | — | — |
| M S B Construction INC | Justin Christopher Jones | — | (707) 337 6436 | GC, remodel, ADU | Napa · Napa County | — | — |
| M3 General Engineering INC | Keith Burdell Murdock | — | (707) 480 4848 | Other | Napa · Napa County | — | — |
| Mabry Construction INC | William John Mabry | — | (707) 258 9663 | GC, remodel, ADU | Napa · Napa County | — | — |
| Madrigal Painting | Madrigal Painting | — | (707) 287 6810 | Windows, patio, painters | Napa · Napa County | — | — |
| Magana Construction | Felipe De Jesus Magana | — | (707) 287 5452 | GC, remodel, ADU | Napa · Napa County | — | — |
| Maib Construction Company INC | Casey William Maib | — | (707) 339 8589 | GC, remodel, ADU | Napa · Napa County | — | — |
| Main Street Electric | Richard Alan Sciutto | — | (707) 963 2122 | Electricians | St Helena · Napa County | — | — |