| Plumbers Local Union #5 | Related tax-exempt org | Annuity fund | MD | 522124369 |
| Plumbers Local Union #5 | Related tax-exempt org | Labor union | MD | 530067475 |
| Concrete Visions LLC | Related partnership | — | — | — |
| DC Mechanical LLC | Related partnership | — | — | — |
| G&M Services LLC | Related partnership | — | — | — |
| Limbach Company LLC | Related partnership | — | — | — |
| JOHN Joseph Contracting LLC | Related partnership | — | — | — |
| ALL Mechanical & Plumbing LLC | Related partnership | — | — | — |
| H&D Mechanical LLC | Related partnership | — | — | — |
| Systems 3 Service LLC | Related partnership | — | — | — |
| Titan Construction LLC | Related partnership | — | — | — |
| ADJ Sheet Metal INC | Related partnership | — | — | — |
| Bernward Mechanical & Construction | Related partnership | — | — | — |
| Capital Brand Group LLC | Related partnership | — | — | — |
| Enginuity LLC | Related partnership | — | — | — |
| Heritage Mechanical LLC | Related partnership | — | — | — |
| Performance Mechanical LLC | Related partnership | — | — | — |
| Mecco LLC | Related partnership | — | — | — |
| Excel Mechanical Contractors LLC | Related partnership | — | — | — |
| AL Gleeson Electrical | Related taxable corporation/trust | — | — | — |
| American Combustion | Related taxable corporation/trust | — | — | — |
| American Mechanical | Related taxable corporation/trust | — | — | — |
| BPI Mechanical Contractors | Related taxable corporation/trust | — | — | — |
| BECK Plumbing INC | Related taxable corporation/trust | — | — | — |
| Bowers INC We | Related taxable corporation/trust | — | — | — |