| # | Company name | Role | # of projects |
|---|---|---|---|
| 1 | I. O. Christensen | MEP engineering | 1 |
| 2 | I.A. Naman + Associates, Inc. | MEP engineering | 45 |
| 3 | I.C. Thomasson Associates, Inc. | MEP engineering | 22 |
| 4 | I.M. Robbins | MEP engineering | 57 |
| 5 | Ian Banham and Associates | MEP engineering | 74 |
| 6 | IBC Engineering Services, Inc. | MEP engineering | 1 |
| 7 | IBG Ingenieurbüro Glaab GmbH | MEP engineering | 1 |
| 8 | IC IngenieurConsult | MEP engineering | 1 |
| 9 | Icade Arcoba | MEP engineering | 1 |
| 10 | Icofluides | MEP engineering | 2 |
| 11 | ICOR Associates, LLC | MEP engineering | 6 |
| 12 | IG Tech GmbH | MEP engineering | 2 |
| 13 | IGAH Ing.-Ges. Abels-Habicht mbH | MEP engineering | 1 |
| 14 | IGK Ingeniergemeinschaft Kruck | MEP engineering | 2 |
| 15 | IHS Intelligent House Solutions GmbH & Co. KG | MEP engineering | 2 |
| 16 | Imec Ltd. | MEP engineering | 0 |
| 17 | IMEK VVS Rådgivande Ingenjörer AB | MEP engineering | 2 |
| 18 | Implicit Engineering Ltd. | MEP engineering | 1 |
| 19 | Imtech España | MEP engineering | 11 |
| 20 | Indoor Quality Solutions, Inc. | MEP engineering | 1 |