| # | Company name | Role | # of projects |
|---|---|---|---|
| 1 | i3 Consultores | Architect | 6 |
| 2 | Ibergruas | Crane supplier (construction) | 3 |
| 3 | Iberpacc | Real estate agent | 2 |
| 4 | Iberplaco | Internal wall supplier | 2 |
| 5 | Imasatec | Construction company | 0 |
| 6 | Imtech España | MEP engineering | 11 |
| 7 | INASUS | Facade designer | 2 |
| 8 | Independent Architectural Diplomacy | Architect | 1 |
| 9 | Iñigo Ortiz & Enrique León Arquitectos | Architect | 6 |
| 10 | Initec Tecnología, S.A. | Consultancy | 1 |
| 11 | Inmobiliaria Asón S.A. | Real estate agent | 2 |
| 12 | Inmobiliaria Bami | Real estate agent | 0 |
| 13 | Inmobiliaria Chamartin S.A. | Real estate agent | 1 |
| 14 | Inmobiliaria Espacio S. L. | Real estate agent | 19 |
| 15 | Inmobiliaria Marplus S.A. | Real estate agent | 1 |
| 16 | Inmobiliaria Metropolitana Vasco Central S.A. | Real estate agent | 25 |
| 17 | Instituto Universitario de Microgravedad "Ignacio Da Riva" | Wind surveyor | 8 |
| 18 | Isover | Wall insulation supplier | 6 |
| 19 | Iurbentia Promociones Inmobiliarias | Developer | 6 |