Steel Doors
MMI hollow metal doors are manufactured with two completely smooth steel face sheets — free of visible welds — using pan-and-lid construction. Their universal handing allows the door to be installed in either left-hand or right-hand openings, a significant advantage on projects where handing requirements vary across the building.
These doors are certified by UL, FM Approvals, and Intertek/Warnock Hersey for up to three hours of fire resistance in a flush, Type F configuration — that is, without vision lites or louvers. When required, the fire-resistance rating can vary depending on the size of any vision lite or louver inserted into the door.
Our fire-rated doors are engineered to provide a very high security level in storage areas and in openings with heavy vehicular or pedestrian traffic. They are built with NP16 panel construction, rated up to 3 hours.
| Steel gage | Opening location | Service duty | Matching frame gage |
| 16 ga (1.3 mm) | Interior and Exterior | Heavy duty | 16 ga and 14 ga steel frames |
| 18 ga (1.0 mm) | Interior and Exterior | Standard duty | 16 ga steel frames |
| Steel type | Opening location | Construction application | |
| Cold-rolled steel (CRS) | Primarily interior | Standard construction conditions | |
| A60 galvannealed | Primarily exterior | Used in high-humidity environments and/or for exposure to the weather | |
Based on environmental conditions, exterior doors are typically galvannealed and interior doors are typically cold-rolled. All fire-rated doors ship with a factory-baked shop primer in gray, ready for field-applied topcoat.