Hollow Metal Doors

Understanding the construction of commercial steel doors.

Commercial Steel doors, otherwise known as hollow metal doors are widely chosen for their durability, cost effectiveness and ability to accept a wide range of commercial door hardware.  Steel doors are fire resistant, readily available and can be prepped for window or louver inserts.  Hollow metal doors can be used for interior or exterior openings and are often used as security doors, emergency exit doors, or as fire doors in stairwells.  Commercial fire rated hollow metal doors are available in a range of steel types, edge construction and core options.

Steel Types & Thickness


  • 18ga. Steel: Heavy Duty (USA Fire Door Standard)
  • 16ga. Steel: Extra Heavy Duty
  • 14ga. Steel: Maximum Duty


  • 16ga. Steel: Heavy Duty (USA Fire Door Standard)
  • 14ga. Steel: Extra Heavy Duty
  • 12ga. Steel: Custom   

Galvanized Steel vs. Hot/Cold Rolled Steel

Cold rolled steel doors are protected from the elements with a rust inhibiting paint/primer that is applied at the factory.  Galvanized or galvannealed steel doors and frames are constructed from zinc coated sheet steel for use in corrosive environments.

Core Construction

Honeycomb: Used in interior or exterior applications with minimal insulation requirements.

Polystyrene: Used in interior or exterior applications where an insulating value is required. (USA Fire Door Standard)

Polyurethane: High insulating properties.  Used in cold climates only.

Steel Stiffened: Includes vertical steel reinforcements inside the door for high traffic or high abuse applications.

Temperature Rise: Typically used in stairwells where a fire rated door is required to resist the transfer of heat through the door. 

Edge Construction

Seamless: In most instances seamless doors are specified for aesthetic reasons only.  The small seam on the door has been filled or welded then sanded and painted.

Edge Seam: The door has a small seam where the sheet metal faced join together. (USA Fire Door Standard)

Hardware Prep Options

161 Cylindrical Lock Prep: Standard hardware prep

86 Mortise Lock Prep: 1-1/4” x 8” large body mortise lock case

Rim Panic Reinforced: Door is prepped with additional steel reinforcement for surface mounted exit devices.  Function holes are not pre-drilled in the door.

Custom Modifications

Vision Lite & Louver Inserts: Windows and louvers can be added in many standard or custom steel door configurations.

Custom sizes & hardware prep: Custom sizes and hardware prep are available.  Custom doors can be fabricated for use on existing frames.

Fire Ratings:

Commercial hollow metal doors can be fire rated from 20 minutes to 3 hours.  Adding a window or a louver to the door may reduce the fire rating.  Fire ratings of commercial hollow metal doors with windows can vary based on the visible glass size.  It is important to consider that a fire rated assembly can only be rated to its weakest component.  If you were to hang a 3 hour door on a 90 minute frame the assembly would only be approved for use in a 90 minute opening.          


SDI 108-10 Selection and Usage Guide for Standard Steel Doors

SDI 112-08 Zinc-Coated (Galvanized/Galvannealed) Steel Doors and Frames

SDI 111-09 Recommended Details for Standard Steel Doors, Frames, Accessories and Related Components

SDI 118-01 Basic Fire Door Requirements