Steel Doors 101

Steel Thickness (Levels)

The lower the gauge, the thicker the steel.  Commercial steel doors are typically manufactured in 20, 18, 16 or 14 gauge thicknesses.  Respectively these gauges represent SDI physical performance levels 1-4 for standard, heavy, extra heavy and maximum duty door grades.

Hardware Prep

#161 hardware prep includes a 2-1/8″ diameter bore with 2-3/4″ back-set for standard commercial locks.  Deadbolt prep can be added as a shop modification for an additional charge.

#86 hardware prep includes a 1-1/4″ wide x 8″ tall edge cutout to accept cassette style mortise locks.  Function hole prep for #86 mortise locks can be done in the field or added as a shop modification for an additional charge.

#RPD prep includes internal reinforcement for surface mounted exit device hardware. Function holes and trim prep can be added in the field or as a shop modification for an additional charge.

Galvanneal / Galvanized Steel Doors

Galvanized or galvannealed material is used to reduce corrosion and increase longevity in exterior door applications.  Galvanized steel labeled with the “G” distinctions such as G90 provide a high density zinc coating, but may be more difficult to weld or paint.  A60 and A40 Galvannealed steel offers more of a dull matte finish surface that provides an optimal surface for paint adherence.

STC Sound Resistant Doors

STC sound resistant doors utilize proprietary cores, door components and manufacturing methods to limit the transfer of sound through a steel door opening.  STC ratings for steel doors can range from the mid to high 20’s on standard doors and can reach the mid 50’s in models specifically designed to reduce sound.  A higher STC rating indicates a greater resistance to sound transmission and will usually have a much higher cost than a standard metal door.

Double Egress Doors

Double egress doors are typically used to divide hallways into separate fire corridors.  Double egress doors are pairs of doors that swing in opposite directions to maximize the flow of foot traffic in opposing directions.  Double egress doors typically require surface vertical rod panic exit devices on the push side of both doors, as well as commercial door closers to meet the self-closing and positive latching requirement for fire rated emergency exit doors.

Door Edges (Models)

Model 1 commercial hollow metal doors with the “Full Flush” edge designation include a full height vertical seam at the edges of the door.

Model 2 hollow metal commercial steel doors with the “Seamless” designation include vertical edge seams that have been welded, filled and primed smooth for a seamless finish.

Vision Lites

Vision lites and vision lite kits make it easy to add a window to almost any metal door.  The vision lite is a window frame that simply wraps around a cutout in a steel door. Specialty vision lite frames are available for high security, hurricane ratings and more.  Fire rated doors with glass are available both with and without wire mesh.  Choose from clear, obscure, 2 way mirror, and insulated glass options for non fire rated doors.


Commercial steel louver doors allow air to circulate through a building.  Louvers of almost any size can be added to a commercial steel door.  Fire rated louver doors are restricted to a maximum louver size of 24″ x 24″.  Insect screens, bird screens and security grilles are also available. Louvers can be made from stainless steel or galvanized material for use in harsh climates.

Ballistic / Bullet Resistant Doors

Bullet resistant doors can range in ballistic levels 1-8.  On the lower end of the spectrum a level 1 bullet resistant door has been tested to stop at least three shots from a 9mm bullet.  Level 7 & 8 ballistic doors can resist at least 5 shots from a 5.56mm AR15 rifle or similar.  Level 8 can stop at least 5 shots from an AK-47 firing a 7.62mm rifle bullet.

Tornado Resistant Doors

Tornado resistant doors, also known as FEMA 361 or ICC-500 compliant doors are required in exterior door applications subject to tornadoes. Tornado resistant doors must be made from 14 gauge steel face sheets and include 12″ vertical steel stiffeners spaced no more than 4″ apart.  All tornado resistant doors must use a Securitech concealed or surface mounted multi-point latching system.

Glass Types

Commercial steel doors are available with clear tempered, safety-wire glass, fire-lite ceramic fire glass, Pyran PPF and Kerashield fire rated glass, mirror glass, frosted obscure glass, insulated glass, hurricane impact rated glass, radiation resistant glass and more.

Fire Rated Doors

Fire labels for commercial doors are applied in 20 minute (1/3 hr.), 45 minute (3/4 hr.), 60 minute (1 hr.), 90 minute (1-1/2 hr.) and 180 minute (3 hr.) designations.  20 minute fire doors are typically used in applications where smoke and draft control is needed.  45 minute doors are typically used in openings between corridors.  1 hour fire rated doors are typically required in openings that separate sub divided spaces in the same building. 90 minute doors are typically required at stairwells and elevator shafts.  3 hour fire rated doors are typically used in walls that separate 2 buildings or divide a building into separate fire protection zones.

Double Doors

Inactive doors include strike and flush bolt prep allowing the door to latch at the top and bottom for use as the secondary door in a pair.  Vertical rod exit devices are typically required in applications where both doors must fully operate and function independently.  The use of push plates and pull handles without a positive latching mechanism are only permitted in non fire rated openings.

Hurricane / Impact Doors

Impact and wind resistant doors and hardware are typically required in coastal areas subject to hurricanes and sever windstorms. Miami-Dade County was the first jurisdiction to implement hurricane resistant building standards for doors and frames, followed by others such as the state of Florida Building Code (FBC), Miami-Dade County Building Code, and Texas Department of Insurance (TDI).

Lead Lined Doors

Lead lined doors are typically used in medical imaging applications to reduce the passage of radiation through an opening.  Lead sheets ranging from 1/32″ to 1/4″ are often integrated into doors, frames and hardware.

Embossed Panel Metal Doors

Embossed metal doors typically include a faux panel design, most typically in 1 panel, 2 panel or 6 panel steel door configurations without sacrificing durability, fire or impact ratings.  Due to the manufacturing process, embossed doors are typically available only in common sized.  Custom embossed panel doors are only cost effective when being manufactured in mass quantities.

Core Construction

Polystyrene: High density foam core.  Moderate insulating value.  Standard hollow metal door core for most manufacturers.

Honeycomb: Corrugated honeycomb stiffener with open air space.  Low insulating value.  Provides slightly higher dent resistance than polystyrene.

Polyurethane: Formed in place foam core for maximum insulating value and increased dent resistance.  Typically a made-to-order product for most commercial door manufacturers.

Steel Stiffened: Vertical steel stiffeners are placed inside the door for added strength and durability.  Designed for high frequency severe traffic doors and high impact doors.  Open space is usually filled with mineral fiber insulation to reduce thermal and sound transmission.

Temperature Rise: A full body mineral fiber board core limits the transfer of heat between the exposed and non-exposed sides of a door during a fire.

Stainless Steel Door Types

Stainless steel doors are typically made from either 304 or 316 type stainless steel. Compared to 304 stainless steel, 316 stainless steel includes slightly less chromium, slightly more nickel and about 2% molybdenum to resist corrosion from sea water and chlorides for added resistance to marine grade or harsh environments.  Stainless door alloys bearing the L description such as 304L or 316L have lower carbon variances to reduce weld decay.  Stainless steel doors are most commonly ordered in #4 satin finish but can also be ordered in #8 mirror finish or 2B mill finish.

Integral Lites

Integral lites can be built into any custom hollow metal door.  An integral lite includes a non-removable stop rabbeted into the door during manufacturing with factory sized removable stops supplied for the interior door side.  Integral lites are typically perceived as a higher end and often more visually pleasing option than a vision lite insert.  Hollow metal doors with integral lites are most commonly used in entry door applications.

Steel Dutch Doors

A dutch door allows a door opening to be converted into a service counter on an as needed basis.  Dutch doors are split into a top and bottom section that can operate independently from one another and may include a shelf on one or both sides.