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Commercial Hollow Metal Doors

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Commercial Hollow Metal Doors

A hollow metal door is a type of commercial steel door. The door construction is typically made from heavy duty 18 gauge steel sheets designed for industrial and heavy traffic use. Other lighter duty hollow metal doors are constructed from thinner 20 gauge steel sheets, while extreme heavy duty hollow metal doors are designed with thicker 16 gauge steel sheets. The typical door thickness of a commercial hollow metal door is 1-3/4". The most common misconception is that hollow metal doors are not insulated and are nothing but a metal shell of a door. This is furthest from the truth. Within the steel sheets that make up the outer shell of the hollow metal door, is an insulated core. The most common core type is a polystyrene core. While other core types include honeycomb, polyurethane or a steel stiffened core. Each core provides different benefits and are used in specific applications. The steel sheets of higher quality hollow metal doors are zinc coated by a hot dipping process. These hollow metal doors are known as galvanized or galvannealed hollow metal doors. The proper standards for zinc coating hollow metal doors are the ASTM A 924 / A 924M and ASTM A 653 / A 653M, set forth by Steel Door Institute. Galvannealed hollow metal doors are sought after since the hot dipping zinc heat process the steel sheets are exposed to creates entirely new layer of zinc iron alloy. The benefits of the galvannealed coating allows paint to adhere to the metal door's surface without of any kind of paint pretreatment. Also, the coating is dense making the steel door more resistant to abrasions such as dings or dents. Lastly, the galvannealed coating makes the steel door easier to weld to, making it easier for reinforcements or accessories requiring welding of the steel door.

We only provide hollow metal commercial doors that meet the Steel Door Institute's guidelines as well as the National Association of Architectural Metal Manufacturers. Our hollow metal doors are manufactured in the USA. We offer WHI Warnock Hersey Intertek fire labels on our doors.

Hollow Metal Door Types

Flush Hollow Metal Doors
Hollow metal doors come in a variety of exterior steel sheet designs. The most common hollow metal door is the flush design. A flush hollow metal door is simply a hollow metal door with smooth surface. There are no panel designs, or embossed lines on the door surface. Flush hollow metal doors are considered the "classic" hollow metal door look. They can be found on fire doors in all commercial buildings.

Louvered Hollow Metal Doors
Some hollow metal doors are used in electrical or control rooms. These rooms are often very warm since they house electrical equipment. As a result these hollow metal doors have louvered vents installed on them. These door louvers provide ventilation for the room. Hollow metal doors with louvers are very common in any type of commercial building utility room or storeroom.

Vision Lite Hollow Metal Doors
Another very common hollow metal door design is the vision lite hollow metal door. These hollow metal doors have a glass window installed on them known as a vision lite. The vision lite window provides a number of functions. The most obvious being that it improves the sight or visibility for a person operating the door. The person is able to see what is on the other side of the door. Another benefit is that vision lites can help bring natural light into any room or facility. Vision lite hollow metal doors are very popular in stairwell doors, classroom doors, office doors, and other applications where visibility is a must.

Paneled Hollow Metal Doors
Other hollow metal door designs include the 2 panel, 4 panel, and 6 panel hollow metal door types. These hollow metal doors feature elegant embossed panel designs on the surface of the door. By nature the elegant look of the paneled hollow metal doors is often marketed to hotel doors, motel doors, or even some residential doors. Paneled hollow metal doors offer the best of both worlds; an elegant look coupled with commercial grade duty and reliability versus that of a wood door.

Hollow Metal Door Core Types

When it comes to core types of any commercial hollow metal door it is always best to understand what the R or U values mean first. Simply put, the R value is a measurement of the resistance of the door's core to heat flow. In other words, the higher the R value, the better the door's core is at insulating the commercial building and improving it's energy efficiency. The U value is a measurement of how much heat is lost or gained from the door's core. A lower U value would indicate that the door is well insulated. Another important measurement to understand is the STC rating or Sound Transmission Class rating. As you can guess the STC rating is all about sound. Essentially it is a standardized way of measuring on average how much sound is stopped by the door's core. The higher the STC rating the more "quiet" the door is in regards to outside noise penetrating through. Now that we understand that, let's investigate the various hollow metal door core types.

Polystyrene Core Hollow Metal Doors
The majority of all commercial hollow metal doors are constructed with a polystyrene core. The polystyrene core is essentially a type of foam core that is sandwiched between the two steel sheets of the door. It carries many benefits. For one it enhances the structure of the hollow metal door, while also reducing the weight. It also bonds to the steel sheets very well helping to provide dimensional stability as well as structural integrity. Hollow metal doors with polystyrene core doors are often used on both interior or exterior building applications as they have an R and U value, which is a measurement of insulation. Typical polystyrene core hollow metal doors feature an R value of approximately 6.40 to 7.12 and a U value range of approximately 0.13 to 0.16. Most polystyrene core hollow metal doors have an STC rating of around 25.

Honeycomb Core Hollow Metal Doors
Hollow metal doors with a honeycomb core are not as popular as polystyrene core hollow metal doors. The honeycomb core is essentially constructed of a pattern of cardboard which looks similar to the pattern of a beehive. This honeycomb core is sandwiched between the two steel sheets of the door. Unlike the polystyrene foam core which fills the inside of the door completely, the honeycomb core structure has dead air space in between each honeycomb. This makes it a poor insulating door in comparison to the polystyrene core hollow metal door. Still, there are applications where honeycomb doors can be utilized such as rooms or entries where insulation is not required. In most cases however, honeycomb hollow metal doors are often found in applications where cost must remain low. Typical honeycomb core hollow metal doors feature an R value range of 2.40 to 2.94, a U value range of 0.31 to 0.34, and an STC rating of 35.

Polyurethane Core Hollow Metal Doors
Hollow metal doors with a polyurethane core are somewhat rare and only utilized in specific applications requiring excessive insulation. The polyurethane core offers better R and U values than polystyrene core hollow metal doors. Typical polyurethane hollow metal doors are exterior doors in extremely cold weather.

Steel Stiffened Core Hollow Metal Doors
Steel stiffened hollow metal doors are primarily used for door applications with extremely abusive traffic. The doors are constructed with steel ribs sandwiched between the two steel sheets of the door. This heavy duty reinforcements makes steel stiffened hollow metal doors the most physically robust doors in comparison to it's counterparts; the polystyrene core and honeycomb core doors. Steel stiffened hollow metal doors are often used in commercial buildings where the increased strength of the door is needed, and sound reduction or insulation is not necessary.

Temperature Rise Hollow Metal Doors
Temperature rise hollow metal doors or mineral core doors, are used for applications requiring heat reduction. The door is constructed with a special mineral fiber board that is sandwiched between the two sheets of the door. Temperature rise doors are very useful in commercial buildings in case of a fire. If a fire did occur, the temperature rise hollow metal door would not transmit as much heat as the other hollow metal door types. The mineral fiber board core has properties that help reduce the heat.

Hollow Metal Door Gauges

The door gauge refers to the thickness of the steel door sheets that make up the hollow metal door. Since hollow steel doors are some of the most versatile door types around (can be used as pass through doors, security doors, storeroom doors, etc) it is important to specify the door gauge so that the proper door can be used for a given application. Hollow metal doors range from 14 to 20 gauge. The lower the door gauge the thicker the door face. The most popular and standard hollow metal door gauge is 18 gauge. However if your door is severely abused or you need a heavier duty door then 14 gauge or 16 gauge would be used. 20 gauge is the thinnest of all thicknesses and are not utilized in commercial applications. 20 gauge is often used in residential home applications, however even then an 18 gauge door is preferred, since 20 gauge doors often dent very easy due to their thin metal face. Also, 20 gauge metal is very difficult to weld, if your application requires any type of welding. The standard hollow metal door frame is 16 gauge. The chart below shows the door gauge and thickness of steel frames for hollow metal doors.

Galvannealed vs. Galvanized Hollow Metal Doors

Galvannealed steel is the process of coating steel with zinc on both sides, through the continuous hot-dip process. As soon as the steel leaves the coating bath, the molten zinc coated steel goes through a heat treatment process which converts the entire coating to a zinc iron alloy.
Galvanized steel is the process of coating steel with zinc through the hot-dip process. Unlike the galvannealed process however, galvanized steel features a much thicker zinc coating, causing issues with pain adhesion.
Both processes create a level of zinc on top of the base metal which makes them resistant to corrosion. However, the galvannealed steel is preferred for hollow metal doors since the thinner zinc coating can accept paint without any type of pretreatment. Other benefits of galvannealed steel vs galvanized steel include:
  • A galvannealed coating can be welded much easier than a galvanized coating
  • The galvannealed coating is harder than the thicker galvanized coating, making it more resistant to scratches.
  • The galvannealed coating is less reactive than the galvanized coating, so it's coating does not have to be as thick in order to provide the same amount of rust protection.
Galvannealed hollow metal doors are prime painted with a special rust inhibiting primer. Galvannealed hollow metal doors are often specified for exterior door applications, or in areas near the water where it is more humid and moist. The galvanneal coating itself, can be specified for hollow metal doors as either A40 or A60. A40 is the most minimum recommended gavanneal coating. A60 is the industry recommended standard of galvanneal coating. It is not recommended to exceed the A60 level of galvanneal coating, as it will begin to reduce the paint adhesion.

Hollow Metal Door Components

A commercial hollow metal door can be customized to meet virtually any door application. The below illustration depicts the basic components that make up a standard hollow metal door.

Hollow Metal Door Face:
The outer surface of the hollow metal door. The face is made of steel and is primed to prevent rust.

Hollow Metal Steel Door Frame:
The frame is manufactured from 16 gauge steel. Depending on the door application, a hollow metal door will either have a drywall frame, masonry/exterior frame, or a welded frame.

Hollow Metal Door Frame Head:
The top portion of the hollow metal door frame. Standard hollow metal door frame heads are 2" while specialty frame heads are 4".

Hollow Metal Door Frame Hinge Jamb:
The portion of the hollow metal door frame that is prepped for hinges.

Hollow Metal Door Frame Strike Jamb:
The portion of the hollow metal door frame that is prepped for the cylindrical lock's strike plate.

Hollow Metal Door Insulated Core:
The interior portion of the hollow metal door. This is the space between the two exterior steel sheets that make up the hollow metal door. Hollow metal door cores are often polystyrene, honeycomb, or even polyurethane, depending on your application.

Vision Glass Lite:
This is essentially a glass window installed on the hollow metal door. The vision glass lite provides visibility for pedestrians entering or exiting the door, while also providing natural light into the room.

This is a key or thumbturn style lock with a heavy duty bolt. When locked, the lock's bolt slides into the door frame, providing extra security.

Cylindrical Lock:
This is a lever style door lock and is the most commonly used lock with hollow metal doors. They come in a variety of lock functions depending on your application. The common lock backset for hollow metal doors is 2-3/4". The door prep for a cylindrical lock is known as "161 lock prep."

Strike Plate:
This is the plate mounted to the door frame. The cylindrical lock's latchbolt strikes this plate when it closes in order to depress it. When the hollow metal door is then in the full closed position, the hole in the strike plate, allows the lock's latchbolt to slide out inside of the strike plate, securing the door and locking it.

Ball Bearing Hinge:
This is the pivoting mechanism of the hollow metal door. Depending on your hollow metal door height, you will have 4 hinges for 8'-0" tall doors, or 3 hinges for 6'-8" and 7'-0" tall doors. If the door is an exterior door and the hinges are exposed to the outside of the building, the hinges must be the non-removable pin type (NRP), in order to safely secure the door. If removable pin hinges are used, the hinges and door can be removed from the outside.

Door Sweep:
This is the weatherstripping used at the bottom of the hollow metal door. It provides a sealed barrier from debris, wind, insects, and even small rodents.

Door Threshold:
This is the bottom extruded steel plate mounted to the ground in between the door frame. When the door is closed, the bottom sweep seals against the door threshold. This should be used on every exterior hollow metal door.

Hollow Metal Door Lock Types

A lock is a mechanism which secures the hollow metal door in the closed position with the door frame. There are a variety of custom locks which can be used. Below is a chart of the most popular lock types.

Cylindrical lock:
A cylindrical lock is a locking mechanism which requires two holes to be bored into the door known as the edge bore and the face bore. The face bore is the large hole drilled into the face of the door. This is where the lock will be installed through the door, with a lever or knob on each side of the door. The edge bore, is the smaller hole drilled into the edge of the door, where the cylindrical lock's latchbolt will install. The prep work of the face bore and edge bore is commonly referred to as "161" lock prep. There are many advantages to cylindrical locks in hollow metal doors. For one the installation time is very small for cylindrical locks compared to that of mortise locks. That also make cylindrical locks easy to replace if you ever needed to. Another advantage is that there are a variety of cylindrical lock types to choose from. For example, high end commercial grade cylindrical locks often feature a built in clutch mechanism inside of their lock chassis, which helps prevent the lever from breaking off in the event of a security breach or abuse. Another advantage of cylindrical locks is that they are relatively inexpensive compared to mortise locks or exit devices.

Mortise lock: A mortise lock is a locking mechanism which requires a pocket to be cut into the door. Mortise locks are very secure, however they typically require alot more time for installation. Most mortise locks vary in the face prep. Hollow metal doors are often prepped from the manufacturer with the mortise cutout, however they do not prep for the face cutout since so many mortise locks vary. This requires the installer to do special door preparation in order to install the mortise lock. Mortise locks are much more expensive than cylindrical locks, however are more secure. Also, if you need to replace your existing mortise lock later on, you pretty much have to use the exact same mortise lock model, otherwise you may need to modify the door. One advantage of mortise locks is that they provide more security than a cylindrical lock.

Cylindrical Lock and Deadbolt Combination: A deadbolt is a locking mechanism that requires two holes to be bored into the door; the same process as a cylindrical lock. Unlike a cylindrical lock the deadbolt lock is not spring loaded or beveled. The security bolt is also longer than the cylindrical lock latchbolt and is able to extend further into the door frame. A deadbolt lock is typically located above the cylindrical lock. A hollow metal door with both a cylindrical lock and deadbolt provides the best security for a lower price than the mortise lock.

Exit Device: An exit device is a push pad locking device mounted to the face of the secure side of the door (used on left hand reverse or right hand reverse doors). Exit devices are often used due to fire code requirements. Exit devices are available in three types: rim, surface vertical, and concealed. Rim exit devices are the most popular.

Common Hollow Metal Door Sizes

Hollow metal doors come in a variety of sizes. The most common door widths are shown in the chart below. These door widths include 2'-0" (24"), 2'-4" (28"), 2'-6" (30"), 2'-8" (32"), 2'-10" (34"), 3'-0" (36"), 3'-4" (40"), 3'-6" (42"), 3'-8" (44"), and 4'-0" (48"). The common hollow metal door heights are 6'-8" (80"), 7'-0" (84"), and 8'-0". All hollow metal door sizes (both width and height) are considered nominal heights and widths. The exact hollow metal door width is actually about 1/4" less than the nominal width. For example, a 3'-0" (36") wide hollow metal door's actual width is approximately 35-3/4". Likewise the actual door height is about 7/8" less than the nominal height. For example, a 6'-8" (80") height hollow metal door's actual height is approximately 67-1/8". Now you might be asking, why is that the actual size? Remember a hollow metal door is designed to fit within a steel door frame. The deduction of the height and width or undercut is what allows the hollow metal door to fit within the door frame.

Actual Hollow Metal Door Width = Nominal Door Width - 1/4"
Actual Hollow Metal Door Height = Nominal Door Height - 7/8"

Fire Rated Hollow Metal Doors

A fire rated hollow metal door is a commercial steel door designed to not combust or spread fire for a specific time period. Fire doors are available in five different types of ratings from 20 minutes (1/3 hour), 45 minutes (3/4 hour), 60 minutes (1 hour), 90 minutes (1-1/2 hour), and 180 minutes (3 hour). Depending on your state or jurisdiction, you may be required to have a fire rated door up to 3 hours. If a hollow metal door has been fire rated it will have a label as shown in the illustration below. The label will be located on the hinge or heel side of the hollow metal door and will indicate to building inspectors that the door has been approved to withstand fire for specified period of time listed on the fire label. So how does a door become fire rated? Fire ratings are determined by a testing agency in accordance with the requirements set forth by the International Building Code, International Fire Code, and the National Fire Protection Agency (NFPA 80). Depending on the location of the wall or building application will also play a factor in the required fire rating.

Fire Code Requirements

The architectural drawing or blueprint will list the required fire rated doors on the door schedule. The various fire rated door requirements are based on the type of fire rated wall the door is being installed on. Currently, steel is the only economical door material which can be fire rated up to 3 hours. There are other specialty door materials which have been fire rated, however they are extremely expensive and not an industry norm.
-A 3 Hour Rating is typically used on a 4 hour wall rating. This opening type is in a wall that separates buildings or divides a single building into designated fire areas.
-A 1-1/2 Hour Rating is typically used on a 2 hour wall rating. This opening type is used in enclosures of vertical communication or egress through buildings, such as stairwells and elevator shafts. This opening type is also used in a wall where there is the potential for severe fire exposure from the exterior of the building.
-A 1 Hour Rating is typically used on a 1 hour wall rating. This door and frame type divides occupancies in a building.
-A 3/4 Hour Rating is typically used on a 1 hour wall rating. This door and frame type is used where there are openings in corridors or room partitions.

Hollow metal doors must meet the requirements set by the International Building and International Fire Code as well as NFPA 80. Fire ratings can vary from 20 minutes to 3 hours depending on the wall of the building. Temperature rise doors help retard the transmission of heat through the door. These are typically used in stairwells so people can safely pass the floors with an active fire. Remember, if the wall is fire rated, then the door and frame must be fire rated too.

Replacing A Fire Rated Hollow Metal Door

If you are replacing an existing hollow metal door you can check to see if it is a fire rated door by swinging the door open. Located near the top hinge on the door will be the fire label.

Americans with Disabilities Act (ADA) Requirements

The American with Disabilities Act or A.D.A. are a set of standards and design requirements created to ensure access to buildings for people with disabilities. According to ADA requirements atleast 60% of public entrances must be accessible in new construction. Public entrances are described as all entrances except for restricted or service entrances. If entrances are restricted, atleast one must comply in addition to the public entrances required to be accessible. ADA compliance is required for doors providing passage on accessible routes. There must be atleast one accessible door serving each accessible room, space, and entrance. In order for a hollow metal door to be ADA compliant, the door system must meet the following requirements below.

Closing Speed: Hollow metal door should have a door closer installed. The door closer should take atleast 5 seconds minimum to close the door from the 90 degree full open door position to 12 degrees. If spring hinges are used on the door instead of a door closer, the door should take atleast 1.5 seconds to close from the 70 degree open position to 0 degrees closed.

Opening Force: Hollow metal door should have a 5lb max opening force to open the door. This excludes exterior hinged and fire doors.

Vision Glass Lite: If a vision lite is installed on a hollow metal door the accessible viewing height should be 43" max, unless it is not intended for viewing.

Hardware: All door hardware must comply with ADA standards.

Smooth Surface (Kick Plate): Hollow metal door should have a kickplate on the push side of the door, which is atleast 10" high.

Threshold: Hollow metal door should have a threshold that is no higher than 1/2" and is beveled if above 1/4".

Maneuvering Clearance: Required maneuvering clearance for the hollow metal door provides space for opening and proceeding through the hollow metal door using a wheelchair or other mobility aid. The required door clearance provides unobstructed space for maneuvering through doorways. Maneuvering clearances must be free of any protrusions the full height of atleast 80" minimum and changes in the floor (other than thresholds).

Clear Width: The clear width is measured from the stop to the face of the hollow metal door open 90 degrees. No projection into the clear width is permitted below 34". In other words, the hollow metal door size must be atleast 3'-0" (36").

Vertical Clearance: The required vertical clearance of the hollow metal door is atleast 80" or 78" from the door closer to the floor. In other words, the hollow metal door size should be atleast 6'-8" (80").

Hollow Metal Door Common Lock and Hinge Preps

A commercial hollow metal door is a 1-3/4" thick door comprised of two steel sheets and an inner core of some type. Hollow metal doors that are 6'-8" (80") or 7'-0" (84") are prepped for 3 each 4.5" x 4.5" ball bearing door hinges. Hollow metal doors that are 8'-0" (96") tall are prepped for 4 each 4.5" x 4.5" ball bearing hinges. Each hinge prep location is reinforced with a thicker gauge hinge reinforcement plate, to ensure that the hinge points will be strong. There are four common lock preps available for hollow metal doors: blank lock prep, 161 cylindrical lock prep, 86 mortise edge prep, and RPD rim panic exit device prep.

Blank Prep: A blank prep hollow metal door has no lock preparation. Hollow metal doors can be ordered this way if there is no lock needed. For example a hollow metal door with a push and pull plate would not require a lock prep, so the blank prep would be suitable.

A 161 cylindrical lock prep is by far the most popular hollow metal door lock prep type. The prep is for a standard 2-3/4" backset commercial cylindrical lock. Also available is a deadbolt prep, which the same prep but located above the cylindrical lock bore hole.

An 86 mortise prep is designed for hollow metal doors that will use a mortise lock.

An RPD rim panic prep is for hollow metal doors that will use an exit device. Although on the exterior an RPD prep looks like a blank prep, it actually has reinforcement internally to help support the mounting of an exit device.

Hollow Metal Door Handing Configurations

Commercial hollow metal doors can be ordered in a variety of ways from single door packages, to door pairs, or even slabs. The handing varies depending on the hollow metal door configuration.

A single hollow metal door package typically includes a hollow metal door with a steel door frame, a cylindrical lock, and door hinges. Single hollow metal door packages are offered in 4 different handing types: right hand reverse (RHR), Left Hand Reverse (LHR), Right Hand (RH), or Left Hand (LH).

A hollow metal door paired package, or hollow metal double door package, typically includes two door panels (an active door panel and inactive door panel), a steel door frame, a cylindrical lock, and door hinges. Hollow metal door paired packages are offered in 4 different handings: Right Hand Reverse Active (RHRA), Left Hand Reverse Active (LHRA), Right Hand Active (RHA), and Left Hand Active (LHA).