What is the difference between a cylindrical lock prep and a mortise lock prep?

A cylindrical lock prep consists of a 2-1/8 inch cross bore through the door face and a 1 inch edge bore at a 2-3/4 inch backset. A mortise lock prep is a rectangular pocket machined into the door edge to accept the entire mortise lock body. The two preps are not interchangeable.

Can I change the door prep after the door has been manufactured?

Field modifications to change a door prep are not recommended, especially on fire-rated doors where unauthorized modifications void the fire label. The preferred approach is to order the correct prep from the factory.

What minimum trim size is required to cover a cylindrical lock prep?

The lock rose or exit device trim plate must be at least 3-1/4 inches in diameter to fully cover the enhanced cylindrical lock prep with through-bolt notching.

Do fire-rated doors require different preparations than non-rated doors?

Fire-rated doors (20-minute, 45-minute, 60-minute, 90-minute, and 3-hour) use the same general prep types but all preparations must be applied at the factory in accordance with the door's fire listing. Field modifications are prohibited.

How does door handing affect the door prep?

Door handing determines which edge receives the hinge prep and which edge receives the lock prep. All preparations are machined based on the specified hand. A door prepped for one hand cannot be flipped to serve as the opposite hand.

What is closer reinforcement and when is it needed?

Closer reinforcement is an internal steel plate welded inside the top rail of a hollow metal door. It provides structural support for surface-mounted door closer screws and is needed any time a surface-applied closer is specified.

Can a door be prepped for both an exit device and a deadbolt?

Yes, a door can receive multiple preparations for different hardware. Each prep must be specified separately at the time of order.

What happens if the exit device trim does not cover the door prep?

If the exit device trim does not fully cover the door prep cutout, the machined openings will be visible. The door should be ordered with a blank face at the lock location and prepped specifically for the exit device.

What is UL 1784 and when is it required?

UL 1784 tests air leakage through door assemblies for smoke gasket performance. It is required by the IBC on fire-rated corridor doors, smoke barrier doors, and smoke partition doors.

What is the difference between a smoke gasket and an intumescent seal?

Smoke gaskets seal against air and smoke at ambient temperatures. Intumescent seals expand at high temperatures to fill the door-to-frame gap during a fire. Many assemblies require both.

What fire ratings require intumescent seals?

Intumescent seals are commonly required at 45, 60, 90, and 180-minute ratings. All five levels (20, 45, 60, 90, 180 minutes) should be verified against the assembly listing.

Can I substitute a different gasket on a fire-rated door?

No. Fire-rated assemblies are tested with specific gaskets. Substituting unlisted gaskets invalidates the fire rating.

What seal brands does CDF supply?

CDF supplies Pemko and National Guard Products (NGP) seals and gaskets through the FlashShip inventory program.

What is the maximum threshold height allowed under ADA for new construction?

The maximum threshold height for new construction on accessible routes is 1/2 inch (13 mm). Any threshold higher than 1/4 inch must have beveled edges with a maximum slope of 1:2.

Does CDF supply Pemko thresholds?

Yes. CDF Distributors supplies Pemko commercial thresholds through its FlashShip distribution program. Thresholds can be specified as part of a complete door assembly in CDF's ProBuilder configuration tool.

What is the difference between the active leaf and the inactive leaf on a double door?

The active leaf is the primary operating door used for daily traffic. It carries the lockset or primary exit device and swings freely. The inactive leaf remains closed most of the time and is secured by flush bolts or a surface vertical rod exit device.

When do I need a door coordinator on a pair of doors?

A coordinator is required whenever a pair has an overlapping astragal. The coordinator ensures the inactive leaf closes first so the astragal overlaps correctly. On fire-rated pairs, a coordinator is mandatory per NFPA 80.

Can I use two rim exit devices on a double door opening?

No. Two rim exit devices create a latching conflict at the meeting stile. The correct configuration is a rim exit device on the active leaf and a surface vertical rod (SVR) exit device on the inactive leaf.

What type of flush bolts are required on fire-rated double doors?

Fire-rated pairs require automatic (self-latching) flush bolts on the inactive leaf. Manual flush bolts are generally not permitted because there is no guarantee they will be engaged during a fire event.

What is the difference between an astragal and a mullion?

An astragal is attached to one door leaf and overlaps the gap between meeting stiles. It moves with the door. A mullion is a fixed vertical member anchored to the frame head and floor, dividing the opening into two separate single-door openings.

What are the fire rating levels available for double door assemblies?

Double door assemblies are available at five fire rating levels: 20-minute, 45-minute, 60-minute, 90-minute, and 3-hour (180-minute). All components must be listed and labeled at or above the required rating.

How do I determine the handing of a double door opening?

Stand on the outside of the opening (key side or pull side). The hand is determined by the active leaf. If the active leaf hinges are on the right, it is a right-hand pair. If on the left, it is a left-hand pair.

What happens if the astragal is missing on a fire-rated pair?

A fire-rated pair without an astragal will fail fire inspection. The gap between meeting stiles allows smoke and flame passage, compromising the fire barrier. NFPA 80 requires a listed overlapping astragal on fire-rated pairs.

What is the difference between a rim exit device and a vertical rod exit device?

A rim exit device latches into a strike on the door frame jamb using a single latchbolt. A vertical rod exit device uses rods that extend to the top and bottom of the door, latching into strikes in the header and floor. Rim devices are used on single doors and pairs with one active leaf. Vertical rod devices are used on pairs where both leaves must open independently.

When do I need a surface vertical rod exit device instead of a rim device?

A surface vertical rod device is required when both leaves of a double-door pair must be active. Vertical rod devices latch into the header and floor, eliminating the need for a center mullion between the two doors.

What is the difference between a crossbar and a touchbar exit device?

A crossbar is a full-width bar that projects from the door face and pivots when pushed. A touchbar is a flat, low-profile pad that depresses when touched or pushed. Both meet code requirements for panic and fire exit hardware.

Do fire-rated doors require fire-rated exit devices?

Yes. An exit device on a fire-rated door assembly must be listed as fire exit hardware with a rating matching or exceeding the assembly rating. Standard levels are 20-minute, 45-minute, 60-minute, 90-minute, and 3-hour (180-minute).

What exterior trim options are available for exit devices?

Standard exterior trim options include lever trim, knob trim, thumbpiece trim, pull handles, and no trim (exit only). Lever trim is required on accessible routes per ADA and most building codes.

Can I use a rim exit device on a double door?

Yes, but only when one leaf is active and the other is inactive. The rim device goes on the active leaf with flush bolts on the inactive leaf. If both leaves must be active, vertical rod devices are required.

What building codes require exit devices on commercial doors?

The IBC and NFPA 101 require panic hardware on doors serving assembly occupancies with loads of 50 or more, and educational occupancies with loads of 100 or more. Fire exit hardware is required on fire-rated openings that also require panic hardware.

What is exit device trim?

Exit device trim is the hardware mounted on the exterior (pull) side of a door equipped with an exit device. The trim determines whether and how the door can be entered from outside. Options include dummy trim, pull trim, lever trim, and night latch trim.

Can I use exit trim from one manufacturer with an exit device from another?

No. Exit trims are brand-specific and are not interchangeable between manufacturers. The tailpiece geometry, mounting hole pattern, and internal mechanism differ between brands.

What is the difference between entry function and storeroom function lever trim?

Entry function lever trim can be unlocked with a key and remains unlocked until manually re-locked. Storeroom function requires the key to be actively held and turned to retract the latch. When the key is released, the storeroom lever immediately returns to the locked position.

Are exit device trims field-reversible?

No. Exit device trims are handed and cannot be reversed in the field. A left-hand trim will not work on a right-hand door. The correct handing must be determined before ordering.

Do I need exit trim on a fire-rated door?

Exit trim is only required if the door needs to allow entry from the exterior side. If entry is required, the trim must be listed and labeled for the fire rating. Fire-rated assemblies are available at 20-minute, 45-minute, 60-minute, 90-minute, and 3-hour (180-minute) levels.

What door prep is required for lever trim?

The required door prep depends on the specific trim model and exit device series. The door must be factory-prepped with the correct cutouts and reinforcements. When ordering from CDF, the correct door prep is automatically applied based on the selected configuration.

What trim type should I use for a main entrance with an exit device?

For a main entrance requiring keyed entry from outside, lever trim with the entry function is the standard choice. For buildings with electronic access control, an electrified lever trim or pull trim paired with electronic latch retraction may be more appropriate.

What is night latch trim and when is it used?

Night latch trim adds a deadlocking function to the exterior side of the door. When engaged, it prevents the exit device latch from being shimmed or manipulated from outside. It is used on high-security exterior doors and after-hours entry points.

What is a filler plate on a commercial door?

A filler plate is a flat steel plate that covers an unused hardware cutout on a commercial door or frame. When hardware is changed, upgraded, or removed, the original prep may be left exposed. A filler plate screws into place over that opening, restoring the door's finished surface and structural integrity.

When do I need a filler plate?

A filler plate is needed any time a hardware change leaves an unused cutout on a commercial door or frame. Common scenarios include converting from a mortise lock to a cylindrical lock, upgrading to a different lock model, repurposing a prepped door, or removing hardware without installing a replacement.

What is the difference between a mortise filler plate and a cylindrical filler plate?

A mortise filler plate covers the rectangular pocket cut into the door edge for a mortise lock body. A cylindrical filler plate covers the circular bore holes cut through the door face and edge for a cylindrical lever lock or knob lock.

Are filler plates required on fire-rated doors?

Yes. On fire-rated door assemblies, every opening must be covered with a listed, fire-rated component. Filler plates used on fire-rated doors must be listed for the specific rating level: 20-minute, 45-minute, 60-minute, 90-minute, or 3-hour (180-minute).

How do I identify which filler plate I need?

Look at the exposed cutout on the door edge. A rectangular pocket indicates a mortise prep; a circular bore indicates a cylindrical prep. Note the door thickness, door material, and desired finish. CDF's sales team can identify the correct filler plate from a photo of the exposed prep.

Can I reuse a filler plate from another door?

A filler plate can be reused if it matches the prep type, door thickness, and finish of the new door. On fire-rated assemblies, the filler plate must be listed for the specific fire rating of the assembly.

Do filler plates affect door security?

An uncovered hardware prep weakens the door edge and creates a potential security vulnerability. A properly installed filler plate restores the structural continuity of the door edge.

How are filler plates installed?

Filler plates attach with machine screws through pre-drilled holes in the plate. The plate is positioned over the exposed cutout, aligned with screw holes, and secured. The installed plate sits flush with the surrounding door surface.

What does it mean for a fire-rated assembly to be listed?

A listed fire-rated assembly has been tested to ASTM E119 or UL 10C standards and is documented in the UL Fire Resistance Directory or WHI Certified Listings Directory. The listing specifies exactly which door, frame, and hardware components may be used together. Only assemblies built from listed components maintain their fire rating.

Can I substitute hardware that looks identical but comes from a different manufacturer?

No. Fire-rated assembly listings are manufacturer-specific. Even if two products appear identical, only the manufacturer listed in the UL or WHI directory is approved for that assembly. Substituting unlisted components voids the assembly's fire label.

Who is responsible if non-listed components are found during inspection?

Both the specifier and the installer share responsibility. The specifier must ensure the hardware schedule references listed components, and the installer must verify that delivered components match the specification. The Authority Having Jurisdiction (AHJ) can require removal and replacement of non-compliant assemblies.

What fire ratings are available for commercial door assemblies?

Commercial fire-rated door assemblies are available in 20-minute, 45-minute, 60-minute, 90-minute, and 180-minute ratings. The required rating depends on the wall construction and the building code requirements for that specific opening.

Page 2 - Commercial Door Parts & Hardware Guide

Parts and Hardware

What Are Commercial Door Preparations and How Do They Affect Hardware Selection?

Jason Searcy - March 29, 2026 - 18 min read

A door preparation (commonly called a "door prep") is a factory-machined cutout in a commercial steel or wood door that allows specific hardware to be installed. Every commercial door—except unprepped wood slab doors—ships with one or more preparations that determine which locks, exit devices, hinges, closers, and other hardware can be mounted to it. Selecting the correct door prep at the time of order eliminates field modifications, reduces installation time, and ensures the hardware fits and functions as designed.

CDF Distributors fabricates commercial door assemblies with factory-applied preparations at its Nashville, Tennessee facility. You can configure doors with the correct preparations using CDF’s ProBuilder tool at cdfdistributors.com. For assistance selecting the right prep for your hardware, call (855) 769-9895 or email sales@cdfdoors.com.

What Is a Door Preparation?

A door preparation is a set of holes, cutouts, reinforcements, and mortises machined into a door at the factory

Parts and Hardware

What Types of Door Seals and Gaskets Are Required for Fire-Rated Openings?

Jason Searcy - March 29, 2026 - 9 min read

A specification guide to smoke gaskets, intumescent seals, acoustic seals, and perimeter gasketing for commercial door assemblies.

This guide answers: What Types of Door Seals and Gaskets Are Required for Fire-Rated Commercial Openings?

The Role of Door Seals and Gaskets in Commercial Openings

Door seals and gaskets are critical components of commercial door assemblies that control the passage of smoke, fire, sound, light, air, and water through the gaps between the door panel and the frame. While often treated as secondary hardware, seals and gaskets directly affect a building's fire-safety performance, acoustic isolation, energy efficiency, and compliance with accessibility standards.

In fire-rated assemblies, seals and gaskets are not optional accessories — they are required components of the tested and listed assembly. Removing or substituting gaskets outside the listed configuration invalidates the fire rating.

Understanding the types of seals, their governing standards, and their

Parts and Hardware

How Do You Select a Commercial Door Threshold That Meets ADA Height Requirements?

Jason Searcy - March 29, 2026 - 7 min read

A specification guide to commercial door threshold types, ADA compliance, material selection, and application criteria for interior and exterior openings.

This guide answers: How do you select a commercial door threshold that meets ADA height requirements?

Role of Thresholds in Commercial Door Assemblies

A threshold is the horizontal component installed at the bottom of a door frame, spanning the width of the opening at floor level. Thresholds serve multiple functions: they provide a transition between flooring surfaces, seal the gap between the door bottom and the floor to control air infiltration, water penetration, and light transfer, and they contribute to the structural integrity of the door frame at the floor line.

In commercial construction, threshold selection is governed by accessibility requirements (ADA/ABA), energy codes, fire ratings, and environmental exposure. The wrong threshold can create an ADA violation, compromise a fire-rated opening, or allow water intrusion at an

Parts and Hardware

What Goes Wrong When Double Doors Are Misconfigured? A Complete Pair Configuration Guide

Jason Searcy - March 29, 2026 - 20 min read

Misconfigured double door openings are one of the most common sources of rework in commercial door installations. When a pair of doors is specified incorrectly, the consequences range from doors that will not close in the correct sequence to fire-rated assemblies that fail inspection. The most frequent errors involve incorrect active leaf designation, missing or wrong coordinators, incompatible astragal and mullion selections, and fire-rated pairs shipped without the hardware coordination required by code. This guide explains how each component of a double door opening works, what happens when it is configured incorrectly, and how to specify pairs correctly the first time.

CDF Distributors ships pre-configured double door assemblies from its Nashville, Tennessee headquarters. You can configure pair openings online using CDF’s ProBuilder tool at cdfdistributors.com, which validates hardware compatibility and coordinator requirements automatically. For assistance configuring a double door

Parts and Hardware

How to Choose the Right Exit Device for a Commercial Door

Jason Searcy - March 29, 2026 - 15 min read

The right exit device depends on three factors: door configuration (single or double), fire rating requirements, and whether the application calls for rim-mounted or vertical rod hardware. Rim exit devices are the standard choice for single doors and pairs with one active leaf. Surface vertical rod devices are required for double doors where both leaves are active. Concealed vertical rod devices provide the same function with hardware hidden inside the door. All three types are available in crossbar and touchbar styles, and all three can be specified with fire ratings from 20 minutes up to 3 hours depending on the assembly requirements.

CDF Distributors supplies exit devices as part of complete door and frame assemblies configured through its ProBuilder tool at cdfdistributors.com. Exit devices are surface-mounted hardware, meaning they install on the face of the door after the door and frame are set. CDF does not prep doors or frames for surface-mounted hardware such as exit devices; the

Parts and Hardware

What Are the Different Types of Exit Device Trim and How Do You Choose the Right One?

Jason Searcy - March 29, 2026 - 13 min read

Exit device trim is the hardware mounted on the exterior (pull) side of a door equipped with an exit device. The trim type determines how people enter the building from outside while the exit device controls egress from the interior. The four standard trim types are dummy trim, pull trim, lever trim, and night latch trim. Each serves a different access control function: dummy trim provides no exterior entry, pull trim allows pulling without retracting the latch, lever trim enables keyed or free entry by retracting the latch from outside, and night latch trim adds a deadlocking feature for higher-security applications. Choosing the correct trim depends on the required entry function, the door’s fire rating, and the exit device brand already specified for the opening.

CDF Distributors ships complete exit device and trim assemblies from its Nashville, Tennessee headquarters. You can configure and order exit devices with matching trim online using CDF’s ProBuilder tool at cdfdistributors.com.

Parts and Hardware

What Are Filler Plates for Commercial Doors and When Do You Need Them?

Jason Searcy - March 29, 2026 - 12 min read

Filler plates are flat steel cover plates that attach to a commercial door or frame to conceal unused hardware cutouts. When a door’s lock or latch hardware changes—whether during a retrofit, a hardware upgrade, or a lock conversion—the original cutout in the door edge or frame often remains exposed. A filler plate covers that opening, restoring the door’s structural integrity and finished appearance. Filler plates are required any time a hardware change leaves an open prep in a commercial hollow metal or wood door.

CDF Distributors stocks filler plates for standard mortise and cylindrical lock preps and can include them with any door or frame assembly configured through CDF’s ProBuilder tool at cdfdistributors.com. For help identifying the correct filler plate for your project, call (855) 769-9895 or email sales@cdfdoors.com.

What Is a Filler Plate?

A filler plate is a steel plate designed to cover an unused hardware preparation in a commercial door or frame. When commercial doors are

Parts and Hardware

What Happens When Fire-Rated Door, Frame, and Hardware Components Are Mismatched?

Jason Searcy - March 29, 2026 - 6 min read

Understanding UL and WHI listing requirements for fire-rated door assembly components

This guide answers: How Fire-Rated Door and Hardware Combinations Affect Assembly Listing Compliance

How Fire-Rated Listings Work

Every fire-rated door assembly must comply with a specific listing in the UL Fire Resistance Directory or the WHI Certified Listings Directory. These listings define the exact combination of door, frame, hardware, and glazing that may be used together to achieve a stated fire-resistance rating. The listing is not a general approval — it is a specific recipe that must be followed exactly.

Fire-rated assemblies are available in 20-minute, 45-minute, 60-minute, 90-minute, and 180-minute configurations. Each rating level has different requirements for component specifications, clearances, and labeling. Higher ratings generally require heavier gauge materials and more restrictive hardware selections.

Component Compatibility Rules

A fire-rated assembly is only valid when every component

Parts and Hardware

What Does a Fire-Rated Hospital Door Assembly Include?

Jason Searcy - March 29, 2026 - 11 min read

A fire-rated hospital door assembly is a complete, code-compliant door system designed for healthcare facility corridors, patient rooms, stairwells, and smoke compartment separations. The assembly can consist of a fire-rated hollow metal door or mineral core wood door in a hollow metal frame, paired with a wide selection of hardware including panic-rated exit hardware, an ADA-compliant door closer, heavy-weight ball-bearing hinges, and remote access solutions depending on the application. Every component must carry a matching fire rating and be listed together as a tested assembly. CDF Distributors configures and ships these assemblies as complete packages from its Nashville, Tennessee facility.

You can configure a hospital door assembly online using CDF’s ProBuilder tool at cdfdistributors.com. ProBuilder walks through each component selection and confirms compatibility across the full assembly. For assistance configuring a healthcare door package, call (855) 769-9895 or email sales@cdfdoors.com

Parts and Hardware

Fire-Rated Door Assemblies FAQ: Ratings, Requirements, and Compliance

Jason Searcy - March 29, 2026 - 16 min read

Fire-rated door assemblies are tested, labeled openings designed to resist the spread of fire and smoke for a specified duration. Every fire-rated opening consists of a door, frame, and hardware that have been tested together as an assembly and carry labels from a nationally recognized testing laboratory such as UL, Intertek (WHI), or FM. Fire ratings range from 20 minutes to 3 hours depending on the wall rating and the location of the opening within the building. Understanding what fire ratings mean, which components are required, and what field modifications are permitted is essential for specifying, installing, and maintaining compliant fire door assemblies.

CDF Distributors supplies complete fire-rated door and frame assemblies from its Nashville, Tennessee headquarters. You can configure and order fire-rated assemblies online using CDF’s ProBuilder tool at cdfdistributors.com. For assistance specifying a fire-rated assembly for your project, call (855) 769-9895 or email sales@cdfdoors.com

Page 2 - Parts and Hardware

What Are Commercial Door Preparations and How Do They Affect Hardware Selection?

What Is a Door Preparation?

What Types of Door Seals and Gaskets Are Required for Fire-Rated Openings?

The Role of Door Seals and Gaskets in Commercial Openings

How Do You Select a Commercial Door Threshold That Meets ADA Height Requirements?

Role of Thresholds in Commercial Door Assemblies

What Goes Wrong When Double Doors Are Misconfigured? A Complete Pair Configuration Guide

How to Choose the Right Exit Device for a Commercial Door

What Are the Different Types of Exit Device Trim and How Do You Choose the Right One?

What Are Filler Plates for Commercial Doors and When Do You Need Them?

What Is a Filler Plate?

What Happens When Fire-Rated Door, Frame, and Hardware Components Are Mismatched?

How Fire-Rated Listings Work

Component Compatibility Rules

What Does a Fire-Rated Hospital Door Assembly Include?

Fire-Rated Door Assemblies FAQ: Ratings, Requirements, and Compliance

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