This guide reflects CDF Distributors' standard specifications and field-tested recommendations used by commercial contractors nationwide. The information is provided for specification and selection purposes. Always verify requirements with the Authority Having Jurisdiction (AHJ) for your project location.

For questions or to order a complete door assembly, contact CDF at (855) 769-9895 or sales@cdfdoors.com. Configure your assembly online at ProBuilder: cdfdistributors.com.

About This Guide

What is UL 1784 and when is it required?

UL 1784 is the test standard for air leakage through door assemblies, used to evaluate smoke gasket performance. It is required by the IBC on fire-rated corridor doors, smoke barrier doors, and smoke partition doors in many occupancy types.

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

Smoke gaskets seal against air and smoke leakage at ambient and moderate temperatures. Intumescent seals contain a reactive material that expands at high temperatures (250-400 degrees F) to fill the door-to-frame gap during a fire. Many fire-rated assemblies require both.

What fire ratings require intumescent seals?

Intumescent seals are commonly required at 45, 60, 90, and 180-minute fire ratings. At the 20-minute level, smoke gaskets are typically required but intumescent seals may not be, depending on the assembly listing. All five commercial fire-rating levels (20, 45, 60, 90, and 180 minutes) should be verified against the specific assembly listing.

What is an automatic door bottom?

An automatic door bottom is a mortise-mounted device that drops a neoprene or silicone seal to the floor when the door closes and retracts the seal when the door opens. It provides the tightest bottom seal and is standard in acoustic and fire-rated assemblies.

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

No. Fire-rated assemblies are tested and listed with specific gasket models and configurations. Substituting an unlisted gasket invalidates the fire rating. Always verify the seal model against the specific UL, WHI, or Intertek assembly listing.

What seal brands does CDF supply?

CDF supplies Pemko and National Guard Products (NGP) seals and gaskets through the FlashShip inventory program. Both brands offer complete lines of smoke gaskets, intumescent seals, acoustic seals, automatic door bottoms, sweeps, and perimeter gasketing.

Does ProBuilder select the correct seals for fire-rated assemblies?

Yes. When a fire-rated assembly is configured in ProBuilder, the tool identifies required seal components based on the assembly listing, ensuring the specified gaskets and intumescent seals match the tested configuration.

Frequently Asked Questions

CDF's ProBuilder tool allows contractors and facility managers to configure complete door, frame, and hardware assemblies online. During configuration, you can select the specific components discussed in this guide and receive an instant quote.

For assistance or to order a complete door assembly, call (855) 769-9895 or email sales@cdfdoors.com. CDF's sales team is available to help you specify the right components for your project.

Configure Your Door Assembly

CDF Distributors supplies door seals and gaskets from several different Brands including Zero, Pemko, Hager and National Guard Products (NGP). These Brands offer comprehensive product lines covering smoke gaskets, intumescent seals, acoustic seals, automatic door bottoms, surface-mounted sweeps, and perimeter gasketing for all commercial applications.

CDF's ProBuilder configuration tool coordinates seal selection with the door, frame, and hardware assembly. When a fire-rated assembly is configured in ProBuilder, the tool identifies the required seal components based on the assembly listing, ensuring that the specified gaskets and intumescent seals match the tested configuration.

Specifying Door Seals and Gaskets Through CDF Distributors

Fire-rated door assemblies require seals that are tested and listed as part of the complete assembly. The five standard commercial fire-rating levels — 20, 45, 60, 90, and 180 minutes — each impose specific requirements on the seal package.

At the 20-minute rating level, smoke gaskets are typically required but intumescent seals may not be. At 45 and 60-minute ratings, both smoke gaskets and intumescent seals are commonly required, depending on the assembly configuration and the testing laboratory's listing. At 90 and 180-minute ratings, intumescent seals are standard requirements, and the seal placement, material composition, and installation method are tightly specified in the listing.

When specifying seals for fire-rated assemblies, always reference the specific assembly listing (UL, WHI, or Intertek) to confirm which seal models and configurations are approved. Substituting an unlisted seal model — even if it appears physically identical — invalidates the fire rating and creates a code violation.

Seal Compatibility with Fire-Rated Door Assemblies

The gap at the bottom of the door is the most challenging seal point because the seal must accommodate the door's swing arc and avoid interference with flooring materials. Three primary approaches address this gap: automatic door bottoms, surface-mounted door sweeps, and threshold-and-seal combinations.

Automatic door bottoms are mortised into the bottom edge of the door and use a plunger mechanism activated by the door frame's strike jamb. When the door closes, the plunger depresses and a neoprene or silicone seal drops to the floor or threshold surface. When the door opens, the seal retracts to clear the floor. Automatic door bottoms provide the tightest seal and are standard in acoustic and fire-rated assemblies.

Surface-mounted door sweeps are attached to the push or pull face of the door and use a flexible blade or brush to sweep against the floor or threshold. Sweeps are less effective than automatic door bottoms but are easier to install and replace, making them suitable for environmental sealing where acoustic or fire-rated performance is not required.

Thresholds work in conjunction with door bottoms to create a complete seal at the floor line. ADA-compliant thresholds must not exceed 1/2 inch in height for hinged doors, and the threshold surface must be beveled with a slope no greater than 1:2.

Door Bottoms and Thresholds

Perimeter gaskets are installed on the frame head and both jambs to seal the gap between the door panel and the frame when the door is closed. These gaskets serve smoke, acoustic, light, and environmental sealing functions depending on the material and profile.

Common perimeter gasket profiles include compression seals (bulb or blade profiles that compress against the door face), magnetic seals (used primarily in acoustic applications for a positive seal), and brush/fin seals (used for light and air infiltration control where compression seals are not practical).

For fire-rated applications, perimeter gaskets must be part of the tested and listed assembly. Self-adhesive gaskets applied in the field may not satisfy the listing requirements unless they are specifically included in the assembly's tested configuration. Specifiers should verify that the gasket model and installation method are covered by the assembly listing.

Perimeter Gaskets: Head and Jamb Seals

Intumescent seals contain a chemically reactive material that expands when exposed to heat, filling the gaps between the door and frame during a fire to prevent the passage of flames and hot gases. Unlike smoke gaskets, which function at ambient and moderate temperatures, intumescent seals activate at temperatures typically between 250 and 400 degrees F and expand to several times their original volume.

In fire-rated door assemblies, intumescent seals are installed in a kerf (groove) milled into the door edge, the frame rabbet, or both. The seal remains flush or slightly recessed during normal operation and does not affect the door's swing or latching. During a fire, the intumescent material expands to fill the clearance gap, maintaining the integrity of the fire barrier.

Fire-rated door assemblies are tested to NFPA 252 (Standard Methods of Fire Tests of Door Assemblies) or UL 10C (Positive Pressure Fire Tests of Door Assemblies). The intumescent seal is tested as part of the complete assembly, and its performance is integral to achieving the assembly's fire rating. Commercial fire-rated door assemblies are available in 20, 45, 60, 90, and 180-minute ratings, and the intumescent seal specification must match the assembly's target rating.

It is important to distinguish between intumescent seals and smoke gaskets. In many fire-rated assemblies, both are required: the smoke gasket controls air leakage at ambient and moderate temperatures, while the intumescent seal activates at higher temperatures to maintain the fire barrier. The two components serve different functions and are not interchangeable.

Intumescent Seals for Fire-Rated Assemblies

Smoke gaskets prevent the passage of smoke and toxic gases through the gaps around a closed door during a fire event. The governing test standard is UL 1784 (Air Leakage Tests of Door Assemblies), which measures the volume of air that passes through a closed door assembly at ambient and elevated temperatures.

UL 1784 testing is conducted at both ambient temperature (75 degrees F) and elevated temperature (400 degrees F). A door assembly passes the test if the air leakage rate does not exceed 3.0 cubic feet per minute per square foot of door opening at the ambient temperature condition. Many jurisdictions and fire codes reference UL 1784 as a mandatory requirement for fire-rated corridor doors, stairwell doors, and smoke barrier doors.

Smoke gaskets are installed on the frame head and jambs (perimeter gaskets) and at the meeting stiles of pairs of doors. The gasket material is typically a flexible silicone, neoprene, or TPE (thermoplastic elastomer) strip that compresses against the door face when the door is closed, creating an air-tight seal.

The International Building Code (IBC) requires smoke gaskets on fire-rated corridor doors in specific occupancy types and on doors in smoke barriers and smoke partitions. When smoke gaskets are required, they must be tested and listed as part of the complete door assembly, not added as field-applied aftermarket components.

Smoke Gaskets and UL 1784 Compliance

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 application requirements is essential for correctly specifying commercial door assemblies across fire-rated, and environmental applications.

The Role of Door Seals and Gaskets in Commercial Openings

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?