IMPORTANT DISCLAIMER: This guide references the International Building Code (IBC), Chapter 7 (Fire and Smoke Protection Features), specifically Section 714 (Penetrations) and Section 715 (Joints and Voids), plus Section 710 (Smoke Barriers), Section 717 (Ducts and Air Transfer Openings), and Chapter 17 (Special Inspections); ASTM E814, Standard Test Method for Fire Tests of Penetration Firestop Systems; ASTM E1966, Standard Test Method for Fire-Resistive Joint Systems; ASTM E2307, Standard Test Method for Determining Fire Resistance of Perimeter Fire Barriers; ASTM E2174, Standard Practice for On-Site Inspection of Installed Firestop Systems; ASTM E2393, Standard Practice for On-Site Inspection of Installed Fire Resistive Joint Systems and Perimeter Fire Barriers; UL 1479; UL 2079; NFPA 101, Life Safety Code; and the International Fire Code (IFC), Chapter 7. These codes and standards vary by edition and are frequently amended by state and local jurisdictions. Section numbers shift between IBC editions. Local amendments and the edition adopted by your Authority Having Jurisdiction (AHJ) always control. This guide is a starting point only. Always verify the specific requirements applicable to your project with your local AHJ.

Firestopping is where rated assemblies most often fail. A listed firestop product does not create a compliant installation. The complete field condition must match the applicable system listing. The gap between the tested assembly and the installed assembly is where ratings are lost, and firestopping is the most common point of failure in that gap.

This article covers the testing standards that govern firestop systems, the components of a listed system, the code provisions that decide when each rating is required, the inspection standards that verify compliance, and the documentation and maintenance practices that keep a firestop program working for the life of the building.

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◆ Section 1: Why Firestop Systems Fail

Firestop failures occur for predictable reasons, and understanding them is the first step toward preventing them.

Key point: The rating belongs to the complete system: every component, every dimension, every material. If the field condition does not match the listing, it is not a tested system.

Key Article: Article 131 — Fire-Resistance-Rated Assemblies and UL Listings

Pro Tip: The most common field failure is not a missing product. It is a product installed in a configuration that was never tested.

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◆ Section 2: Regulatory Framework

Firestop systems are governed by a coordinated set of code provisions, test standards, and inspection practices.

Key point: The IBC establishes when firestopping is required. The ASTM and UL standards establish how systems are tested and how installations are inspected. The IFC keeps them intact after occupancy.

Key Article: Article 64 — Firestopping and Penetration Sealing — Essential Details

Pro Tip: ASTM E2174 and E2393 are referenced in IBC Chapter 17 as the standards for special inspection of firestop and joint systems.

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◆ Section 3: Testing Standards — What Each One Covers

A. ASTM E814 / UL 1479 — Through-Penetration Firestop Systems

ASTM E814 is the test method for firestop systems used in openings in fire-resistive walls and floors. The test evaluates:

• F-rating: the time flames do not pass through the system
• T-rating: the time for the unexposed side to reach 325°F above ambient (the test also tracks temperature at the penetrating item)

The test also includes a hose stream test, which checks that the system stays in place when it is struck by water after fire exposure. The F-rating is based on flame occurrence on the unexposed surface, while the T-rating is based on temperature rise.

UL 1479 adds optional ratings that matter for smoke-rated construction:

• L-rating: air leakage through the system at ambient and elevated temperatures, relevant to smoke barriers and smoke partitions
• W-rating: resistance to water passage, relevant where water tightness is specified

Important limitation: ASTM E814 does not cover membrane penetrations of floor-ceiling or roof-ceiling assemblies, which are evaluated as part of the ASTM E119 assembly test, nor membrane penetrations of load-bearing walls.

B. ASTM E1966 / UL 2079 — Fire-Resistive Joint Systems

ASTM E1966 evaluates joint systems designed for use with fire-rated floors and walls. The test measures:

• Movement capability of the joint system, including cycling
• Loadbearing capacity (where applicable)
• Ability to prohibit passage of flames and hot gases
• Transmission of heat through the system
• Hose stream resistance (for wall joints)

UL 2079 includes cycling tests that classify a joint as nonmoving or moving (for example, thermal, wind sway, or seismic movement). The movement class must match what the joint will actually experience.

Important limitation: The test does not provide quantitative information about smoke or gas leakage through the joint system. Where smoke resistance is required, UL 2079 L-rating data is used.

C. ASTM E2307 — Perimeter Fire Barriers

ASTM E2307 measures the perimeter fire barrier’s ability to maintain a seal during deflection and deformation of the exterior wall and floor assemblies. The test subjects the perimeter joint to:

• Fire exposure from an interior compartment fire
• Flame plume from a window burner below
• Movement of the wall and slab

Important limitation: The test does not measure flame spread over the exterior face, within combustible cores, or over interior surfaces. Those are addressed separately (see NFPA 285 and Article 133).

Key point: Each test standard addresses a specific condition. A joint system tested to ASTM E1966 is not a substitute for a perimeter fire barrier tested to ASTM E2307.

Key Article: Article 133 — Curtain Walls and Fire Safety Performance

Pro Tip: The T-rating is often misunderstood. It measures temperature rise on the unexposed side, not just flame passage. A system with an F-rating but no T-rating may still allow enough heat transfer to ignite materials on the non-fire side.

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◆ Section 4: When Each Rating Is Required (Code Triggers)

Selecting a system starts with knowing which ratings the code demands for the assembly being penetrated.

The IBC also allows limited prescriptive methods, for example small noncombustible items through concrete or masonry with a tight annular space filled with approved noncombustible material. These exceptions are narrow. Confirm the limits in the edition adopted by your AHJ before relying on them.

Key point: The F-rating, T-rating, and L-rating answer different questions: flame, heat, and smoke. Specify the ones the assembly actually requires.

Pro Tip: Put the required F, T, and L ratings on the penetration schedule for every condition. Installers cannot select a compliant system from a rating that is not stated.

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◆ Section 5: Components of a Listed System

A listed firestop system includes every component required to achieve the rating. The listing specifies each component, and substitutions void the rating.

Key point: The listing specifies not just the products but their arrangement, thickness, compression, and annular space limits. A system installed with the correct products in the wrong configuration is not a tested system.

Pro Tip: The UL Product iQ database and other listing directories (such as Intertek’s) provide installation requirements, drawings, and descriptions for each listed system. Require the contractor to provide the specific system listing for each penetration condition.

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◆ Section 6: Matching a System to the Field Condition

A listing is only usable when every variable in the field matches it. The following parameters must be checked together.

Annular Space, Backing, and Sealant Depth

These three parameters are where most firestop failures occur.

A. Annular Space. The annular space is the gap between the penetrant (pipe, cable, conduit) and the edge of the opening. Each listing specifies a permitted range.

B. Backing Material. Mineral wool or ceramic fiber backing is often required to support the sealant during installation and curing, provide insulation against heat transfer, and maintain the sealant at the required depth. The listing specifies the type, density, and compression of the backing material.

C. Sealant Depth. Sealant must be applied at the depth specified in the listing. A sealant applied too thin will not achieve the rating. The listing also specifies the required sealant type, and substituting a different product voids the system.

Key point: Inspectors verify annular space within permitted limits, backing material type and compression, and sealant depth that meets the listing.

Pro Tip: Photograph the installed system before it is concealed. This documentation is essential for special inspection records and future maintenance.

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◆ Section 7: Special Conditions That Cause Problems

Some conditions are repeatedly mishandled because the standard details do not fit them.

• Plastic pipe. Combustible pipe burns away in a fire, so the system must close the opening. Collars and wraps are typically listed for specific pipe materials, diameters, and wall thicknesses.
• Insulated pipe. Insulation may need to continue through the opening, or be removed and replaced by a listed material. Follow the listing.
• Cable tray and bundled cable. Fill ratio, tray type, and cable type affect the listing. Overfilled trays often fall outside the tested range.
• Duct penetrations. The damper listing governs the sleeve or angle. The firestop at the annular space must also match a listing.
• Head-of-wall and joint conditions. Movement class and joint width must match the E1966 / UL 2079 listing. Deflection at the top of a wall is a frequent failure point.
• Membrane penetrations. Outlet boxes and similar devices must follow the assembly listing or the prescriptive limits, including back-to-back spacing rules.
• Smoke barriers. The rating must address smoke passage, not just fire. Confirm the L-rating requirement.
• Curtain wall and perimeter conditions. Safing insulation and perimeter barrier systems must be tested to ASTM E2307, and mullion cavities are often left open.
• Abandoned and re-entered penetrations. Removing cables or adding new ones through an existing firestop breaks the seal unless it is restored.
• Temporary firestopping. During construction, openings may need temporary protection until the final system is installed. Plan this early, particularly on phased projects.

Pro Tip: Walk the building before ceilings close and look for the condition your standard details do not cover. That is where the problems are.

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◆ Section 8: Inspection Standards

Firestop inspection is governed by two ASTM standards, both referenced in IBC Chapter 17.

A. ASTM E2174 — Through-Penetration Firestop Systems

ASTM E2174 establishes procedures to inspect firestop products and systems, including methods for field verification. The practice is referenced in IBC Chapter 17, Special Inspections. It provides methods by which qualified inspectors verify that required firestops have been installed and that installations are in accordance with the inspection documents.

B. ASTM E2393 — Joint Systems and Perimeter Fire Barriers

ASTM E2393 establishes procedures to inspect fire-resistive joint systems and perimeter joint protection. The standard references ASTM E1966 and UL 2079 for joint systems and ASTM E2307 for perimeter joint protection. The practice provides methods by which qualified inspectors verify that required joint systems have been installed and that installations are in accordance with the inspection documents.

C. What Inspectors Verify

D. Special Inspection Under the IBC

IBC Chapter 17 requires special inspection of firestopping in many buildings. The trigger depends on the edition and on local amendments, and it commonly includes high-rise buildings and buildings assigned to Risk Category III or IV. Confirm the applicability and the subsection numbering in your adopted edition.

Special inspection is separate from the contractor’s own quality control. The inspector should be independent of the installer and qualified for firestop work. Inspection agencies typically demonstrate qualifications through third-party accreditation and trained personnel. Confirm what your AHJ and project specifications accept.

Key point: Inspection is not a formality. It is the mechanism that verifies the installed system matches the tested system.

Pro Tip: The International Firestop Council’s Inspector Pocket Guide provides step-by-step field inspection checklists and guidance for Engineering Judgments.

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◆ Section 9: Destructive Verification and Sampling

ASTM E2174 and E2393 are mostly visual inspection procedures, but they also provide for destructive verification, which is the sampling of installed systems to confirm the installation matches the listing.

A. What Destructive Verification Involves

• Removing a sample of the installed system
• Measuring annular space, sealant depth, and backing compression
• Comparing the installation to the listing
• Repairing the sampled location with the same listed system, and documenting the repair

B. When It Is Used

Destructive verification is applied when the inspection documents, project specifications, or the AHJ call for it. The scope and sampling frequency depend on the building’s risk category, height, and the AHJ’s requirements. Confirm early whether your project requires it.

Key point: Destructive verification is not punitive. It is the only way to confirm that concealed installations meet the listing. A system that looks correct on the surface may fail when measured.

Pro Tip: Coordinate destructive verification with the contractor and the AHJ before installation begins. Sampling locations should be selected to represent the range of conditions on the project, and the repair of each sampled location must be built into the scope.

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◆ Section 10: Documentation and Close-Out

Documentation turns a firestop installation into a facility asset.

A. What the Documentation Package Should Include

B. Labeling and Identification

Firestop systems should be tagged or labeled to identify the system used. This supports future maintenance and renovation work, and it allows inspectors to verify compliance after the fact.

Key point: The documentation package is not just for close-out. It is for the life of the building. When a future renovation penetrates a rated assembly, the documentation tells the contractor what system was used and how to restore it.

Pro Tip: Require the firestop contractor to organize the submittal by condition, not by product. A condition-based submittal matches how the work is actually installed and inspected.

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◆ Section 11: Maintenance, Alterations, and Re-Entry

The firestop program does not end at occupancy. Penetrations are altered more often than almost any other part of a building, especially cabling.

A. Owner Responsibility

The IFC places responsibility on the owner to maintain fire-resistance-rated construction, including penetrations and joints, in good repair. After a rated assembly is breached, the opening must be restored with a listed system. Verify the specific provisions in your adopted fire code.

B. Managing Alterations

• Require a penetration permit or work-order process so that no one cores or cuts a rated assembly without notifying facilities.
• Use the original documentation to identify the system that was installed.
• Restore each opening with a listed system that matches the new field condition.
• Update the penetration schedule, photographs, and labels after the work.
• Inspect the new work, and re-inspect existing systems the work may have disturbed.

C. Cabling and Re-Entry

Low-voltage and data cabling is the most frequent source of broken firestops. Options include:

• Listed pass-through devices designed for adding and removing cables
• Listed modular systems that can be re-opened and resealed
• Restoration of the original system after each cable change, performed by a trained installer

D. Periodic Review

A periodic walk-through of accessible rated assemblies, such as above-ceiling areas, shafts, and mechanical rooms, can find unprotected penetrations before an inspector or a fire does.

Key point: A firestop system that was compliant at turnover is only compliant today if every alteration since then was restored and documented.

Pro Tip: Require that the firestop contractor for any alteration work be qualified, even for small jobs. Small penetrations are where most unlisted repairs happen.

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◆ Section 12: Contractor Certification Programs

Two programs provide third-party verification of a firestop contractor’s quality management system.

A. UL Solutions Qualified Firestop Contractor Program

The UL Solutions Qualified Contractor Program is a quality management audit-based service for installers of firestop systems. To participate, a contractor must:

• Appoint and employ a Designated Responsible Individual (DRI) with applicable expertise
• Pass the UL Solutions Firestop Exam or NFCA industry exam
• Maintain a 10-element management system evaluated through an annual audit

The program covers review of project design and construction document requirements, installation, training and field quality, and documentation and record keeping. Qualified contractors are listed in the UL Solutions online certifications directory and can obtain a Master Audit Certificate of Compliance (MACC) for specific projects.

B. FM 4991 — Approval of Firestop Contractors

FM 4991 establishes requirements for approved contractors who install firestop systems. The standard is maintained by FM Approvals and is updated periodically (confirm the current edition on the FM Approvals website).

Key point: Both programs provide third-party auditing of a contractor’s training, methods, and documentation. Many specifications and some AHJs now require one of them, and they materially reduce inspection findings.

Pro Tip: When evaluating firestop contractors, ask for their UL or FM certification and the name of their DRI. The certification is a signal of quality management, not just technical knowledge.

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◆ Section 13: Engineering Judgments

Where field conditions deviate from tested listings, an Engineering Judgment (EJ) may be developed.

A. What an EJ Is

A firestop Engineering Judgment is a technical evaluation based on tested systems, engineering principles, and applicable guidance. It is intended to address specific firestop performance considerations and provide schematic, representative details.

B. What an EJ Is Not

The International Firestop Council (not to be confused with the International Fire Code, also abbreviated IFC) has issued a position statement clarifying that EJs are not:

• As-built drawings
• Coordination drawings
• Complete construction documents
• Code compliance evaluations for surrounding construction
• A substitute for the Registered Design Professional’s project responsibilities

C. Who Prepares EJs

EJs should be prepared by:

• The manufacturer’s qualified technical personnel
• A knowledgeable registered Professional Engineer
• A Fire Protection Engineer
• An independent testing agency

Key point: Use EJs only where no tested and listed system exists for the application. Many AHJs expect EJs to follow the International Firestop Council guidelines for evaluating firestop engineering judgments and to be submitted for review.

Pro Tip: Adding unnecessary detail to an EJ can create problems, including increased costs, delayed approvals, and confusion. Keep the EJ focused on the firestop condition being evaluated.

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◆ Section 14: Specifying and Coordinating Firestopping

Many firestop problems begin in the specification and the schedule, long before installation.

A. Specification

• Use a dedicated specification section (CSI MasterFormat Division 07, Firestopping, with joint firestopping often in its own section).
• Require listed systems only, with F, T, and L ratings stated.
• Require submittals organized by condition, with the listing for each.
• Require the contractor certification and inspection provisions covered above.
• Define who is responsible for firestopping each trade’s penetrations, so that no trade assumes someone else will do it.

B. Coordination

• Hold a pre-installation meeting with the firestop contractor, the trades, the special inspector, and the AHJ if required.
• Consider a mockup of representative conditions for early review.
• Sequence firestopping so that systems are installed and inspected before ceilings, insulation, and finishes conceal them.
• Coordinate with other trades whose work interacts with firestopping, including mechanical, electrical, plumbing, and low-voltage.

Pro Tip: Inspections that happen after concealment are expensive. Schedule firestop inspections as hold points before the work is covered.

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◆ Section 15: Design Checklist for Firestop Systems

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◆ Section 16: Common Mistakes and How to Avoid Them

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◆ Section 17: Conclusion

Firestop systems are where rated assemblies most often fail. The gap between the tested assembly and the installed assembly is where ratings are lost, and firestopping is the most common point of failure in that gap.

The testing standards (ASTM E814 / UL 1479 for penetrations, ASTM E1966 / UL 2079 for joints, and ASTM E2307 for perimeter barriers) define the systems. The inspection standards (ASTM E2174 and E2393) verify that installed systems match the listings. Contractor certification, documentation, and a disciplined alteration process close the loop and keep the system compliant long after turnover.

Firestopping is not a product. It is a system, and it is only as good as its installation and its maintenance.

Key Takeaways:

• Firestop systems are tested as complete systems, not individual products.
• ASTM E814 covers through-penetrations; ASTM E1966 covers joints; ASTM E2307 covers perimeter barriers.
• F-rating is flame passage; T-rating is temperature rise on the unexposed side; L-rating is air leakage and matters for smoke barriers.
• Specify the ratings the assembly actually requires, and state them on the penetration schedule.
• Annular space, backing material, and sealant depth are the three most common points of failure.
• ASTM E2174 and E2393 define inspection procedures for firestop and joint systems.
• IBC special inspection applies in many buildings, and destructive verification is used where the inspection documents or the AHJ call for it.
• Documentation turns a firestop installation into a facility asset.
• UL Qualified Firestop Contractor and FM 4991 provide third-party verification of contractor quality management.
• Engineering Judgments are technical evaluations, not as-built drawings.
• Every later alteration must be restored with a listed system and documented.

Take Action Today:

1. Prepare a penetration schedule organized by condition, with required F, T, and L ratings.
2. Select listed systems that match each field condition.
3. Verify annular space, backing, and sealant depth during installation.
4. Identify smoke barriers and confirm L-rating requirements.
5. Engage an approved inspection agency for ASTM E2174/E2393 inspections, and make inspection a hold point before concealment.
6. Plan destructive verification sampling and repairs with the AHJ.
7. Require a documentation package including listings, records, and photos.
8. Specify UL Qualified Firestop Contractor or FM 4991 certification.
9. Require Engineering Judgments only for unique conditions, prepared by qualified entities.
10. Set up a work-permit and re-entry process, and re-inspect after any alterations.

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What I changed, and what to verify

Added sections: code triggers for each rating (new Section 4), matching a system to the field condition (new Section 6), special conditions such as plastic pipe, cable tray, ducts, and head-of-wall (new Section 7), maintenance, alterations, and re-entry (new Section 11), and specifying and coordinating firestopping (new Section 14). I also added L-rating and W-rating, UL 2079 movement classes, smoke barrier penetrations (IBC §710), and duct and damper penetrations (IBC §717).

Corrected:

• Section 7 (now 9) said destructive verification is “required by IBC.” The IBC requires special inspection in certain buildings, and destructive sampling is applied per the inspection documents and the AHJ, so I reworded it.
• “IFC” is used for both the International Firestop Council and the International Fire Code. I spelled out the Firestop Council and flagged the overlap, since your other articles use IFC for the fire code.
• I removed the stray spaces before periods that were left by citation markers.

Please verify before publishing:

• The edition claims in the disclaimer (ASTM E814-26, E1966-24, E2307-25b) and the FM 4991 edition date. I changed the FM 4991 line to point readers to FM Approvals rather than state a date.
• The IBC Chapter 17 subsection numbers and the Risk Category III/IV and high-rise triggers for special inspection, which vary by edition.
• The exact T-rating exceptions and prescriptive limits in IBC §714, which I described in general terms.
• The UL contractor program details (DRI, 10-element system, MACC).
• Cross-reference article numbers (64, 131, 133) against your site.

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Continue Reading from Our Series:

• Related guide: Fire-Resistance-Rated Assemblies and UL Listings (Article 131)

• Learn more: Curtain Walls and Fire Safety Performance (Article 133)

• Read more: Firestopping and Penetration Sealing — Essential Details (Article 64)

IMPORTANT DISCLAIMER: This guide references the International Building Code (IBC), Chapter 7 (Fire and Smoke Protection Features), Chapter 14 (Exterior Walls), Chapter 17 (Special Inspections and Tests), and Chapter 26 (Plastic); NFPA 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components; ASTM E2307, Standard Test Method for Determining Fire Resistance of Perimeter Fire Barriers Using Intermediate-Scale, Multi-story Test Apparatus; and NFPA 101, Life Safety Code. These codes and standards vary by edition and are frequently amended by state and local jurisdictions. NFPA 285 has been published in multiple editions (including 2019 and 2023), and AHJ-adopted editions commonly lag behind the most recent published edition by one or more cycles. Section numbers, exceptions, and compliance paths in IBC Chapters 7, 14, and 26 have changed across editions, so verify every requirement against your AHJ-adopted edition. Local amendments and the edition adopted by your Authority Having Jurisdiction (AHJ) always control. This guide is a starting point only. Always verify the specific requirements applicable to your project with your local AHJ.

Curtain walls are non-structural exterior cladding systems that hang from the building structure. They are designed to resist wind, rain, and thermal movement, but their fire performance is a separate and equally critical design consideration. A curtain wall that performs perfectly in service can become a vertical fire spread path if its components and details are not properly evaluated.

Two test standards are central to curtain wall fire safety. NFPA 285 evaluates how the entire exterior wall assembly performs when an interior fire breaks out through a window opening. ASTM E2307 evaluates whether the perimeter fire barrier, the seal between the curtain wall and the floor slab, can maintain its integrity during a fire. Both are pass/fail tests, and both are assembly tests, not material tests. The IBC adds prescriptive provisions for perimeter fire containment, spandrels, and fireblocking that work together with these tests.

This article covers the regulatory framework, the testing standards, perimeter fire containment, spandrels and glazing, the risks posed by combustible components, design variations and listings, inspection and maintenance, retrofit considerations, and the lessons from major façade fires including First Interstate Bank and Grenfell Tower.

◆ Section 1: Why Curtain Walls Are Different

A curtain wall is not a fire-rated wall assembly in the traditional sense. It is a cladding system that hangs from the building structure and may contain combustible components: aluminum composite panels (ACP), foam plastic insulation, combustible water-resistive barriers, and laminated veneers.

Factor	Challenge
Non-structural	Curtain walls do not carry building loads; their fire performance is separate from structural fire resistance
Combustible components	Many modern curtain walls contain foam plastic insulation, ACP cores, or combustible WRBs
Perimeter joint	The void between the curtain wall and the floor slab is a potential fire spread path
Vertical spread	Curtain walls span multiple floors; fire can travel vertically through the assembly
Window openings	Interior fires that break through windows expose the exterior wall to flame
Glass and framing	Glass can fracture and fall out, and aluminum framing softens at relatively low temperatures

Key point: NFPA 285 is an assembly test. It evaluates how the entire wall system (cladding, insulation, WRB, sheathing, framing, and air cavities) performs when exposed to fire. A material that passes ASTM E84 (flame spread) does not automatically contribute to an NFPA 285 compliant assembly.

Key Article: Article 131 — Fire-Resistance-Rated Assemblies and UL Listings

Pro Tip: NFPA 285 is a pass/fail test, but the data it generates (temperatures at dozens of thermocouples throughout the assembly) is increasingly used for engineering analysis of design variations.

◆ Section 2: Regulatory Framework

Curtain wall fire safety is governed by a coordinated set of codes and standards.

Standard	Scope	Key Provisions
IBC Chapter 7	Fire and smoke protection features	Perimeter fire containment (§715.4); vertical separation of openings (§705.8.5); fireblocking (§718)
IBC Chapter 14	Exterior walls	Triggers for NFPA 285 testing; combustible WRB requirements
IBC Chapter 17	Special inspections	Inspection of fire-resistant joints and penetrations
IBC Chapter 26	Plastic	Foam plastic insulation in exterior walls; NFPA 285 requirement
NFPA 285	Exterior wall assembly fire propagation	Test method for vertical and lateral flame spread
ASTM E2307	Perimeter fire barrier	Fire resistance of the joint at the floor/wall intersection
NFPA 101	Life safety	Where adopted, governs egress, compartmentation, and building construction features; it does not replace the IBC or NFPA 285 façade provisions

Key point: The IBC establishes when NFPA 285 testing is required. NFPA 285 establishes how the test is conducted. The IBC also requires perimeter fire containment tested to ASTM E2307, and ASTM E2307 establishes how that joint is tested. Check which code family your jurisdiction has adopted, because NFPA 101 and the IBC are used in different places.

Key Article: Article 62 — Building Envelope Fire Safety — Design and Materials

Pro Tip: Recent IBC editions have expanded the ways of demonstrating NFPA 285 compliance, including approved engineering analysis based on tested assemblies. Confirm exactly which methods your adopted edition and your AHJ accept.

◆ Section 3: NFPA 285 — The Assembly Test

NFPA 285 evaluates the fire propagation characteristics of exterior wall assemblies containing combustible components.

A. What NFPA 285 Tests

The test is run on a two-story mock-up. A room fire is allowed to reach flashover and break out through a window opening, with a burner at the window exposing the exterior wall. Flame propagation is assessed:

• Vertically and horizontally across the exterior surface
• Within the assembly layers (through insulation, WRB, and cladding)
• Through air gaps and cavities
• From floor to floor

The test is pass/fail. Criteria include limits on how far flames spread vertically and laterally from the window opening, flames entering the second-story room, and temperature limits at thermocouples within the assembly. The test also generates extensive temperature data. Refer to the standard for the exact criteria.

B. When NFPA 285 Is Required

The IBC triggers NFPA 285 testing for exterior walls of Type I, II, III, or IV construction that are greater than 40 feet in height above grade plane and contain combustible components. The trigger applies when the exterior wall covering, insulation, or water-resistive barrier is combustible.

Common triggers include:

• Foam plastic insulation in the exterior wall
• Combustible water-resistive barriers
• Metal composite material (MCM) systems with combustible cores
• Exterior wall veneers or panels using combustible adhesives or cores (check the language in your adopted edition)

C. Exceptions

Exceptions exist where the combustible component is limited. For example, walls where the WRB is the only combustible component and the exterior covering is brick, concrete, stone, terra cotta, stucco, or steel may be exempt. The WRB must also meet heat release limits under ASTM E1354 testing to use the exception. Typical limits are on the order of 150 kW/m² peak heat release rate, 20 MJ/m² total heat release, and 18 MJ/kg effective heat of combustion, but verify the exact values and conditions in your adopted edition.

Key point: NFPA 285 is not required for every curtain wall. It is required when the wall assembly contains combustible components and exceeds the height threshold. A curtain wall with noncombustible cladding and no combustible insulation or WRB may not trigger the requirement. Sprinklers do not remove the requirement.

Pro Tip: Recent code editions allow compliance by an approved analysis based on a tested assembly. This lets subject-matter experts evaluate modifications to tested assemblies through fire science analysis, submitted to the AHJ for approval.

◆ Section 4: ASTM E2307 — Perimeter Fire Barriers

The perimeter fire barrier is the seal between the exterior wall assembly and the floor slab. It prevents fire from spreading from one floor to the next through the void at the floor/wall intersection.

A. What ASTM E2307 Tests

ASTM E2307 measures the perimeter fire barrier’s ability to maintain a seal to prevent fire spread during the deflection and deformation of the exterior wall assembly and floor assembly during a fire test. The test uses an intermediate-scale, multi-story apparatus and subjects the perimeter joint to:

• Fire exposure from an interior compartment fire
• Flame plume from a window burner below
• Deflection and deformation of the wall and slab as the fire develops

The result is reported as an F rating, in hours, based on the barrier’s ability to resist the passage of flame.

B. Test Conditions

The fire exposure conditions are those specified by the test method for the first 30 minutes, then conform to the ASTM E119 time-temperature curve for the remainder of the test.

C. What ASTM E2307 Does Not Measure

The test does not provide quantitative information about:

• Smoke or gas leakage through the perimeter fire barrier
• Flame spread over the exterior face of the assembly
• Spread of flame within the combustible core of sandwich panels
• Spread of flame over the interior surface

These are addressed by other test methods, notably NFPA 285 for exterior flame propagation.

D. E2307 Versus Joint System Tests

Perimeter fire barriers are not the same as joint systems tested to UL 2079 or ASTM E1966. Joint systems address movement joints within rated assemblies. The perimeter barrier at an exterior curtain wall is evaluated to E2307 because the exterior fire exposure and wall deflection are different. Do not substitute one for the other.

Key point: ASTM E2307 and NFPA 285 are complementary. ASTM E2307 evaluates the perimeter joint; NFPA 285 evaluates the entire wall assembly including vertical and lateral flame spread.

Pro Tip: The perimeter fire barrier is a critical detail that is often value-engineered out or improperly installed. It must be specified, inspected, and maintained.

◆ Section 5: Perimeter Fire Containment in the IBC (§715.4)

The IBC requires voids at the intersection of an exterior curtain wall assembly and a fire-resistance-rated floor or floor/ceiling assembly to be sealed with an approved system. The system must be tested to ASTM E2307 and provide an F rating for a period not less than the fire-resistance rating of the floor assembly. This is the code provision that makes E2307 mandatory, and it is distinct from the NFPA 285 trigger.

Key point: E2307 produces an F rating only. It does not produce an L (leakage) rating, so smoke sealing at the perimeter requires its own specification and detail.

Pro Tip: Check your adopted edition for exceptions and for any separate smoke-sealing language. Do not assume the F rating alone addresses smoke.

◆ Section 6: Spandrels and Vertical Separation of Openings (§705.8.5)

Windows stacked vertically are a fire path through the façade even with a perfect perimeter barrier. For buildings of more than three stories, the IBC generally separates vertically aligned openings that are close horizontally. The separation is a spandrel of at least 3 feet with a 1-hour fire-resistance rating, or a flame barrier projecting at least 30 inches from the wall. Buildings fully protected by an automatic sprinkler system under the applicable IBC provisions are generally exempt, but verify the exceptions and the horizontal distance criteria in your adopted edition.

Key point: Spandrel areas are where perimeter safing, backpan insulation, mullion fireblocking, and the spandrel panel itself all meet. Coordinate them in a single detail rather than as separate trades.

◆ Section 7: Perimeter Barrier Details That Fail in the Field

The tested system is a specific combination of products, thicknesses, compression, and gap widths. Failures in the field commonly come from:

• Mineral wool safing that is not compressed to the tested percentage or not sized to the actual slab-edge gap
• Missing or incorrect mechanical support, such as impaling clips or angles called for in the listing
• Missing or wrong sealant or coating at the face, or a smoke seal that is omitted
• Unsealed mullion cavities, gaps at columns, and slab-edge irregularities
• Gaps wider than the tested range once building movement is accounted for
• Substituted products that void the listing

Key point: If the field condition is not covered by the listing, it is not a tested system.

◆ Section 8: Combustible Components in Curtain Walls

Many modern curtain walls contain combustible components that must be evaluated as part of the assembly.

A. Foam Plastic Insulation

Foam plastic insulation is common in curtain wall systems for thermal performance. The IBC requires foam plastic in exterior walls of Type I–IV construction to comply with Section 2603.5, which includes:

• A thermal barrier separating foam from the building interior (unless special approval)
• Potential heat limits (not exceeding that of the tested assembly)
• Flame spread and smoke-developed indices of 25/450 or less
• NFPA 285 compliance for vertical and lateral fire propagation

B. Aluminum Composite Materials (ACM/MCM)

ACM panels with combustible cores (often polyethylene) have been implicated in major façade fires. The IBC requires MCM systems containing foam plastic insulation to comply with Section 2603, including NFPA 285 testing. MCM also has its own provisions in Chapter 14.

C. Water-Resistive Barriers (WRB)

Combustible WRBs are a common NFPA 285 trigger. NFPA 285 is required when the WRB is combustible, unless the exception applies (WRB is the only combustible component with an approved noncombustible cladding).

D. Combustible Adhesives and Cores

Some veneers and panels use combustible adhesives to laminate a metal core with noncombustible facings. Check whether your adopted edition requires these systems to comply with NFPA 285.

Key point: The trend in code development has been to expand NFPA 285 triggers as new combustible components are introduced.

Pro Tip: When reviewing curtain wall submittals, verify every combustible component and whether it triggers NFPA 285. A single combustible WRB can trigger the requirement even if the cladding is noncombustible.

◆ Section 9: Vertical Fire Spread and the Stack Effect

Curtain walls can contribute to vertical fire spread through three mechanisms:

A. Combustible Core Spread

In ACM panels with combustible cores, fire can spread within the panel core from floor to floor, bypassing the perimeter fire barrier.

B. Cavity and Air Gap Spread

Air gaps and cavities within the curtain wall assembly can act as chimneys, drawing flames and hot gases upward. NFPA 285 specifically evaluates flame propagation through air gaps and cavities. At Grenfell Tower, the ventilated cavity and the combustible insulation worked together with the burning panels to accelerate spread.

C. Window-to-Window Spread

Flames leaving a window can lap up the exterior and enter the window above, especially when glass fails. This is addressed by spandrel and vertical separation provisions and by sprinklers, not by NFPA 285 or E2307 alone.

Key point: The perimeter fire barrier prevents spread through the floor/wall joint, but it does not prevent spread through the curtain wall assembly itself or between windows. NFPA 285 (assembly), ASTM E2307 (perimeter joint), and the IBC spandrel provisions are all needed.

◆ Section 10: Glazing and Vision Glass

Windows are where an interior fire exits the building. Glass fracture and fall-out expose the floor above to flame and can allow the fire to extend vertically even when the cladding is noncombustible.

• Annealed and some tempered glass can crack and fall out early; heat-strengthened and laminated glass may behave differently.
• Aluminum mullions soften at relatively low temperatures, which allows frame deformation and glass loss.
• Sprinklers near glazing can reduce glass fracture and flame exposure to the floor above.
• Fire-rated glazing is used where the IBC requires rated openings or rated spandrels.

Key Article: Fire-Rated Glazing: Types, Ratings, and Applications

Pro Tip: A rating on the glass is not a rating on the frame or the joint to the slab. Evaluate the complete system.

◆ Section 11: Design Variations, Listings, and Engineering Judgments

Tested assemblies are narrow. Changes to insulation type or thickness, panel size, attachment, cavity depth, or WRB can fall outside the test. Compliance options typically include:

• A direct test of the exact assembly
• A third-party listed assembly
• An approved engineering analysis or Engineering Judgment (EJ) based on tested assemblies

For any variation, document the reasoning, submit it to the AHJ for approval, and keep the record in the project file.

Key point: An EJ is only as strong as the test data and expertise behind it. Early AHJ engagement avoids late rejection.

◆ Section 12: Case Studies

A. First Interstate Bank Building, Los Angeles (1988)

This unsprinklered high-rise fire burned through several floors, spreading largely through the exterior. Glass broke and flames moved from window to window while fire also extended through the curtain wall. The case predates Grenfell and shows that perimeter joint performance, glass failure, and the lack of sprinklers drive vertical spread, not only combustible cladding.

B. Grenfell Tower, London (2017)

The Grenfell Tower fire in London on June 14, 2017, killed 72 people and led to a fundamental reassessment of façade fire safety worldwide.

What happened. The fire broke out in a fourth-floor apartment and spread rapidly up the building’s exterior. The cladding consisted of aluminum composite panels with a combustible polyethylene core, combined with combustible foam insulation and a ventilated cavity.

The inquiry findings. The Phase 2 report, published in September 2024, concluded that the fire resulted from decades of failure by government and industry bodies to address the danger of combustible materials in the external walls of high-rise residential buildings. The inquiry concluded that all deaths were avoidable.

Regulatory response. The fire led to:

• A ban in England on combustible materials in the external walls of new high-rise residential buildings above a set height (Scotland and Wales have separate rules)
• Enhanced oversight through the Building Safety Act 2022 and the Building Safety Regulator
• Global reevaluation of NFPA 285 compliance and façade fire safety

C. Other Façade Fires

Lacrosse Building (Melbourne, 2014) and The Address Downtown (Dubai, 2015) are widely cited examples of fires spreading over combustible panels and cladding.

Key point: Grenfell demonstrated that the consequences of non-compliant or inadequately tested façade systems are catastrophic. First Interstate demonstrated that even without combustible cladding, exterior and perimeter weaknesses can carry fire upward.

◆ Section 13: Construction, Inspection, and Maintenance

• IBC Chapter 17 special inspection of fire-resistant joints and penetrations. Verify the section number and scope in your edition.
• Inspect and photograph the perimeter barrier before it is concealed by ceilings, cladding, or other trades.
• Control fire risk during construction, when combustible façade materials may be exposed (see NFPA 241).
• Re-inspect after alterations. New penetrations, replaced panels, or added insulation can break compliance.
• Keep the tested assembly documentation, listings, and submittals as part of the building records.

◆ Section 14: Existing Buildings and Retrofit

Re-cladding, façade upgrades, and adding insulation can trigger NFPA 285 even if the original wall did not. Treat the new work as new construction and check the applicable existing-building code. For older high-rises, a façade fire audit is advisable, especially where ACM, foam insulation, or unlisted perimeter joints are suspected.

◆ Section 15: International Comparison

Many countries use different tests. The UK uses BS 8414 with BR 135 for external fire spread, Canada uses CAN/ULC S134, and Europe uses EN 13501-1 reaction-to-fire classes. They are not interchangeable with NFPA 285. Global projects should confirm which test the local authority accepts.

◆ Section 16: Design Checklist for Curtain Wall Fire Safety

Item	Status	Notes
Height threshold confirmed	☐	NFPA 285 triggered at >40 ft for Type I–IV construction with combustible components
Combustible components identified	☐	WRB, insulation, cladding core, adhesives
NFPA 285 compliance determined	☐	Direct test, listed assembly, or engineering analysis
ASTM E2307 perimeter barrier specified	☐	Tested system for floor/wall joint
IBC §715.4 perimeter containment	☐	F rating not less than floor rating
Spandrel / vertical separation of openings (§705.8.5)	☐	Spandrel or flame barrier, or sprinkler exception
Foam plastic insulation compliant	☐	IBC §2603.5: thermal barrier, potential heat, NFPA 285
MCM/ACM systems reviewed	☐	Core combustibility; NFPA 285 compliance
Perimeter fire barrier detailed	☐	Mineral wool, sealant, and attachment per listing
Mullion cavity fireblocking and spandrel safing	☐	IBC §718 and the tested system
Glazing fracture behavior and sprinkler coordination	☐	Window-to-window spread
Engineering Judgments documented	☐	If used for design variations
Special inspection records for perimeter joints	☐	IBC Chapter 17
AHJ coordination	☐	Early engagement on compliance path

◆ Section 17: Common Mistakes and How to Avoid Them

Mistake	Why It’s a Problem	How to Fix
Assuming NFPA 285 applies only to foam plastic	Combustible WRBs and adhesives also trigger	Identify all combustible components
Confusing NFPA 285 with ASTM E2307	Different tests, different purposes	Specify both where required
Using a UL 2079 joint system as a perimeter barrier	Different test and exposure	Specify an E2307 tested system
Using ASTM E84 Class A as sole basis	E84 is not an assembly test	Require NFPA 285 compliance for the assembly
Assuming sprinklers remove the need for NFPA 285	The trigger is construction type, height, and combustibles	Evaluate the trigger independently of sprinklers
Omitting perimeter fire barrier	Fire can spread through floor/wall joint	Specify ASTM E2307 tested system
Value-engineering out the perimeter barrier	Code violation; fire spread path	Include in base scope; inspect installation
Substituting safing or sealant on site	Voids the listing	Require the listed system and verify in the field
No engineering analysis for design changes	Compliance unverifiable	Document EJ and submit to AHJ
Ignoring combustible core in MCM	Vertical fire spread path	Verify core combustibility and NFPA 285 compliance
Not coordinating with AHJ	Delays; rejected submittals	Early engagement on compliance path

◆ Section 18: Conclusion

Curtain walls present unique fire safety challenges because they are non-structural cladding systems that often contain combustible components. NFPA 285 evaluates the entire wall assembly for vertical and lateral flame propagation. ASTM E2307 evaluates the perimeter fire barrier at the floor/wall intersection, and the IBC requires it. Spandrels, glazing, and fireblocking complete the strategy. All are needed.

The First Interstate and Grenfell fires showed two different ways façades fail: through exterior and perimeter weaknesses, and through combustible cladding that was never properly tested as an assembly. Façade fire safety cannot be assumed; it must be tested, detailed, inspected, and maintained.

Key Takeaways:

• NFPA 285 is an assembly test, not a material test; it evaluates the entire exterior wall system.
• NFPA 285 is triggered for Type I–IV construction over 40 ft with combustible WRBs, insulation, or cladding.
• ASTM E2307 evaluates the perimeter fire barrier’s ability to maintain a seal during fire and movement, and IBC §715.4 makes it mandatory with an F rating at least equal to the floor rating.
• E2307 does not address smoke leakage; smoke sealing needs its own specification.
• Spandrels, glass failure, and mullion cavities are fire paths even when the cladding is noncombustible.
• Combustible components (WRBs, foam insulation, MCM cores, and adhesives) trigger NFPA 285 requirements.
• Tested assemblies are narrow; design variations need listings or documented, AHJ-approved engineering analysis.
• Inspection during construction and re-inspection after alterations are essential to keep the system compliant.
• First Interstate shows fire spread without combustible cladding; Grenfell shows the catastrophic result of untested combustible façades.

Take Action Today:

• Determine whether your building triggers NFPA 285 (height and combustible components).
• Identify all combustible components in the curtain wall assembly.
• Verify NFPA 285 compliance through direct test, listing, or engineering analysis.
• Specify an ASTM E2307 tested perimeter fire barrier with the required F rating.
• Detail spandrels, safing, mullion fireblocking, and smoke sealing together.
• Verify foam plastic insulation compliance with IBC §2603.5.
• Document any Engineering Judgments and submit to the AHJ.
• Arrange special inspections and photograph the perimeter barrier before concealment.
• Coordinate with the AHJ early on the compliance path.

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Continue Reading from Our Series:

• Related guide: Fire-Resistance-Rated Assemblies and UL Listings

• Learn more: Building Envelope Fire Safety — Design and Materials

• Read more: How to Design Fire-Safe Building Envelopes

IMPORTANT DISCLAIMER: This guide references the International Building Code (IBC), Chapter 7 (Fire and Smoke Protection Features), specifically Section 716 (Opening Protectives), Table 716.1(1) (Markings) and Table 716.1(2) (Opening Fire Protection Assemblies by Wall Rating); IBC Section 2406 (Safety Glazing); NFPA 80, Standard for Fire Doors and Other Opening Protectives; NFPA 252, Standard Methods of Fire Tests of Door Assemblies; NFPA 257, Standard on Fire Test for Window and Glass Block Assemblies; UL 9, Fire Tests of Window Assemblies; UL 10B and UL 10C (door assembly tests); UL 1784 (air leakage tests of door assemblies); ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials; UL 263; 16 CFR 1201 (CPSC safety glazing); and ANSI Z97.1. These codes and standards vary by edition and are frequently amended by state and local jurisdictions. IBC Section 716 was Section 715 in the 2009 edition and earlier. Verify section numbers against your AHJ-adopted edition. Local amendments and the edition adopted by your Authority Having Jurisdiction (AHJ) always control. This guide is a starting point only. Always verify the specific requirements applicable to your project with your local AHJ.

Fire-rated glazing is one of the most misunderstood products in commercial construction. Unlike a fire door, which is a complete assembly with a single rating, glazing performance depends on two separate and independent characteristics: the ability to block flames and smoke, and the ability to block heat. A product can do the first without doing the second, and that distinction determines where it can be used.

The IBC and the test standards recognize two categories of fire-rated glazing: fire-protective (also called fire-protection-rated) and fire-resistive (fire-resistance-rated). Each has its own test standards, its own labeling system, and its own application limits. Confusing them, or relying on the fire endurance rating alone, leads to noncompliant installations that may pass a plan review but fail in a fire or at inspection.

This article covers the types of fire-rated glazing, the testing standards that govern them, the hose stream requirement, size and application limits, labeling, impact safety, frames and installation, and common field problems.

◆ Section 1: Why Glazing Ratings Are Different

A fire-rated wall is tested as a complete assembly under ASTM E119. It has one rating, and it either meets the acceptance criteria or it does not. Glazing is different because it is tested in different ways depending on what it must accomplish: as a window, as part of a door, or as part of a wall.

Characteristic	Fire-Protective Glazing	Fire-Resistive Glazing
Blocks flames and smoke	Yes	Yes
Blocks radiant and conductive heat	No	Yes
Test standard (windows, sidelights, transoms)	NFPA 257 or UL 9	ASTM E119 or UL 263
Test standard (as part of a door)	NFPA 252, UL 10B or UL 10C	ASTM E119 or UL 263, plus NFPA 252, UL 10B or UL 10C
Label marking	OH-XXX (windows); D-H-… (doors)	W-XXX; D-H-W-XXX (doors)
Typical rating range	20 to 180 minutes (varies by product and application)	20 to 120 minutes typical; some products listed higher
Area limit in fire windows	25% of the area of the common wall with any room	Not subject to the 25% limit
Where used	Doors, sidelights, transoms, fire windows in walls where windows are permitted	Fire barriers, fire partitions, shafts, exit enclosures and corridors where heat blocking or a higher rating is required

Note: Sidelights and transoms are evaluated as fire window assemblies (NFPA 257 or UL 9), not as part of the door leaf. Many products also carry a door listing (D-H-OH-XXX) so they can be used in either role.

Key point: Fire-protective glazing stops flames and smoke. Fire-resistive glazing does that and also blocks heat. A wall that must maintain a tenable environment on the non-fire side, or that is rated beyond what fire windows are allowed in, needs fire-resistive glazing, not fire-protective.

Key Article: Article 131 — Fire-Resistance-Rated Assemblies and UL Listings

Pro Tip: The fire endurance rating alone does not tell you whether a product is fire-protective or fire-resistive. A “60-minute” fire-protective glazing and a “60-minute” fire-resistive glazing are not interchangeable. Read the label and the listing.

◆ Section 2: Fire-Protective Glazing

Fire-protective glazing defends against the spread of flames and smoke for its designated fire rating. It does not block the transfer of radiant and conductive heat.

A. Test Standards

Standard	Application
NFPA 257 / UL 9	Fire window assemblies (windows, and sidelights and transoms where they are treated as windows)
NFPA 252	Fire door assemblies (glazing as part of the door)
UL 10C	Fire door assemblies, positive pressure test
UL 10B	Fire door assemblies, neutral pressure test (the IBC calls for positive pressure testing of doors, so check which method your adopted edition accepts)

B. Types of Fire-Protective Glazing

Type	Typical Rating	Appearance	Typical Applications
Specialty tempered	20 minutes	Optically clear, no wires	20-minute doors up to the maximum size tested
Specialty tempered, heat reflective	20–60 minutes	Clear, no wires	20–45 minute doors; 60-minute doors up to 100 sq in where limited; 45-minute sidelights and transoms
Specialty fire-protective	90 minutes	Clear, no wires	90-minute doors, generally limited to 100 sq in
Traditional wired glass	20–90 minutes	Annealed glass with embedded wire	Fire windows and transoms in non-hazardous locations; not a safety glazing product (see Section 8)
Safety wired glass	20–90 minutes	Wired glass with safety film	20–45 minute doors; 60–90 minute doors up to 100 sq in
Filmed safety ceramic	20–180 minutes (per listing)	Wire-free, slight tint	20–45 minute doors; 60–90 minute doors up to 100 sq in; higher ratings only in applications the code allows
Laminated safety ceramic	20–180 minutes (per listing)	Wire-free, slight tint	Same as filmed ceramic

Key point: A product may be listed for a rating or size that the IBC does not permit in a given application. Listing sets the ceiling; the code decides whether you may use it.

C. Area and Size Limits

Fire-protective glazing is limited by area in fire window assemblies and by size in doors.

• Fire windows. The total area of fire window assemblies is limited to 25 percent of the area of the common wall with any room (see the notes to Table 716.1(2)). This limit applies to fire windows, not to the vision panel in a door.
• Door vision panels. Limits depend on the door rating. See Section 5.
• Where fire windows are not permitted. Table 716.1(2) does not permit fire windows (fire-protective windows) in fire walls, in fire barriers rated more than 1 hour, or in shaft and exit enclosure walls. Fire-resistive glazing is the option in those walls.

Key point: The 25% limit exists because fire-protective glazing lets radiant heat through. The practical effect is that a mostly-glass wall would not provide the protection of a solid rated wall.

Pro Tip: For 60- and 90-minute doors in exit enclosures and exit passageways, fire-protective vision panels are limited to 100 square inches whether or not the building is fully sprinklered.

◆ Section 3: Fire-Resistive Glazing

Fire-resistive glazing provides the same defense against flames and smoke as fire-protective glazing, but it also blocks the transfer of radiant and conductive heat. It is tested as a wall assembly, so the label “W” means the glazing meets the wall-assembly criteria of ASTM E119 or UL 263.

A. Test Standards

• ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials
• UL 263, Fire Tests of Building Construction and Materials
• As part of a door assembly, also NFPA 252, UL 10B, or UL 10C
• Some applications and listings also include the hose stream test, which appears in the label (see Sections 4 and 6)

B. Where Fire-Resistive Glazing Is Used

Fire-resistive glazing is suitable where the code requires an assembly with a fire-resistance rating to enclose a space, and where fire windows are not permitted. Examples:

• Walls requiring a 1-hour or greater rating where fire windows are not allowed or the 25% limit would be exceeded
• Exit enclosure (stair) and shaft walls where a glazed wall lite is wanted
• Rated exit access corridors
• Fire barriers and fire partitions that need transparency

Because fire-resistive glazing blocks heat, it is not subject to the 25 percent area limit for fire windows.

C. Size Limits

Fire-resistance-rated glazing tested to ASTM E119 or UL 263 may be used in fire door assemblies up to the maximum size tested and in accordance with its listing. The 100 sq in limit that applies to fire-protective glazing in certain doors does not apply to it.

Key point: Fire-resistive glazing is the option when the code requires both separation and heat protection, or when the wall rating is too high for fire windows.

Pro Tip: Fire-resistive glazing is typically thick (multi-laminated, or with intumescent interlayers or gel) and carries a W marking on the label. Fire-protective glazing is typically thin and carries an OH marking (for windows) or D-H markings (for doors).

◆ Section 4: The Hose Stream Requirement

The hose stream test is one of the most misunderstood aspects of fire-rated glazing.

A. What the Hose Stream Test Is

Immediately after the fire exposure, the heated assembly is sprayed with water from a hose stream. This tests impact, erosion, and thermal shock, simulating the effect of sprinkler or fire department water on hot glass. In the U.S., the hose stream test is a pass/fail requirement for assemblies rated 45 minutes and longer. If the glass or framing fails, flames and smoke can spread. To earn a hose stream designation, the glazing and framing must remain in place and not break away.

B. The Hose Stream and Fire Door Assemblies

Condition	Hose Stream Required?
20-minute door assemblies in corridor walls or smoke barriers	No. Tested per NFPA 252 or UL 10C without hose stream
20-minute doors in other fire partitions (0.5-hour rating)	Yes. Tested with hose stream
45-minute and longer doors	Yes. Tested with hose stream
Sidelights and transoms in those same corridor and smoke barrier walls	Yes. They are treated as fire window assemblies, tested per NFPA 257 or UL 9, including hose stream

The corridor exemption applies to the door assembly only. Sidelights and transoms around that door are windows, not doors, and do not share the exemption.

C. Label Markings

Marking	Meaning
H	Glazing meets the hose stream requirements of NFPA 252, UL 10B, or UL 10C
OH	Glazing meets the fire protection and hose stream requirements of NFPA 257 or UL 9 (fire window assemblies)
NH	Older marking for glazing not meeting hose stream. You may still see it on older products; check the status in your adopted edition

Key point: The hose stream requirement is not universal. The code relaxes it for 20-minute door assemblies in corridors and smoke barriers, but not for the sidelights and transoms in the same wall.

Pro Tip: Glazing marked as meeting hose stream (H) may be used where hose stream is not required. The reverse is not true.

◆ Section 5: Size Limits in Door Vision Panels

The IBC limits the size of glazing in fire door vision panels based on the glazing type and the door rating.

A. Fire-Protective Glazing in Doors

Door Rating	Fire-Protective Glazing Size
20 minutes	Up to the maximum size tested
45 minutes	Up to the maximum size tested
60 and 90 minutes	100 sq in maximum in exit enclosures and exit passageways, whether or not the building is sprinklered; elsewhere per §716 and the listing
180 minutes	Generally not permitted. Confirm the limited exceptions (such as certain horizontal exit doors) in your adopted edition

B. Fire-Resistive Glazing in Doors

Fire-resistance-rated glazing larger than 100 sq in is permitted in fire doors when it is tested to ASTM E119 or UL 263 and to NFPA 252, UL 10B, or UL 10C, up to the maximum size tested and in accordance with its listing.

C. Sidelights and Transoms

Glazing in sidelights and transoms in corridors and smoke barriers is tested per NFPA 257 or UL 9, including hose stream. Fire-protective glazing is permitted only where fire windows are permitted for the wall rating (and within the 25% limit). Where the wall rating is too high for fire windows, such as fire barriers rated over 1 hour, fire-resistance-rated glazing is required.

Key point: The 100 sq in limit is a limit on fire-protective glazing in 60- and 90-minute doors in exit enclosures and exit passageways. Fire-resistive glazing tested as part of the door is not held to it.

Pro Tip: When reviewing plans, check the door rating before checking vision panel size. A large lite in a 20-minute corridor door may be fine; the same lite in a 90-minute stair door with fire-protective glazing is not.

◆ Section 6: Labeling and Identification

Every piece of fire-rated glazing must carry a permanent label showing the manufacturer, the test standard or listing, and the rating marking. The marking system is defined in IBC Table 716.1(1).

A. Marking Key

Symbol	Meaning
OH	Opening protective: meets the fire window requirements of NFPA 257 or UL 9, including hose stream
D	Glazing tested as part of a door assembly (NFPA 252, UL 10B or UL 10C)
H	Meets the hose stream requirement
T	Meets the temperature rise criteria (450°F rise at 30 minutes) used for certain exit enclosure and exit passageway doors
W	Meets the wall assembly criteria of ASTM E119 or UL 263 (fire-resistive glazing)
XXX	Rating period in minutes

B. Fire-Protective Glazing Markings

• OH-XXX: fire window assemblies (tested to NFPA 257 or UL 9, including hose stream)
• D-H-OH-XXX: glazing used in sidelights and transoms in certain corridor walls and smoke barriers that must also be tested to NFPA 252 because they are part of a door assembly
• D-H-XXX: glazing in fire door assemblies tested with hose stream
• D-H-T-XXX: glazing in doors that also meets the temperature rise criteria

C. Fire-Resistive Glazing Markings

• W-XXX: the glazing meets the wall assembly criteria of ASTM E119 or UL 263 for the rating period shown
• D-H-W-XXX: fire-resistive glazing in a door assembly tested with hose stream. For example, D-H-W-90 is a 90-minute fire-resistive glazing in a door assembly

Some glazing may carry an S marking when it is part of a smoke and draft control assembly (see Section 9).

D. Label Requirements

The label must be issued by an approved agency and permanently affixed to the glazing. It identifies the manufacturer, the test standard, and the marking.

Key point: The label is the compliance document. A missing, painted-over, or damaged label makes an otherwise compliant installation unverifiable. Inspectors check labels during plan review and field inspection.

Pro Tip: A quick way to read a marking: OH = opening protective (fire window), D = door, H = hose stream, T = temperature rise, W = wall (fire-resistive), XXX = minutes.

◆ Section 7: Common Applications

A. Corridors

Corridor ratings are set by IBC Table 1020.2. In many sprinklered buildings the corridor rating is 0 hour, so rated glazing is not needed at all. Where a corridor wall is rated (typically 1 hour, or 0.5 hour in some cases), Table 716.1(2) governs:

• Doors are typically 20 minutes, with the corridor exemption from the hose stream test described in Section 4.
• Sidelights, transoms and windows must be fire windows (tested to NFPA 257 or UL 9, with hose stream) within the permitted rating and the 25% area limit, or fire-resistive glazing.

Fire-resistive glazing is a design choice where a larger glazed area or greater visual openness is wanted, or where the wall rating is too high for fire windows. It is not a general requirement for exit access corridors.

B. Stairwells and Exit Enclosures

Exit enclosures are rated fire barriers (1 hour or 2 hours depending on the number of stories connected). In these walls:

• Doors: a 60-minute or 90-minute door may have a fire-protective vision panel, limited to 100 sq in. Larger vision panels or a more open look need fire-resistive glazing tested as part of the door.
• Walls: fire windows (fire-protective glazing) are not permitted in exit enclosure walls. A glazed wall lite in a stair enclosure must be fire-resistive glazing (W).
• Temperature rise: in buildings that are not sprinklered throughout, doors in exit enclosures and exit passageways must also meet the temperature rise (T) criteria. Radiant heat on the egress path is the reason.

C. Fire Barriers, Fire Partitions and Shafts

• Fire barriers rated 1 hour or less may use fire windows within the Table 716.1(2) limits and the 25% area limit.
• Fire walls and fire barriers rated more than 1 hour do not permit fire windows. Use fire-resistive glazing.
• In fire doors in fire walls and 3-hour barriers, fire-protective vision panels are generally not permitted, with limited exceptions such as certain horizontal exit doors. Confirm in your adopted edition.

D. Exterior Walls

Fire windows (OH) may be used in exterior walls where opening protectives are required. Exterior wall openings are also limited by fire separation distance and maximum area of openings under IBC Section 705.8, and fire-resistive glazing may be used where the wall itself must be rated.

E. Atriums and Large Spaces

Atrium separation under IBC Section 404.6 may be provided by a 1-hour fire barrier or, in some cases, by glass walls with sprinkler protection. Fire-resistive glazing is one way to build a transparent fire barrier that keeps the visual connection between floors. Sprinkler-based glass walls rely on the sprinkler design, so coordinate with the fire protection engineer.

Key point: The application determines the glazing type. A stair enclosure wall lite needs heat blocking. A corridor vision panel may need nothing, or only a fire window, depending on the wall rating.

◆ Section 8: Impact Safety and Safety Glazing

Fire rating is only half of the compliance picture. Glazing in doors, sidelights near doors, and other hazardous locations must also meet the safety glazing requirements of IBC Section 2406 and the impact standards 16 CFR 1201 (CPSC) or ANSI Z97.1.

• Traditional wired glass does not meet the impact safety requirements for hazardous locations. It is limited to locations where safety glazing is not required, and some jurisdictions (for example, for school buildings) restrict it further.
• Safety wired glass and specialty tempered, ceramic and laminated products are available with impact safety ratings and are the usual choice for doors, sidelights, and glazing near floor level.
• Fire-resistive glazing assemblies must also be checked for impact safety category where they are in hazardous locations.

Key point: A product can be fully compliant for fire and noncompliant for impact. Check both listings.

Pro Tip: Ask for two documents for every glazing product: the fire listing and the safety glazing certificate.

◆ Section 9: Frames, Systems and Installation

Fire-rated glazing is not rated alone. The rating belongs to a tested system: glass, frame, glazing bead, tape, gasket, and anchorage as listed.

• Use the listed frame. Fire-rated glass in a frame that is not listed for it voids the rating. Fire-resistive glazing in particular is often tested in specific frame profiles.
• No field modification. Do not cut, drill, or re-notch labeled glass, or change beads, tapes, or sealants without a listing that allows it.
• Install per NFPA 80 for doors and opening protectives, and per the manufacturer’s installation instructions and listing.
• Smoke and draft control. Where the door or window must also resist smoke passage (for example, smoke barriers), the assembly is tested per UL 1784 and carries an S marking. Make sure the glazing system is part of that listing.
• Inspection. NFPA 80 requires fire door assemblies to be inspected and tested after installation and at least annually. Include glazing, labels, and frames in that review: look for cracks, missing beads, painted labels, and film or signage applied over the glass.

Key point: If the frame, beads, or installation do not match the listing, the glass rating does not apply.

◆ Section 10: Existing Buildings and Replacement Glass

• Legacy wired glass. Existing buildings often have wired glass that is still permitted where it was legally installed. Replacement is often required where it is in a hazardous location or when the area is altered. Check the International Existing Building Code and local rules.
• Unlabeled glass. Without a label, the glass cannot be treated as rated. It must be replaced with labeled product or verified by the AHJ.
• Broken glass. Replacement glass must match the original listing, including the rating, the frame system, and the size limits. A clear replacement pane that looks the same is not enough.
• Films and coatings. Do not apply film to rated glass unless the manufacturer’s listing allows it.

◆ Section 11: Selection and Cost Considerations

Fire-resistive systems are heavier, thicker, and several times more expensive than fire-protective glazing in many cases, and they need specific frames. Fire-protective glazing is lighter and cheaper, but is limited by area, size, and rating.

Factor	Fire-Protective	Fire-Resistive
Relative cost	Lower	Higher
Weight and thickness	Thin, lighter	Thick, heavier
Frames	Standard listed fire frames	Often specific listed frames
Area limits	25% in fire windows	None from the 25% rule
Best for	Door vision panels, limited sidelights and transoms, fire windows in lower-rated walls	Walls over 1 hour, stair enclosures, large glazed walls, heat protection

Pro Tip: Decide early. Changing from fire-protective to fire-resistive late in design often changes frame, wall thickness, and budget.

◆ Section 12: Design Checklist for Fire-Rated Glazing

Item	Status	Notes
Required wall rating determined	☐	Per IBC Table 716.1(2) and the wall rating tables
Fire windows permitted for this wall?	☐	Not in fire walls, barriers over 1 hour, or exit enclosure and shaft walls
Glazing type selected	☐	Fire-protective or fire-resistive
Test standard confirmed	☐	NFPA 257/UL 9 (windows); NFPA 252/UL 10C (doors); ASTM E119/UL 263 (resistive)
Hose stream requirement determined	☐	Based on door rating, wall type, and whether it is a door, sidelight or transom
Door vision panel size verified	☐	By door rating and location; 100 sq in for 60/90-minute exit enclosure doors
Window area limit verified	☐	25% of common wall area for fire windows
Temperature rise needed?	☐	Exit enclosure and exit passageway doors in non-sprinklered buildings
Label marking confirmed	☐	OH-XXX, D-H-OH-XXX, D-H-T-XXX, W-XXX, D-H-W-XXX
Impact safety confirmed	☐	IBC §2406; 16 CFR 1201 or ANSI Z97.1
Frame listed for glazing	☐	Frame, beads, tape and anchorage as listed
Smoke and draft control considered	☐	UL 1784 and S marking where required
Installation per NFPA 80	☐	For doors and opening protectives
Label verification at closeout	☐	Permanent label present and legible

◆ Section 13: Common Mistakes and How to Avoid Them

Mistake	Why It’s a Problem	How to Fix
Assuming all “fire-rated glass” is the same	Protective and resistive are different	Verify label and test standard
Using fire-protective glazing as a stair enclosure wall lite	Fire windows are not permitted there and it does not block radiant heat	Use fire-resistive glazing (W)
Applying the 100 sq in limit to every door	Not every door rating has that limit	Check by door rating and location
Allowing oversized fire-protective glazing in 60/90-minute exit enclosure doors	Code violation	Limit to 100 sq in or use fire-resistive glazing
Ignoring the 25% limit for fire windows	Code violation	Calculate wall area and window area
Assuming sidelights share the door’s hose stream exemption	They are tested as windows	Test per NFPA 257 or UL 9 with hose stream
Rated glazing where the corridor is 0 hour	Unneeded cost	Check Table 1020.2 before specifying
Using wired glass in hazardous locations	Fails impact safety	Use safety-rated glazing
No permanent label on glazing	Compliance cannot be verified	Require labeled product; inspect at closeout
Unlisted frame with listed glazing	Assembly not listed	Match frame and glazing listings
Field cutting or modifying rated glass	Voids the listing	Order to size; no field modification
Confusing T (temperature rise) with W (wall)	Different performance criteria	T = temperature rise for doors; W = fire-resistive glazing
Replacing broken glass with a lookalike	Rating lost	Match the original listing

◆ Section 14: Conclusion

Fire-rated glazing is not a single product. It is two distinct categories with different performance characteristics and different applications. Fire-protective glazing stops flames and smoke but does not block heat. Fire-resistive glazing does both, and is required where the code demands protection from radiant heat as well as fire separation, or where the wall rating is beyond what fire windows are allowed in.

The hose stream requirement, size limits, labeling, impact safety, and installation all flow from that basic distinction. Getting the category right is the first step. Verifying the listing, the label, the frame, and the installation is the rest.

Key Takeaways:

• Fire-protective glazing blocks flames and smoke but not heat; it is tested to NFPA 257 or UL 9 as a window and NFPA 252 or UL 10C as part of a door.
• Fire-resistive glazing blocks flames, smoke and heat; it is tested to ASTM E119 or UL 263.
• Fire windows (fire-protective glazing) are limited to 25% of the common wall area and are not permitted in fire walls, barriers over 1 hour, or exit enclosure and shaft walls.
• Hose stream is required for 45-minute and longer ratings and for 20-minute doors outside corridors and smoke barriers; 20-minute corridor door assemblies are tested without it, but sidelights and transoms in the same walls are not.
• In doors, the 100 sq in limit for fire-protective glazing applies to 60- and 90-minute doors in exit enclosures and exit passageways; 20- and 45-minute doors allow up to the maximum size tested.
• Label markings tell the story: OH-XXX for fire windows, D-H-OH-XXX for door sidelights and transoms, D-H-T-XXX for temperature rise doors, W-XXX for fire-resistive.
• Safety glazing (IBC §2406) is a separate compliance check from fire rating.
• The rating belongs to the tested system: glass, frame, beads, and installation must match the listing.

Take Action Today:

• Determine the required wall rating and whether fire windows are permitted for it.
• Select fire-protective or fire-resistive glazing accordingly.
• Verify the test standard, hose stream requirement, and label marking for the application.
• Confirm door vision panel size by door rating and the 25% limit for fire windows.
• Check impact safety for hazardous locations.
• Specify listed frames and prohibit field modification.
• Verify installation per NFPA 80, and check labels at closeout.

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Continue Reading from Our Series:

• Related guide: Fire-Resistance-Rated Assemblies and UL Listings (Article 131)

• Learn more: Fire Door Requirements and Regulations for Commercial Buildings (Article 16)

• Read more: Curtain Walls and Fire Safety Performance (Article 133)

IMPORTANT DISCLAIMER: This guide references ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials; UL 263 (ANSI/UL 263); the International Building Code (IBC), Chapter 7 (Fire and Smoke Protection Features); and the UL Fire Resistance Directory. Codes and standards vary by edition and are frequently amended by states and localities. ASTM E119-26 is the current edition of the test method, but the edition adopted by your jurisdiction may be older. UL 263 is harmonized with ASTM E119. NFPA 251 was withdrawn as an active standard. Local amendments and the edition adopted by your Authority Having Jurisdiction (AHJ) always control. This guide is a starting point only. Always verify requirements with your AHJ.

Edition note: Section numbers in this guide follow the IBC as renumbered starting with the 2012 edition. Readers working with the 2009 IBC or earlier will find most Chapter 7 sections numbered one lower (for example, opening protectives were IBC 715, now 716; fire barriers were 706, now 707; smoke barriers were 708, now 709). Fireblocking and draftstopping are consolidated at IBC 718 in current editions.

Fire-resistance-rated assemblies are the backbone of passive fire protection. They slow fire spread, protect structural elements, and compartmentalize buildings. Unlike active systems such as sprinklers, alarms, and suppression, rated assemblies have no moving parts and need no power. They work by design, and they fail when construction deviates from the tested listing.

That is the core challenge: the rating belongs to the assembly as tested, not to its individual components. A wall rated for 2 hours holds that rating only if every component matches the listing: gypsum board type and thickness, stud gauge and spacing, fastener type and spacing, and insulation. Substitute one component without a sound basis, and the rating is in doubt.

This article covers testing standards, UL listings, how ratings are established, restrained vs. unrestrained classification, and the field verification that determines whether a rated assembly performs as designed.

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◆ Section 1: Why Fire-Resistance Ratings Matter

Key point: Fire-resistance ratings are expressed in hours (commonly 1, 1½, 2, 3, 4) and represent the time an assembly withstands the standard test exposure while meeting the applicable acceptance criteria. Those criteria depend on the assembly type (see Section 2).

Key Article: Article 45 — Occupancy Separation Requirements (NFPA 101 Table 6.1.14.4.1)

Pro Tip: The rating is not a prediction of how long the assembly will survive a real fire. It is a comparative measure under standard test conditions. Applying test results to actual buildings requires evaluating actual conditions.

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◆ Section 2: Testing Standards

A. ASTM E119 / UL 263

ASTM E119 is the primary test method for fire-resistance testing of building construction. UL 263 is the harmonized UL counterpart, and the two are used interchangeably in the IBC.

The test follows a standard time-temperature curve:

The test evaluates:

• Heat transmission through the assembly (temperature rise on the unexposed side)

• Structural load-carrying capacity during exposure (for loadbearing assemblies)

• Integrity (passage of flames or hot gases, ignition of cotton waste)

• Hose stream resistance (applied to walls and partitions, not to every element type). The hose stream is applied immediately after the fire exposure period, on the same specimen or a duplicate depending on the rating and the standard’s requirements. For some higher ratings or element types, the stream is applied to a duplicate (unexposed) specimen per the standard’s conditioning rules, which is why some listings show separate fire and hose-stream ratings. Readers frequently assume the same specimen takes both.

For walls and floors, the typical temperature criteria are an average rise of 250°F (139°C) on the unexposed surface, with a 325°F (181°C) rise at any single point. Columns and beams are judged mainly on load-carrying capacity and steel temperature limits rather than unexposed-surface rise.

B. NFPA 251

NFPA 251 was the NFPA fire endurance standard. It was withdrawn in Fall 2010, and ASTM E119 / UL 263 are the primary methods.

C. What the Test Does Not Measure

The test does not assess suitability under conditions other than the standard fire, and it does not predict performance after fire exposure. Real fires vary in fuel load, ventilation, and compartment size. Fire testing is a comparative tool, not an absolute predictor.

Key point: The test standard and the listing are different things. ASTM E119 defines the test. The UL Fire Resistance Directory publishes the specific assemblies that passed and the construction details required.

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◆ Section 2D: Fire Metrics That Are NOT Fire-Resistance Ratings

Three fire-performance measures are routinely confused with hourly ratings. Confusing them produces noncompliant construction even when every product is “rated” for something.

Key point: Interior finish, roof covering, and fire resistance are three independent compliance tracks. A corridor wall with Class A paint but no listed assembly is still unrated; a roof with a Class A membrane over unprotected structure may still need a rated deck and supports.

Pro Tip: When reviewing submittals, watch for datasheets that lead with an ASTM E84 or UL 790 classification as if it were a fire-resistance rating. Vendors do this constantly with coatings, insulation facings, and single-ply membranes.

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◆ Section 2E: Other Fire Curves and International Equivalents

The ASTM E119 curve is a cellulosic curve, developed for ordinary combustible building contents. Structures exposed to flammable-liquid pool fires are evaluated against the UL 1709 hydrocarbon curve, which rises far faster. An E119 rating does not substitute for a UL 1709 rating in petrochemical or fuel-handling structures, and vice versa.

International equivalents include ISO 834 (cellulosic curve, near-identical to E119), EN 13501-2 classifications (EI ratings), BS 476 Parts 20–22 (largely superseded but still cited on legacy documentation), and CAN/ULC S101 under Canada’s National Building Code. Ratings from one system are not interchangeable with another: an “EI 60” dossier does not automatically satisfy a 1-hour IBC requirement, and product listings must be matched to the jurisdiction’s adopted standard. Confirm equivalency with your AHJ.

◆ Section 3: How Fire-Resistance Ratings Are Established

IBC Section 703.3 recognizes several methods of establishing a rating [verify section numbers by edition]:

Listed designs are the most common route for practitioners and are the focus of this article. Prescriptive and calculated methods are useful for concrete and masonry, but they are not substitutes for listed assemblies where a listing exists for the application.

Fire-resistance rating vs. fire-protection rating: These are different. A fire-resistance rating applies to walls, floors, roofs, beams, and columns. A fire-protection rating applies to opening protectives such as doors, shutters, and windows (tested under NFPA 252, NFPA 257, UL 10B/10C), and fire dampers are tested separately (UL 555). An opening protective does not carry the wall’s fire-resistance rating, and the code sets how the two ratings relate.

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◆ Section 4: The UL Fire Resistance Directory

UL’s Fire Resistance Directory is a leading source of listed assemblies. Intertek also publishes listings, and the Gypsum Association’s Fire Resistance and Sound Control Design Manual (GA-600) collects gypsum-based designs.

A. Assembly Design Numbers

Each tested assembly has an alphanumeric design number. The prefix letter indicates the group of construction [verify against the current UL Guide Information]:

Note: The prefix letter is an organizational legacy, not a performance indicator. A “U” wall and a “W” wall of the same rating are not interchangeable, and some letter ranges (such as U/V/W) contain both loadbearing and nonbearing designs. The listing itself must always be read.

B. Finding the Right Design

UL Product iQ is the current tool for accessing UL fire-resistance designs. Registration is free. Listings are searched by design number, rating, or product category (BXUV is the key category for ANSI/UL 263 assemblies).

Key point: The design number is the specification. The assembly must be built as described, component by component, dimension by dimension.

Pro Tip: UL permits designers to transfer assembly specifications into construction documents. Check UL’s current terms of use.

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◆ Section 5: Assembly Components and Construction Requirements

A. Component Specificity

Each UL design specifies:

• Gypsum board: type, thickness, and number of layers

• Studs: size, gauge, spacing, and material

• Fasteners: type, length, and spacing

• Insulation: type, thickness, and density (where required)

• Protective materials: spray-applied fire-resistive materials (SFRM) and intumescent coatings, by type and thickness

Exception: UL General Information permits certain substitutions. For example, screws meeting ASTM C1002 or C954 may replace nails if head diameter, length, and spacing equal or exceed those specified, subject to the General Information conditions.

B. Gypsum Board Orientation

• Vertical application: long edges parallel to framing members.

• Horizontal application: long edges perpendicular to framing members.

Orientation and joint staggering are specified in the design and matter to the rating.

C. Gypsum Board Type

“Type X” and “Type C” boards are defined by ASTM C1396 and have specific fire-resistance properties. Many designs require a specific proprietary board, and not every Type X board qualifies. Verify the manufacturer, product, and thickness against the listing, including the board’s marking.

D. Minimums and Maximums

• Gypsum board thicknesses are minimums. Greater thickness is permitted if fastener length increases to give equal or greater penetration.

• Steel stud sizes are minimums unless otherwise stated.

• Stud spacing is a maximum unless otherwise stated.

• Metal thicknesses are minimums unless a specific gauge is indicated.

Key point: Know which dimensions are minimums, maximums, or exact.

Key Article: Article 64 — Firestopping and Penetration Sealing — Essential Details

Pro Tip: UL General Information allows additional gypsum layers in many wall designs, but not where a design restricts it, such as some floor-ceiling or loadbearing designs. Removing layers voids the rating.

E. Exposure Side

Many wall designs are rated for exposure from either side. Some designs are rated from one side only. For exterior walls, IBC Section 705 sets whether the wall must be rated for exposure from the inside only or from both sides, depending on fire separation distance. Exterior walls with a fire separation distance greater than 10 feet are rated for exposure from the inside only; walls with a fire separation distance of 10 feet or less must be rated for exposure from both sides.

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◆ Section 6: Restrained vs. Unrestrained Assemblies

The restrained/unrestrained classification applies to floors, roofs, and beams. It does not apply to walls or columns.

A. What Restraint Means

Restraint refers to whether the surrounding or supporting structure can resist the thermal expansion of the assembly during a fire.

• Restrained: supported by structure that resists thermal expansion, for example beams welded, riveted, or bolted to framing, or slabs cast with framing.

• Unrestrained: free to rotate and expand at its supports.

B. Why It Matters

A restrained classification can permit less fire protection for the same rating, often for steel beams and floors.

C. Determining the Classification

IBC §703.2.3 states that assemblies are not considered restrained unless the registered design professional furnishes evidence satisfactory to the building official. The restrained condition must be identified on the construction documents.

Sources for determining restraint:

• The restraint guidance in UL 263 and in the non-mandatory annex of ASTM E119 (historically Annex X) [verify annex designation by edition]

• UL Guide Information for Fire Resistance Ratings (BXUV)

Pro Tip: Many project specifications default to “unrestrained” in the rating schedule to avoid the documentation burden. That is a defensible practice, but it should be a deliberate, documented decision—not a silent default—because it typically increases the required protection thickness or rating.

Key point: When in doubt, use the unrestrained rating. It is more conservative and is valid where the assembly is actually restrained.

Pro Tip: Qualified listings often allow a lesser thickness of applied fire protection on steel if a restrained classification is confirmed.

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◆ Section 7: Walls, Floors, Roofs, and Columns

A. Wall and Partition Assemblies

Walls and partitions use prefixes U, V, and W. Key components are gypsum board layers, stud size, gauge, and spacing, fasteners, and insulation (optional in many wall designs unless specified).

The IBC groups rated vertical elements by function:

• Fire walls (IBC 706): structural stability required, since the wall must remain standing if construction on one side collapses

• Fire barriers (IBC 707): shafts, exit enclosures, occupancy separations

• Fire partitions (IBC 708): corridors, tenant separations, dwelling units

• Smoke barriers and partitions (IBC 709, 710): limit smoke movement, with separate rating and opening requirements

• Horizontal assemblies (IBC 711): floor and roof/ceiling separations

B. Floor-Ceiling Assemblies

Floor-ceiling designs use the A–L prefixes. Components include the structural floor (concrete, steel deck, or wood), the ceiling membrane (gypsum board or sprayed materials), and beams and joists.

Where the ceiling is part of the rated assembly, ceiling penetrations are part of the listing. Recessed light fixtures, air diffusers, and access panels must follow the listed design. Unprotected fixtures can break the membrane.

C. Roof-Ceiling Assemblies

Roof-ceiling designs use prefix P.

D. Column and Beam Protection

Column designs use prefixes X and Y, and beam designs use N and S. Common protection methods are:

• Spray-applied fire-resistive materials (SFRM)

• Intumescent coatings

• Gypsum board enclosures

• Concrete encasement

For protected steel, required thickness depends on the member’s W/D ratio, which is weight per foot divided by heated perimeter. Light, thin members heat faster and need more protection. SFRM listings also specify density and bond strength, which must be field-verified.

E. Mass Timber

Recent IBC editions added Type IV-A, IV-B, and IV-C construction. These rely on a mix of encapsulation, char calculations, and fire-resistance testing under ASTM E119. Rated mass timber should be evaluated with the designer and AHJ, using the adopted IBC edition.

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◆ Section 7F: Opening Protectives — Doors, Frames, and Glazing

Opening protectives are where most rating failures actually occur in finished buildings. Three ideas carry almost the entire topic.

1. Fire-protection ratings pair with wall ratings. The IBC (Chapter 716 in 2012+ editions; 715 in earlier editions) sets required door, shutter, and frame ratings as a function of the wall rating. Ratings are 20, 45, 60, 90, and 180 minutes. A common field error is installing a 20-minute door in a 1-hour stair enclosure because “it’s a rated door.” Specific pairings include:

Verify the pairing table against your adopted IBC edition.

2. Positive pressure vs. neutral pressure. Fire doors are tested to UL 10C (positive pressure), which superimposes a temperature-gradient neutral-plane requirement on the fire exposure; the older UL 10B (neutral pressure) legacy persists in some product literature. Specify UL 10C where the adopted code requires it [verify edition].

3. Fire-protective vs. fire-resistive glazing.

• Fire-protective glazing (tested to NFPA 257 / UL 9, with hose stream impact—Category A or B) stops flames but does not meet the temperature-rise criteria of ASTM E119. It is permitted only within size and application limits set by the IBC (for example, limited vision panels in certain 1-hour-or-less walls, and sidelights and transoms in 20-minute corridor walls). Hose-stream impact resistance (Category A vs. B) matters at locations subject to hose stream exposure.

• Fire-resistive glazing (tested to ASTM E119 / UL 263 as a wall or window assembly) can serve in higher-rated walls and larger areas, and its rating must equal or exceed the wall rating.

Key point: Glazing must carry a permanent label showing its rating, standard, and whether it passed the hose stream. Unlabeled or mislabeled “fire glass” in storefronts, borrowed lights, and corridor sidelights is one of the most-cited deficiencies in existing-building surveys.

Supporting details worth specifying:

• Temperature-rise doors. Doors in stair enclosures and certain other locations must limit heat transmission (T20/T250/T450 temperature-rise labels) so radiated heat does not block egress on the non-fire side [verify required locations by edition].

• Clearances and hardware. Typical limits: 1/8 inch or less at the head and jambs, 3/4 inch or less at the sill (less where smoke gasketing is required); positive latching; self-closing or automatic-closing; gasketing where required. No field drilling or welding beyond the listing.

• Labels. The door, frame, and glazing each carry labels. Missing, painted-over, or damaged labels make an otherwise compliant door unverifiable; NFPA 80 governs field labeling and inspection, with annual inspections required.

• Smoke doors. Governed by NFPA 105. They are leakage-rated (UL 1784), require closers and gasketing within stated limits, but—a frequent design error—do not require positive latching unless they are also fire doors.

• Fire-rated shutters and counter shutters follow the same pairing logic and are frequently missed in plans review for service counters and pass-throughs in rated walls.

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◆ Section 8: Penetrations, Joints, and Firestop Systems

Firestopping restores the rating where construction is interrupted. Each system type has its own test standard:

F rating vs. T rating: An F rating addresses flame passage only. A T rating also limits temperature rise on the unexposed side, and the IBC requires it for certain penetrations (for example, through-penetrations in floors with exceptions). An L rating (air leakage) matters at smoke barriers [verify the IBC section for your edition].

A listed firestop product does not create a compliant installation by itself. The field condition must match the applicable system listing.

Inspectors should verify:

• Annular space within permitted limits

• Backing material type and compression

• Sealant depth that meets the listing

• Devices and wrap strips positioned correctly

• Products that match approved submittals

Dampers: Where ducts penetrate rated assemblies, fire dampers (UL 555), smoke dampers (UL 555S), and combination dampers must be installed per the manufacturer’s instructions and listing. Ceiling radiation dampers (UL 555C) are used where ducts or openings pass through the ceiling membrane of a rated floor-ceiling or roof-ceiling assembly.

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◆ Section 8A: Membrane Penetrations and Electrical Work

Section 8 covers through-penetrations; membrane penetrations — breaches of only one side of a rated assembly — have their own rules [IBC 714.4 / 714.3 in 2012+ editions; verify by edition], and electrical trades create most of them.

Outlet and device boxes. Rules address metallic vs. nonmetallic boxes, aggregate area limits per wall area, and — the classic failure — boxes installed on opposite sides of the same stud cavity. Unless an approved putty pad or listed enclosure protects them, boxes on opposite sides of the wall must be adequately separated or protected per the code’s methods (commonly a horizontal offset). Electricians almost never know this rule.

Recessed luminaires. An “IC-rated” fixture is an insulation-contact rating, not a fire rating. Where the ceiling membrane is part of a listed floor-ceiling assembly, fixtures must be (a) covered by a listed fire-rated enclosure within the tested design, (b) protected by a listed recessed-fixture cover in a listed system, or (c) addressed in the UL design itself. Distinguish this from ceiling radiation dampers (UL 555C), which serve ducted openings.

Cabling and cable trays. Bundled cable through-penetrations require listed systems sized for the bundle; retrofit cable additions after occupancy are the single largest source of unrated penetrations in commercial buildings. Require the cabling work to be firestopped under the firestop contractor’s supervision, not as an afterthought.

Pro Tip: Put a note on the electrical drawings: “All boxes and fixtures in rated construction per Section X; opposite-side box offsets and putty pads by E-contractor; firestopping by certified firestop contractor.”

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◆ Section 8B: Fireblocking and Draftstopping Are Not Firestopping

Three similarly named requirements, three different purposes [IBC 718 in 2012+ editions]:

Key point: A Type V wood building typically needs all three. Fireblocking at wood framing is ordinary lumber or gypsum scraps installed per the code; it has nothing to do with UL systems. Plan reviewers reject permit sets that show rated walls but no fireblocking, and inspectors write it up constantly in multi-family wood construction.

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◆ Section 9: Field Verification and Common Failures

The gap between the tested assembly and the installed assembly is where ratings fail.

A. Common Deficiencies

B. Marking and Identification

IBC Section 703.7 requires fire walls, fire barriers, fire partitions, smoke barriers, and smoke partitions to be identified with signs or stenciling in concealed spaces [verify section number by edition]. Typical wording is “FIRE AND/OR SMOKE BARRIER — PROTECT ALL OPENINGS.” Placement and lettering size are specified by the code.

C. Special Inspection

IBC Chapter 17 requires special inspection of fire-resistant construction elements, including:

• Firestop penetrations and joints, required in high-rise buildings and Risk Category III and IV buildings

• Sprayed fire-resistant materials and mastic/intumescent coatings on structural members

ASTM E2174 covers on-site inspection of penetration firestops, and ASTM E2393 covers fire-resistive joint systems and perimeter fire barriers.

D. Engineering Judgments

Where field conditions deviate from tested listings, an Engineering Judgment (EJ) may be developed. EJs should be prepared by:

• Manufacturer’s qualified technical personnel

• A knowledgeable registered Professional Engineer

• A Fire Protection Engineer

• An independent testing agency

Key point: Use EJs only where no tested and listed system exists for the application. Many AHJs expect EJs to follow the International Firestop Council (IFC) guidelines for evaluating firestop engineering judgments and to be submitted for review.

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◆ Section 9E: Applied Fire Protection (SFRM/Intumescent) — Field Quality

Special inspection of SFRM (IBC 1705.14) covers three distinct verifications, and confusion among them causes disputes at substantial completion:

• Thickness — measured against the listing’s required thickness for that member’s W/D ratio, not a blanket number from the product data sheet. A beam with a different W/D than the drawing schedule carries a different required thickness.

• Density — ASTM E605; laboratory samples from in-place material.

• Bond strength — ASTM E736; bond and adhesion failures are the classic SFRM deficiency, especially on shop-applied primers, galvanized surfaces, or where cure conditions were poor.

Also verify: compatibility with shop primers, recoat and cure windows, moisture protection during construction (many cementitious products degrade when wetted before cure), required clips and anchors for cementitious SFRM on decks, and that any topcoat is specifically listed for use over that SFRM. “Equal” substitution of one listed SFRM for another is not permitted without a new listing or an accepted Engineering Judgment — this is a frequent attempted change order.

For intumescent coatings: required dry-film thickness per the listing, stripe coats on edges and flanges, and surface preparation per the manufacturer. DFT is checked with wet-film and cured-coating measurements; undocumented thinning is a known failure mode.

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◆ Section 9F: Firestop Program Quality

A listed product does not create a compliant installation — the corollary deserves its own treatment:

• Certified contractors. The UL Qualified Firestop Contractor Program and FM 4991 (Approval of Firestop Contractors) provide third-party auditing of a contractor’s training, methods, and documentation. Many specifications and some AHJs now require one of them, and they materially reduce inspection findings.

• Penetration schedule. Require the firestop submittal to be organized by condition (metallic pipe sizes, plastic pipe types and sizes, cable bundles, mixed penetrations, joints with movement), matching the project matrix — not a product cut-sheet dump.

• Inspection. ASTM E2174 (penetrations) and ASTM E2393 (joints and perimeter) define visual inspection and destructive verification (sampling of installed systems per the referenced sampling standard). Destructive verification is required by IBC special inspection provisions for firestopping in applicable buildings [verify edition and scope].

• Documentation. Tagged or labeled penetrations, photo records keyed to drawings, and red-lined as-builts turn the firestop package into a facility asset instead of a one-time inspection artifact.

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◆ Section 10: Maintenance and Alterations

Fire-resistance-rated construction must be maintained for the life of the building. The International Fire Code (IFC) requires owners to maintain it in conformance with the approved construction documents. Later work is a frequent cause of damage:

• New cabling or piping through rated walls and floors

• Removed ceiling tiles or cut-in fixtures

• Renovations that remove or relocate rated partitions

• Doors and frames altered or damaged. Fire doors must be inspected per NFPA 80, typically annually.

Pro Tip: Require trades to use listed firestop systems and to log each penetration. Re-inspect rated assemblies after major renovations.

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◆ Section 10A: Damage, Renovation, and Existing Buildings

Repair of rated construction must return the assembly to its listed condition. The IEBC addresses repairs and additions in existing buildings; a damaged 2-hour shaft wall patched with one layer of board is not a repaired 2-hour shaft wall.

After any fire or significant heat exposure, rated assemblies in the affected area should be assessed — gypsum degrades, SFRM can spall or delaminate, and intumescent coatings that have activated must be recoated per the manufacturer.

Pre-renovation survey. Before tenant improvements, document which walls are rated (the stenciling from IBC 703.7 exists for exactly this moment) and require the TI contractor to maintain a penetration log.

Close-out package. The owner’s operation and maintenance manual should contain the UL design numbers used, firestop systems by condition, special inspection reports, damper schedules and access details, and the NFPA 80 fire-door inspection reports. Buildings that hand over this package cost dramatically less to keep compliant.

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◆ Section 10B: Writing the Specification

Rating compliance is won or lost in the specification, not at inspection. Minimum content:

• Name the design numbers. “2-hour shaft wall” is not a specification; “UL Design U438 [or the applicable design], 2-hour, nonbearing, as detailed on drawings” is.

• Substitution clause. Only products and configurations included in the listed design are acceptable; “or equal” has no place in fire-rated work.

• Submittal requirements. Product data referencing the listing and the edition or revision of the listing (listings are revised — require the current revision unless a specific revision is frozen on the drawings).

• Special inspection statement. Identify the special inspections under IBC Chapter 17 (SFRM, firestopping in applicable occupancies, heights, and risk categories) and name the approved agency early.

• BIM coordination. Model rated zones; route MEP to avoid rated assemblies where possible and schedule every penetration that cannot be avoided. Every avoided penetration is a firestop system you will never have to inspect, maintain, or defend in a dispute.

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◆ Section 11: Design Checklist

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◆ Section 12: Common Mistakes and How to Avoid Them

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◆ Section 13: Conclusion

Fire-resistance-rated assemblies are the foundation of passive fire protection. They protect structure, contain fire, and protect egress paths. The rating belongs to the complete assembly as tested, and individual components are not interchangeable. The UL Fire Resistance Directory provides the specifications, and the assembly must be built as listed. Restraint classification can change the amount of protection required for floors, roofs, and beams. Field verification, especially of firestopping, determines whether the installed assembly will perform, and maintenance determines whether it keeps performing.

Key Takeaways:

1. ASTM E119 and UL 263 are the primary test methods for fire-resistance ratings.

2. The rating belongs to the complete assembly, not individual components.

3. UL design numbers are the specification, and the assembly must match.

4. Ratings can also be established by prescriptive or calculated methods.

5. Fire-resistance ratings and fire-protection ratings (opening protectives) are different.

6. Restrained vs. unrestrained affects floors, roofs, and beams, and IBC §703.2.3 requires it to be justified and documented.

7. Gypsum board thicknesses and stud sizes are minimums, and stud spacing is a maximum.

8. Every penetration and joint needs a listed firestop system.

9. Rated barriers must be marked, inspected, and maintained.

10. Engineering Judgments may be used only where tested systems are unavailable.

11. Door, shutter, and glazing ratings must pair with the wall rating; glazing must be matched to the application (protective vs. resistive, hose stream, size limits).

12. Fire resistance, flame spread, and roof covering classification are separate compliance tracks — never substitute one for another.

13. Fireblocking and draftstopping (IBC 718) are separate from firestopping; wood buildings need all three.

14. SFRM thickness is verified per member against the listing’s W/D-specific requirement, with density and bond-strength testing.

Take Action Today:

1. Determine the required fire-resistance rating for each assembly.

2. Select the design number from UL Product iQ or another listing source.

3. Specify all components exactly as listed.

4. Identify restrained/unrestrained classification on construction documents.

5. Coordinate ceiling fixtures, dampers, and opening protectives with the listings.

6. Select listed firestop systems for every penetration and joint.

7. Verify annular spaces and sealant depths during installation.

8. Engage special inspection where required.

9. Mark rated barriers and maintain them after alterations.

10. Document all Engineering Judgments with qualified professional review.

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Continue Reading from Our Series:

• Related guide: Occupancy Separation Requirements (NFPA 101 Table 6.1.14.4.1)

• Learn more: Firestopping and Penetration Sealing — Essential Details

• Read more: Fire Door Requirements and Regulations for Commercial Buildings