Technical Specifications

Achieving 2-Hour Fire Resistance Ratings with Cold-Formed Steel per ASTM E119

Cold-formed steel assemblies achieve 2-hour fire-resistance ratings through UL-listed configurations tested per ASTM E119, which evaluates structural integrity, temperature transmission, and hose stream resistance over a 120-minute standardized fire exposure. CFS is non-combustible per ASTM E136, contributing zero fuel load even if the gypsum fire barrier is breached.
  • 11-minute read
Who this article is for: Architects, structural engineers, fire protection engineers, and code consultants specifying 2-hour fire-rated CFS assemblies for mid-rise multifamily construction.

Technical guide to achieving 2-hour fire-resistance ratings with cold-formed steel per ASTM E119, covering test methodology, UL-listed assembly parameters, critical field details, and IBC compliance.

ASTM E119: Test Methodology and Acceptance Criteria

ASTM E119, “Standard Test Methods for Fire Tests of Building Construction and Materials,” is the foundational fire test standard referenced by IBC Section 703.2. The test subjects a full-scale assembly specimen to a standardized time-temperature exposure curve — reaching 1,000°F at 5 minutes, 1,700°F at 60 minutes, and 1,850°F at 120 minutes — and evaluates performance against three independent failure criteria.

Criterion Requirement Failure Mode
Structural Integrity Assembly sustains applied design load for full 120-minute exposure Structural collapse or inability to sustain load
Temperature Transmission Unexposed surface avg. rise ≤250°F; single point rise ≤325°F above ambient Excessive heat transfer through assembly
Hose Stream Assembly withstands 30-sec water application at 30 psi from 2.5-in. hose at 20 ft Water penetration or structural breach

These criteria are not negotiable. An assembly that fails any single criterion — structural collapse, excessive heat transfer, or hose stream breach — does not receive the rating.

UL-Listed 2-Hour CFS Assemblies

Wall assemblies are typically documented under UL Design No. H514 (and related H-series designs), achieving the 2-hour rating through multiple layers of Type X gypsum board on each face of the CFS stud wall. The gypsum layers serve as the thermal barrier, while the noncombustible CFS framing maintains structural integrity as the gypsum calcines during fire exposure.

Floor-ceiling assemblies incorporate CFS joists, multiple gypsum layers on the ceiling side, resilient channel for thermal break and acoustic isolation, and concrete or gypsum-concrete topping on the floor side. The ceiling membrane is the critical fire barrier, and the resilient channel attachment detail is essential to maintaining membrane integrity under thermal deflection.

Shaft wall assemblies — for elevator shafts, stairwell enclosures, and mechanical chases — are documented under UL Design Nos. D902 and D925 (and related D-series designs), using C-H stud configurations with multiple gypsum liner panels and face layers, achieving the 2-hour rating in a thinner profile than back-to-back stud walls.

Parameter Wall (UL H514-type) Shaft (UL D902/D925-type)
CFS Framing 3-5/8″ to 6″ studs, 20–16 ga., 16″ o.c. C-H stud, 25–20 ga., 24″ o.c.
Gypsum Layers 2 layers 5/8″ Type X each face 2 layers 1″ gypsum liner + 1 layer 5/8″ Type X face
Insulation 3-1/2″ mineral wool or fiberglass batts Typically none (air cavity)
Total Assembly Thickness ~8″ to 10″ ~4″ to 6″

Critical Design Considerations for 2-Hour Assemblies

Penetration firestopping is the most common source of fire-resistance failure in completed buildings. Every electrical box, conduit, pipe, and duct penetration through a fire-rated assembly must be firestopped with a UL-listed through-penetration firestop system (ASTM E814 / UL 1479).

Joint and gap treatment at assembly intersections — head-of-wall, wall-to-floor, wall-to-wall — requires listed joint systems per ASTM E1966 (UL 2079). The deflection gap at the top of CFS walls must accommodate structural movement while maintaining the fire barrier; slip-track and deflection connections must be designed to the UL listing requirements, not just structural criteria.

Screw pattern compliance is another area where field deviations create risk. The gypsum attachment pattern — screw spacing at edges versus field, screw type, minimum edge distance — is specified in the UL listing. Overdriven screws that break the gypsum face paper reduce pull-through resistance and can compromise membrane integrity under fire exposure.

IBC Code Compliance Pathway

IBC Table 601 establishes minimum fire-resistance ratings by construction type. Type I-A requires 3-hour primary structural frame and 2-hour floor construction. Type I-B and Type II-A both require 2-hour primary structural frame and 2-hour floor construction. These are the construction types most commonly specified for mid-rise multifamily (4–7 stories) where CFS framing is structurally viable.

IBC Section 703.2 permits fire-resistance ratings to be established through three methods: ASTM E119 testing, calculated fire resistance per Section 722, or prescriptive assemblies per IBC Table 722 series. For CFS assemblies, UL-tested configurations per ASTM E119 provide the most defensible compliance path — AHJs are most comfortable with tested assemblies because the performance data is empirical, not calculated.

Section 703.4 addresses nonsymmetrical assemblies — the fire-resistance rating applies to fire exposure from either side unless the assembly is specifically tested and listed for one-direction exposure only. This is particularly relevant for shaft walls, which are typically tested for fire exposure from the shaft side only.

Why CFS Outperforms Combustible Framing

The noncombustibility of cold-formed steel per ASTM E136 creates a fundamentally different fire risk profile compared to wood framing. In a fire-rated CFS assembly, the gypsum membrane provides the thermal barrier, and the steel framing behind it contributes zero fuel. If the gypsum membrane is breached — through a failed firestop, a construction defect, or fire exposure exceeding the rated duration — the CFS framing does not ignite. It may lose structural capacity at elevated temperatures (steel begins to lose strength above 1,000°F), but it does not add fuel to the fire.

Wood framing, by contrast, is combustible — even in fire-rated wood-frame assemblies with multiple gypsum layers, a membrane breach exposes fuel. For developers, architects, and engineers evaluating framing systems for mid-rise multifamily, the fire-resistance question is not just about achieving a code-required rating; it is about the margin of safety when things go wrong.

Frequently Asked Questions

What is the difference between a fire-resistance rating and a flame-spread rating?

A fire-resistance rating (per ASTM E119) measures how long an assembly — wall, floor, or shaft — resists fire passage and structural collapse, expressed in hours. A flame-spread rating (per ASTM E84) measures how quickly flame spreads across a material surface. They are different tests evaluating different characteristics. CFS achieves noncombustible classification per ASTM E136, a material-level test distinct from both.

Can CFS framing achieve a 2-hour fire-resistance rating without gypsum board?

No. Steel framing alone does not provide fire resistance because steel loses structural capacity at elevated temperatures. The 2-hour rating is a property of the complete assembly — CFS framing plus gypsum board layers, insulation, screws, and joint treatment. All components must match the UL-listed configuration to achieve the rating.

How do penetrations affect the 2-hour fire rating?

Every penetration through a fire-rated assembly — electrical, mechanical, plumbing — must be firestopped with a UL-listed through-penetration firestop system tested per ASTM E814 (UL 1479). Unfirestopped or improperly firestopped penetrations void the fire-resistance rating at that location.

What are the three ASTM E119 acceptance criteria for a 2-hour rating?

(1) Structural integrity — the assembly sustains its applied design load throughout the full 120-minute fire exposure. (2) Temperature transmission — unexposed surface average rise cannot exceed 250°F, with no single point exceeding 325°F. (3) Hose stream — the assembly must withstand a 30-second water application from a 2.5″ hose at 30 psi immediately after furnace exposure. Failure of any one criterion voids the rating.

References

  • ASTM International — ASTM E119, ASTM E136, ASTM E814, ASTM E1966, ASTM C840.
  • International Code Council — IBC 2021: International Building Code, Sections 703.2, 703.4, 722; Tables 601 and 722 series.
  • Underwriters Laboratories — UL Fire Resistance Directory: UL Design Nos. H514, M527, D902, D925.
  • American Iron and Steel Institute — AISI S100-16.
  • National Fire Protection Association — NFPA construction-site fire statistics.
  • Willis Towers Watson — 2023 industry loss data for wood-frame construction fires.

Ready to Specify 2-Hour Fire-Rated CFS for Your Project?

To discuss 2-hour fire-rated CFS assembly design, UL listing coordination, or fabrication scheduling for your Massachusetts multifamily project, contact our engineering team at nick@aacsteel.com or 617-560-0349. AAC Steel will produce a project-specific assembly recommendation based on your construction type classification, code requirements, and architectural intent.

About AAC Steel

AAC Steel is a cold-formed steel (CFS) framing company headquartered in Franklin, MA, founded by engineers and builders with two decades of experience on Northeast jobsites. The company designs, fabricates, and installs precision CFS structural systems — including PE-stamped engineering, BIM and shop drawings, and panelized fabrication — for 5+ story multifamily developments across Massachusetts, Rhode Island, and Connecticut.

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