Fire-Rated CFS Wall Assemblies: UL Design Guide for Multifamily Mid-Rise

AAC STEEL

Fire-Rated CFS Wall Assemblies: UL Design Guide for Multifamily Mid-Rise

Technical Reference for Architects, Specifiers & Structural Engineers

www.aacsteel.com

1. Executive Summary

Cold-formed steel framing provides architects and specifiers with a comprehensive library of UL-listed fire-rated assemblies — from 1-hour to 3-hour ratings — enabling mid-rise multifamily designs that meet IBC fire resistance requirements without the cost and schedule penalties of concrete or masonry fire barriers. For a 5-story, 60-unit multifamily project, selecting the right CFS fire-rated assemblies can eliminate 15-20% of the structural dead load compared to CMU demising walls while maintaining identical fire resistance ratings.

Fire-rated assembly selection is among the most consequential decisions in mid-rise multifamily design. The chosen assemblies dictate construction type eligibility under IBC Table 601, influence allowable building area per IBC Table 506, and determine whether the structural system can accommodate the required fire resistance ratings without resorting to cast-in-place concrete or masonry backup walls. For cold-formed steel framing, the UL Fire Resistance Directory contains hundreds of tested assemblies — but navigating those listings to find the assemblies that satisfy fire rating, structural capacity, acoustic performance, and constructability requirements simultaneously requires systematic analysis.

This guide provides architects, specifiers, and structural engineers with a structured reference for selecting CFS fire-rated assemblies in multifamily mid-rise construction. We cover IBC fire resistance requirements by construction type, explain the UL assembly designation system, detail the most commonly specified CFS wall and floor-ceiling assemblies with their UL Design Numbers and component requirements, address firestopping at penetrations, and identify Massachusetts-specific 780 CMR considerations. Every code reference cites the specific IBC section, table, or provision — because in fire-rated construction, precision is not optional.

2. IBC Fire Resistance Requirements for Mid-Rise Construction

The 2021 International Building Code establishes fire resistance rating requirements through two primary tables that govern every mid-rise multifamily project. Understanding these tables is the prerequisite for rational fire-rated assembly selection — every assembly choice flows from the construction type classification.

2.1 IBC Table 601: Fire-Resistance Rating Requirements for Building Elements

IBC Table 601 establishes minimum fire-resistance ratings for structural frames, bearing walls, floor construction, and roof construction based on construction type. For mid-rise multifamily CFS buildings, three construction types dominate the design conversation:

Type IIA Construction requires 1-hour fire-resistance-rated structural frame, 1-hour exterior and interior bearing walls, 1-hour floor construction, and 1-hour roof construction. All materials must be non-combustible per IBC Section 602.2. Cold-formed steel framing is non-combustible per ASTM E136, making it fully compliant as a Type IIA structural system. This is the most common construction type for 4- to 5-story CFS multifamily projects.

Type IIB Construction permits 0-hour (non-rated) structural frame, bearing walls, and floor construction when the building is fully sprinklered per NFPA 13. Materials must still be non-combustible. Type IIB enables significant cost reduction by eliminating applied fireproofing on structural elements, though fire-rated corridor walls and demising walls are still required by other IBC provisions (IBC Section 708 for dwelling unit separation, IBC Section 1020 for corridors).

Type IIIA Construction requires 1-hour exterior bearing walls of non-combustible materials, but permits combustible (wood) framing for interior elements with 1-hour ratings. CFS competes against wood framing in Type IIIA projects — and the non-combustible advantage of CFS is decisive: the structural frame contributes zero fire fuel load, unlike wood framing which is the fuel.

2.2 IBC Table 602: Exterior Wall Requirements

IBC Table 602 establishes fire-resistance ratings for exterior walls based on fire separation distance. At less than 5 feet separation distance, exterior walls require 1-hour rating with 0% openings. At 5 to 10 feet, 1-hour rating with 25% maximum openings applies. At 10 to 30 feet, the requirement reduces to 0-hour for non-combustible construction (Types I and II). CFS exterior wall assemblies using UL Design U425 series readily achieve 1-hour and 2-hour ratings with standard gypsum board and continuous insulation configurations.

2.3 Fire Walls, Horizontal Assemblies & Penetrations

IBC Section 706 governs fire walls used for area separation between buildings or building sections. Fire walls must extend from foundation to roof and maintain structural independence. For Group R occupancies (multifamily residential), IBC Section 706.4 requires fire walls to have a minimum 2-hour fire-resistance rating, though 3-hour ratings are required for Type I construction. CFS double-stud area separation wall assemblies achieve 2-hour and 3-hour ratings using tested UL assemblies.

IBC Section 711 addresses horizontal assemblies (floor-ceiling and roof-ceiling), requiring them to be continuous without openings except as permitted for shaft enclosures, vertical exit enclosures, and other specifically listed conditions. IBC Section 714 governs penetrations through fire-rated assemblies, requiring through-penetration firestop systems tested per ASTM E814 to maintain the fire-resistance rating of the assembly being penetrated. This is one of the most critical — and most commonly violated — requirements in fire-rated CFS construction.

2.4 The Non-Combustible Advantage

CFS framing is non-combustible per ASTM E136. This means the structural frame itself contributes zero fire fuel load to the building — a fundamental advantage over wood framing. In a fire event, CFS studs and joists do not ignite, do not contribute to fire spread, and do not generate combustion byproducts. The fire resistance of a CFS assembly depends entirely on the protective membrane (gypsum board layers) maintaining integrity for the rated duration. This is a quantifiable safety and insurance advantage that reduces fire risk by eliminating the single largest combustible element in wood-framed construction: the structure itself.

Key Benefits:

• Non-combustible structure per ASTM E136 — zero fire fuel load contribution from framing
• Full compliance with IBC Type IIA and IIB non-combustible requirements without additional fireproofing
• Broad UL-listed assembly library: 1-hour through 3-hour ratings available in tested configurations
• Lighter assemblies than CMU or concrete — reduced foundation loads by 15-25% on a typical 5-story project
• Faster erection cycle compared to masonry fire barriers — 30-40% labor savings on rated wall installation

3. Understanding UL Fire-Rated Assembly Designations

UL fire-rated assembly designations are the currency of fire-rated design — every architect and specifier must understand how to read them, what they certify, and how they relate to IBC compliance.

3.1 The ASTM E119 / UL 263 Standard Fire Test

Fire resistance ratings for building assemblies are determined by testing per ASTM E119 (Standard Test Methods for Fire Tests of Building Construction and Materials) or UL 263 (the UL equivalent). The test exposes the assembly to a standard time-temperature curve that reaches 1,000°F at 5 minutes, 1,700°F at 1 hour, and 2,000°F at 4 hours. The assembly must maintain structural integrity (for load-bearing assemblies), prevent flame passage, and limit temperature rise on the unexposed side to an average of 250°F above ambient. The duration the assembly meets all three criteria determines its hourly fire-resistance rating.

3.2 Reading UL Design Numbers

Each UL Design Number specifies every component of the tested assembly — stud size, gauge, spacing, gypsum board type, number of layers, fastener type and spacing, and insulation requirements. Any deviation from the tested configuration voids the listing. The assembly categories relevant to CFS multifamily construction are:

• U-series: Wall and partition assemblies. UL U400 through U499 series covers CFS-framed walls. Key listings include UL U425, UL U419, UL U423, and UL U411.
• L-series: Floor-ceiling assemblies. UL L500 through L599 series covers CFS joist floor-ceilings. Key listings include UL L524, UL L547, and UL L514.
• G-series: Roof-ceiling assemblies for CFS truss and joist roof systems.

3.3 Bearing vs. Non-Bearing Ratings

A critical distinction: bearing-rated assemblies are tested under load per ASTM E119 Section 8, while non-bearing assemblies are tested without applied load. A non-bearing 1-hour assembly cannot be used for a load-bearing wall without separate structural justification. Many UL U-series listings specify both bearing and non-bearing ratings; always verify the listing applies to the intended structural condition.

3.4 Tested Assemblies vs. Engineering Judgment

IBC Section 703.3 permits the use of engineering judgment to extend fire-resistance ratings beyond tested assemblies under specific conditions. Alternative methods include calculations per AISI S100 Appendix B (Fire) and analytical methods referenced in AISI S240 Chapter E. However, most authorities having jurisdiction (AHJs) strongly prefer directly listed UL assemblies. Engineering judgment should be reserved for conditions where no tested assembly exactly matches the design condition — not as a shortcut to avoid specifying a listed assembly.

Key Benefits:

• UL Design Numbers provide unambiguous, tested-and-listed fire resistance documentation
• Direct IBC compliance pathway — no engineering judgment debate with the AHJ
• AISI S100 and AISI S240 provide analytical backup when tested assemblies require modification
• Assembly listings include acoustic data (STC ratings) — enabling dual fire and acoustic compliance from a single reference

4. Key CFS Wall Assemblies for Multifamily

This section provides the technical core of this guide: the specific UL-listed CFS wall assemblies most commonly specified for multifamily mid-rise construction. Each assembly type includes UL Design Number references, stud specifications, gypsum board requirements, and achieved ratings.

4.1 Load-Bearing Exterior Walls

CFS load-bearing exterior walls in mid-rise multifamily must achieve the fire-resistance rating required by IBC Table 601 for the construction type and by IBC Table 602 for the fire separation distance. UL Design U425 is the most widely referenced assembly series for CFS load-bearing exterior walls.

UL U425: 1-hour fire-resistance-rated load-bearing wall assembly. Typical tested configuration: 3-5/8 in. to 6 in. CFS studs, 20 gauge (33 mil) minimum, 16 in. o.c. spacing, with one layer of 5/8 in. Type X gypsum board (per ASTM C1396) on each face. Interior cavity insulation: 3-1/2 in. mineral wool friction-fit batts. This assembly achieves a 1-hour bearing-wall rating and STC 45-50 depending on insulation type. For 2-hour rating, the assembly requires two layers of 5/8 in. Type X gypsum board on each face with staggered joints and the same stud and insulation configuration.

UL U423 provides an alternative exterior wall configuration with enhanced resilient channel attachment for improved acoustic performance while maintaining the 1-hour fire-resistance rating. This assembly uses resilient channels at 24 in. o.c. on one side with a single layer of 5/8 in. Type X gypsum, achieving STC 52-56.

Key Benefits:

• UL U425 series covers the most common mid-rise CFS exterior wall conditions with a single tested assembly family
• Continuous insulation (CI) can be added outboard of the gypsum sheathing without affecting the fire rating — enabling energy code compliance without assembly re-testing
• 20-gauge studs at 16 in. o.c. provide adequate axial capacity for 5-story load-bearing conditions per AISI S240 and AISI S100 effective width method

4.2 Interior Load-Bearing Walls (Corridor and Demising)

Interior load-bearing walls in multifamily mid-rise include corridor walls and demising (party) walls between dwelling units. IBC Section 708 requires dwelling unit separation walls to provide a minimum 1-hour fire-resistance rating (or 1/2-hour in fully sprinklered Type IIB buildings). Most multifamily developers specify 1-hour minimum for all unit-to-unit and unit-to-corridor walls regardless of construction type, as this provides both fire safety and acoustic separation.

UL U419: 1-hour fire-resistance-rated load-bearing CFS partition. Typical configuration: 3-5/8 in. CFS studs, 20 gauge minimum, 24 in. o.c. spacing, one layer 5/8 in. Type X gypsum board on each side, 3-1/2 in. glass fiber insulation in the cavity. This assembly achieves STC 45-48. For enhanced acoustic performance at corridor walls, adding resilient channels on one side (per UL U423 modifications) increases the STC to 52-56, which meets the IBC Section 1207 requirement for STC 50 at dwelling unit separations.

For 2-hour rated corridor walls (required where corridor serves as exit access in some jurisdictions), UL U411 provides a tested configuration with two layers of 5/8 in. Type X gypsum board on each side of 3-5/8 in. CFS studs at 16 in. o.c., achieving 2-hour bearing and STC 55-58.

4.3 Area Separation Walls

Area separation fire walls per IBC Section 706 enable larger building footprints by dividing a structure into separate building areas per IBC Table 506. For Group R-2 occupancies, fire walls require a minimum 2-hour fire-resistance rating. These walls must maintain structural stability under fire conditions such that collapse of construction on one side does not cause collapse of the wall or construction on the opposite side.

CFS double-stud area separation walls achieve 2-hour and 3-hour ratings using independent stud rows separated by an air gap. The typical 2-hour configuration per UL U466: two independent rows of 3-5/8 in. CFS studs at 24 in. o.c. with a 1 in. minimum air gap between rows. Each side receives two layers of 5/8 in. Type X gypsum board. Mineral wool insulation fills both cavities. This assembly achieves a 2-hour fire-resistance rating and STC 60+, exceeding the IBC Section 1207 minimum of STC 50 for dwelling unit separation by a significant margin.

For 3-hour rated area separation walls, the configuration adds a third layer of 5/8 in. Type X gypsum board on each face of the double-stud assembly, or increases stud gauge to 16 gauge with enhanced fastening per the specific UL listing. The 3-hour rating is required for fire walls in Type I construction but is sometimes specified voluntarily in Type II CFS buildings for insurance underwriting benefits.

Key Benefits:

• Double-stud CFS area separation walls achieve STC 60+ — significantly exceeding code minimum acoustic requirements
• Independent stud rows provide structural independence per IBC Section 706.2 collapse criteria
• CFS area separation walls weigh 8-12 psf compared to 55-75 psf for 8 in. CMU — reducing foundation loads by up to 85%
• Enables larger building footprints per IBC Table 506 area increase provisions

4.4 Shaft Walls

Elevator shafts, stairwell enclosures, and MEP (mechanical-electrical-plumbing) shaft enclosures require fire-resistance-rated construction per IBC Section 713. Shaft enclosures require a minimum 2-hour rating where connecting four or more stories, and 1-hour where connecting fewer than four stories.

CFS shaft wall assemblies use a C-runner (H-stud or I-stud) system that permits construction from one side — a significant labor advantage over conventional stud walls in shaft conditions where access from both sides is impractical. The typical CFS shaft wall assembly: 2-1/2 in. C-H studs at 24 in. o.c. with 1 in. gypsum liner panels inserted between the stud flanges, one layer of 5/8 in. Type X gypsum board on the exposed face, and 1 in. mineral wool in the cavity. This configuration achieves 1-hour rating. For 2-hour shaft walls, two layers of 5/8 in. Type X gypsum board are applied to the exposed face.

Integration with firestopping at shaft penetrations is critical. Every pipe, conduit, cable tray, and duct penetrating the shaft wall requires a tested firestop system per IBC Section 714. Shaft wall penetrations are among the most common code violations found during fire-rated assembly inspections — proper detailing in the construction documents is essential.

Key Benefits:

• One-sided installation — CFS shaft wall systems can be erected without access to the shaft interior
• Lighter than CMU shaft enclosures by 60-75%, reducing structural loads at elevator and stair cores
• 1-hour and 2-hour rated configurations using standard UL-listed components
• Accommodates differential movement better than rigid masonry shaft enclosures in mid-rise structures

5. CFS Floor-Ceiling Fire-Rated Assemblies

Floor-ceiling assemblies must achieve the fire-resistance rating required by IBC Table 601 and also meet the acoustic separation requirements of IBC Section 1207 (STC 50 / IIC 50 minimum between dwelling units). CFS joist floor-ceiling assemblies are documented in the UL L-series listings.

5.1 1-Hour and 2-Hour Floor-Ceiling Assemblies

UL L524: 1-hour fire-resistance-rated floor-ceiling assembly. Typical tested configuration: 8 in. to 12 in. CFS C-joists, 18 gauge (43 mil) minimum, 16 in. o.c., with 3/4 in. plywood or OSB subfloor, 1-1/2 in. lightweight concrete topping (or approved gypsum-concrete), and one layer of 5/8 in. Type X gypsum ceiling board attached to resilient channels at 24 in. o.c. The assembly achieves a 1-hour rating with STC 52-55 and IIC 52-55, meeting IBC Section 1207 acoustic requirements.

UL L547: 2-hour fire-resistance-rated floor-ceiling assembly for CFS joist construction. This assembly adds a second layer of 5/8 in. Type X gypsum ceiling board with staggered joints and increases the concrete topping thickness to 1-1/2 in. minimum. CFS joists must be 16 gauge (54 mil) minimum at 16 in. o.c. The assembly achieves STC 55-60 and IIC 55-58.

5.2 Sound Transmission Considerations

Fire and acoustic performance must be evaluated together — a floor-ceiling assembly that achieves the fire rating but fails the STC 50 / IIC 50 requirements of IBC Section 1207 is still non-compliant. The critical variables for acoustic performance in CFS floor-ceiling assemblies are: concrete or gypsum-concrete topping weight (mass law), resilient channel isolation (vibration decoupling), cavity insulation density, and ceiling gypsum board mass. Assemblies without concrete topping (such as UL L514) typically require additional acoustic treatments to meet IIC 50.

5.3 The Non-Combustible Advantage for Floor Systems

CFS floor-ceiling assemblies offer a decisive advantage over wood joist assemblies: the structural members do not burn. In a fire exposure from below, the gypsum ceiling membrane protects the CFS joists from heat. If the membrane fails, CFS joists lose strength gradually as steel temperatures rise — but they do not ignite and contribute to fire growth. Wood joists, by contrast, ignite and contribute fuel to the fire once the ceiling membrane fails, accelerating structural collapse. Fire loss data consistently shows that non-combustible structural systems have lower total fire damage costs compared to combustible systems of identical fire-resistance rating.

Key Benefits:

• Dual fire and acoustic compliance from UL-listed CFS floor-ceiling assemblies — STC 50+ and IIC 50+ achievable with standard configurations
• Non-combustible joists eliminate structural fuel contribution during fire events
• Concrete topping provides mass for both fire resistance and impact sound insulation (IIC)
• Resilient channel ceiling attachment is standard in all rated CFS floor assemblies — acoustic isolation is built into the fire-rated system

6. Firestopping and Penetration Management

A fire-rated assembly is only as effective as its weakest penetration. IBC Section 714 requires that all penetrations through fire-rated assemblies be protected by through-penetration firestop systems tested per ASTM E814 (Standard Test Method for Through-Penetration Firestops). The firestop system must maintain the fire-resistance rating of the assembly being penetrated.

6.1 UL Firestop Systems for CFS Assemblies

UL publishes system-specific firestop listings (CAJ, CW, and WL series) that are tested with specific wall and floor assembly types. When specifying firestopping through a CFS fire-rated assembly, the firestop system must be listed for use with that assembly type — a firestop system tested with a CMU wall cannot be used in a CFS gypsum wall assembly without a specific listing.

Common penetration types requiring firestopping in multifamily CFS construction include: electrical conduit (metallic and non-metallic), copper and CPVC plumbing, PVC drain-waste-vent piping, HVAC sheet metal duct, cable trays and data cabling, and fire sprinkler piping. Each penetrant type requires a specific UL-listed firestop system — there is no universal firestop product that covers all conditions.

6.2 Head-of-Wall Joints

The joint between the top of a fire-rated CFS wall and the underside of the floor or roof assembly above (head-of-wall joint) requires a fire-rated joint system per IBC Section 715. CFS walls are typically designed with a deflection track at the top that accommodates live-load deflection and story drift — this gap must be protected with a UL-listed joint system that accommodates the specified movement while maintaining the fire rating. Typical head-of-wall joint systems use mineral wool safing insulation with intumescent sealant or fire caulk.

Key Benefits of CFS Firestopping vs. Wood:

• Non-combustible framing eliminates annular space fire spread around penetrants — steel studs do not char or burn away from firestop materials
• CFS stud cavities accept standard UL-listed firestop systems without modification for combustible substrates
• Metallic CFS framing maintains dimensional stability at elevated temperatures longer than wood, preserving firestop integrity
• Head-of-wall joint systems integrate with CFS deflection track design — movement accommodation is engineered into the wall system

7. Massachusetts-Specific Considerations

Massachusetts adopts the IBC through the 780 CMR (Massachusetts State Building Code). The current 780 CMR 9th Edition is based on IBC 2021 with Massachusetts-specific amendments that affect fire-rated assembly design in CFS multifamily construction.

780 CMR includes amendments to IBC Chapter 7 (Fire and Smoke Protection Features) that may impose additional requirements beyond the base IBC. Specifically, Massachusetts fire marshals have historically enforced stricter interpretations of fire wall requirements in multifamily residential projects, particularly regarding area separation walls in mixed-use buildings with ground-floor commercial and upper-floor residential occupancies. Designers should coordinate with the local AHJ early in the design process to confirm fire wall requirements for the specific project.

The Massachusetts Stretch Energy Code (225 CMR 22.00) and the Specialized Opt-in Code impact fire-rated wall assembly design through continuous insulation requirements. Exterior wall assemblies must now achieve higher effective R-values — typically requiring R-10 to R-15 continuous insulation outboard of the sheathing. This continuous insulation is applied outboard of the fire-rated gypsum sheathing and does not affect the fire-resistance rating of the base UL assembly, provided the CI material is non-combustible mineral wool or meets the NFPA 285 assembly fire test requirements for foam plastic insulation. Specifiers must verify that the CI material and attachment method are compatible with the UL-listed fire-rated wall assembly.

Regional considerations for New England CFS projects also include stricter energy code compliance documentation, enhanced commissioning requirements that may require fire-rated assembly inspection as part of the building envelope commissioning scope, and potential 780 CMR amendments affecting height and area limitations for CFS buildings. Always verify the current edition of 780 CMR and any local amendments before finalizing fire-rated assembly specifications for Massachusetts projects.

Key Benefits:

• 780 CMR 9th Edition aligns with IBC 2021 — UL assemblies listed per IBC 2021 are directly applicable
• CFS non-combustible framing simplifies NFPA 285 compliance for exterior walls with foam plastic CI
• CI layer is outboard of the fire-rated sheathing — energy code compliance does not require re-testing the fire-rated assembly

8. Specifying CFS Fire-Rated Assemblies: Best Practices

Proper specification of CFS fire-rated assemblies in construction documents is essential for code compliance, plan review approval, and field quality assurance. Ambiguous or incomplete specifications are the leading cause of fire-rated assembly deficiencies identified during construction inspections.

8.1 Reference Standards to Include

Every CFS fire-rated assembly specification should reference the following standards: AISI S240 (North American Standard for Cold-Formed Steel Structural Framing) for structural design and installation requirements, the UL Fire Resistance Directory for the specific assembly listing, ASTM E119 or UL 263 for fire test standard, ASTM C1396 for gypsum board material standard, and ASTM E814 for through-penetration firestop test standard. The specification should also reference AISI S100 (North American Specification for the Design of Cold-Formed Steel Structural Members) for structural member design.

8.2 Specification Best Practices

Specify fire-rated assemblies by UL Design Number with all tested components listed. Do not specify fire-rated assemblies by generic performance criteria alone (e.g., "provide 1-hour rated wall") — always include the UL Design Number as the basis of design. Include a substitution clause requiring any proposed alternative assembly to be UL-listed with an equivalent or better fire-resistance rating, tested per ASTM E119, with documentation submitted to the architect for review prior to installation.

Coordinate fire-rated wall assemblies with the structural engineer to confirm that the stud size, gauge, and spacing specified in the UL listing are compatible with the structural design loads calculated per AISI S100 effective width method and ASCE 7 load combinations. In many cases, the structural engineer will require heavier gauge studs or closer spacing than the minimum required by the UL listing — the fire-rated assembly must accommodate the actual structural members without voiding the listing.

8.3 Quality Assurance & Field Inspection

Require special inspection of fire-rated assemblies per IBC Section 1705. Special inspection should verify: correct stud size, gauge, and spacing; correct gypsum board type (Type X vs. Type C), thickness, and number of layers; correct fastener type, size, and spacing; correct insulation type and installation; and correct firestop installation at all penetrations. Document the UL Design Number on the construction drawings at every fire-rated assembly — field inspectors must be able to verify installed conditions against a specific tested listing.

8.4 Common Specification Mistakes to Avoid

• Specifying a non-bearing UL assembly for a load-bearing wall condition
• Omitting the UL Design Number and specifying only a generic performance requirement
• Failing to coordinate stud gauge between structural and fire-rated assembly requirements
• Neglecting to specify firestop systems for penetrations through rated assemblies
• Using Type C gypsum board where the UL listing specifies Type X, or vice versa
• Omitting head-of-wall joint fire-rated joint system details at deflection tracks
• Failing to specify resilient channel requirements when acoustic performance (STC) is also required

9. Conclusion

Cold-formed steel framing provides a comprehensive, code-compliant fire resistance solution for mid-rise multifamily construction — from 1-hour bearing walls to 3-hour area separation fire walls, from 1-hour floor-ceiling assemblies to 2-hour shaft enclosures. The UL Fire Resistance Directory contains tested assemblies for every fire-rated condition encountered in multifamily design. CFS achieves these ratings with non-combustible framing that contributes zero fire fuel load, at weights 60-85% less than concrete or masonry alternatives, with faster installation and lower total installed cost.

At AAC Steel, we engineer and fabricate cold-formed steel framing systems with the precision and documentation that architects and specifiers require — including fire-rated assembly compliance verification for every project. Our engineering team reviews UL assembly requirements against structural design loads to ensure that fire-rated specifications are fully coordinated with the structural framing design per AISI S100 and AISI S240.

Contact AAC Steel for fire-rated assembly consultation on your next multifamily mid-rise project. Our team provides UL assembly selection support, fire-rated wall and floor detail development, and firestopping coordination — from design through fabrication.

Note: UL Design Numbers and assembly configurations referenced in this guide are current as of IBC 2021. Verify current listings in the UL Fire Resistance Directory (https://productspec.ul.com/en/fire) for the latest tested assemblies. Local jurisdictions may have additional requirements. Code references are based on IBC 2021; IBC 2024 adoption may introduce changes — verify applicable code edition with the authority having jurisdiction.