Technical Specifications

Cold-Formed Steel Framing Details: IBC Construction Types, Load-Bearing Applications, and BIM Coordination

Cold-formed steel (CFS) load-bearing framing qualifies for IBC Types I, II, and III construction because it is non-combustible under ASTM E136. Type IIB is the standard for 5–6 story multifamily, requiring no fire-resistive coating on structural members, while panelized CFS fabricated to ±1/16″ tolerance eliminates the RFIs and dimensional drift common in field-built framing.
  • 8-minute read
Who this article is for: Architects at design development, structural engineers beginning CFS design, and GC project managers evaluating panelized CFS.

Technical reference for specifying CFS framing in mid-rise multifamily, covering IBC construction types, load-bearing details, and BIM coordination best practices.

IBC Construction Types for CFS Load-Bearing Framing

Under IBC 2021 Section 602, a structural frame must be non-combustible to qualify for Types I, II, or III construction. CFS satisfies this requirement directly — no encasement, no intumescent coating, no additional protection required to establish non-combustibility. The steel itself is the non-combustible material.

Construction Type Structural Frame Fire-Resistance Rating CFS Qualification Max Height (R-2 Sprinklered)
Type IA 3-hour CFS + SFRM (3-hr listed assembly) Unlimited
Type IB 2-hour CFS + SFRM (2-hr listed assembly) Unlimited
Type IIA 1-hour CFS + SFRM (1-hr listed assembly) 85 ft
Type IIB 0-hour (no rating required) CFS non-combustible — no SFRM needed 75 ft (55 ft unsprinklered)
Type IIIA 1-hour CFS framing with combustible exterior elements permitted 85 ft

Type IIB is the most widely used construction type for CFS mid-rise multifamily in New England because it offers the maximum practical height for residential use (75 feet, sufficient for 5–6 stories at standard floor-to-floor heights) with the minimum fire protection burden: no SFRM on structural members is required. Type IIA achieves the same height limit but requires spray-applied fire-resistive material on every CFS member, adding cost and complicating inspection sequencing.

Standard CFS Section Properties for Load-Bearing Multifamily

CFS structural members are designated by a standardized naming convention: depth × type × flange width – thickness. For example, 600S162-54 designates a 6-inch depth (600), S-stud profile (S), 1-5/8-inch flange (162), at 54 mil thickness (54 mil = 16 ga). All section properties are published in the AISI Cold-Formed Steel Design Manual; design is per AISI S100-16.

Section Depth Thickness (mil / ga) Common Application
362S162-33 3-5/8″ 33 mil (20 ga) Non-load-bearing partitions, interior walls
362S162-43 3-5/8″ 43 mil (18 ga) Light load-bearing applications, 1–2 story
600S162-54 6″ 54 mil (16 ga) Mid-rise load-bearing walls, 3–5 story
600S162-68 6″ 68 mil (14 ga) Heavy load-bearing, 5–7 story
800S162-54 8″ 54 mil (16 ga) Deep section for thermal CI + load-bearing; MA Stretch Code wall assemblies
800S162-68 8″ 68 mil (14 ga) High-load mid-rise, 6–8 story

CFS stud selection for load-bearing multifamily walls is governed by the combined axial plus bending check under AISI S100-16 Section H. Deeper studs (600S vs. 362S) increase the moment of inertia and section modulus, improving both axial capacity and lateral bending resistance. Heavier gauges (68 mil vs. 54 mil) increase the area and wall thickness, directly increasing axial capacity. For a typical 5-story New England multifamily project, first-floor load-bearing walls with 9-foot stud heights and tributary floor loads of 12–18 kips per lineal foot typically require 600S162-68 or 800S162-68 studs at 12 or 16 inches on center.

Panelized CFS vs. Field-Built CFS and BIM Coordination

Factor Panelized CFS (AAC Steel) Field-Built CFS Wood Stick Framing
Dimensional tolerance ±1/16″ ±3/8″ ±3/8″ (plus wood shrinkage 0.5–2%)
BIM coordination Direct from model to CNC fabrication file; clashes resolved before steel is cut Drawing-based; clashes discovered at installation Drawing-based; clashes discovered at installation
Schedule above 4 stories 20–55% faster than wood stick framing; 15–30% faster than field-built CFS Baseline for CFS Baseline for wood
RFIs per building (framing-related) Typically <5 per building 15–40+ per building 20–50+ per building

At 5 stories, dimensional tolerance errors compound. A ±3/8-inch error at the first floor becomes an out-of-plumb condition that accumulates floor by floor — by the fifth floor, compounding errors can exceed 1 inch of cumulative offset. CNC-fabricated panels at ±1/16-inch tolerance hold dimension precisely across all five floors, eliminating cumulative drift.

The panelized CFS BIM workflow proceeds through seven stages: model input from the architect/structural engineer, shop drawing development, clash detection against the MEP and architectural model, clash resolution before fabrication begins, CNC fabrication file generation, panel labeling and sequencing by installation order, and just-in-time site delivery 2–3 weeks after slab work begins. On properly coordinated projects, framing-related RFIs stay under 5 per building — a fraction of the 15–40+ typical on field-built or wood-framed projects of comparable size.

Head-of-Wall and Floor Connection Details

The head-of-wall condition — where the top of the CFS load-bearing wall meets the floor system above — uses one of two configurations:

  • Slip track (deflection head): Stud tops slide inside the top track, allowing the floor above to deflect without transferring bending moment into the stud. Deflection allowance is typically L/240 to L/360 of the stud height depending on the wall finish system.
  • Fixed track: Stud tops are fastened to the top track, creating a semi-fixed connection that transfers shear from the floor to the wall. Less common than slip tracks for interior load-bearing walls in mid-rise CFS.

Floor-to-floor connections are designed per AISI S240-20 in two standard configurations: ledger angle connection, where a CFS angle is attached to wall studs to support floor joists from the interior side, and track-to-track connection, where the bottom track of the upper-floor panel bears directly on the top track of the lower-floor panel with bearing stiffeners at each stud to prevent local buckling.

Multi-story CFS load-bearing walls require continuous holdown rod assemblies to transfer uplift forces through the full building height to the foundation: threaded rod running from the foundation anchor bolt through each floor to shear wall end posts (chord studs), bearing plate and nut at each floor level, coupler nuts connecting rod segments, and chord studs designed per AISI S240-20 Table B2.2 to resist both compressive gravity load and tensile holdown force.

Installation Sequence and Framing Schedule

Panelized CFS installation follows eight steps: foundation/slab pour with anchor bolts set per structural drawings; first floor panel delivery 2–3 weeks after slab work begins; panel installation via crane, plumbed and anchored to the slab; floor system installation above the walls; repeat floor by floor at 5–7 working days per floor; MEP rough-in through pre-punched web openings; framing inspection per IBC Chapter 17 before concealment; and fire-rated gypsum board assemblies applied per the UL sequence.

For mid-rise multifamily above 4 stories, panelized CFS is the fastest structural framing method available. The 20–55% schedule advantage over wood stick framing comes from three compounding sources: concurrent fabrication (panels are ready by the time the slab cures), install-only labor (no field cutting or measuring), and sequenced delivery (panels arrive labeled in installation order).

On a typical 5-story mid-rise multifamily building: first floor framing begins day 1 after slab cure, each floor takes 5–7 working days, and total above-grade framing runs approximately 4–6 weeks. The wood stick framing equivalent is 8–12 weeks, plus another 8–12 weeks for the podium if Type IIIA is used.

Frequently Asked Questions

What IBC construction types allow cold-formed steel load-bearing framing?

CFS qualifies for Types I, II, and III construction under IBC 2021 because it is non-combustible per ASTM E136. Type IIB is the standard for 5–6 story multifamily — no SFRM required on structural members. Type IIA, IB, and IA require SFRM on structural members for the 1-, 2-, and 3-hour ratings respectively.

What is the standard stud section for 5-story CFS load-bearing walls?

Typical first-floor load-bearing walls in 5-story New England multifamily use 600S162-68 or 800S162-68 studs at 12 or 16 inches on center, with 9-foot stud heights and tributary floor loads of 12–18 kips per lineal foot. Final selection is per AISI S100-16 Section H combined axial plus bending check by the structural engineer of record.

What is the difference between panelized CFS and field-built CFS?

Panelized CFS is fabricated off-site on CNC HOWICK equipment to ±1/16″ tolerance, delivered labeled and sequenced by installation order. Field-built CFS is fabricated on site at ±3/8″ tolerance. Panelized CFS is 15–30% faster to install and generates fewer RFIs (typically <5 vs. 15–40+).

How does BIM coordination work for panelized CFS delivery?

The workflow proceeds through seven stages: model input from the architect/structural engineer, shop drawing development, clash detection against MEP and architectural models, clash resolution, CNC fabrication file generation, panel labeling and sequencing, and just-in-time site delivery. All clashes are resolved at the BIM stage before any steel is cut.

References

  • International Code Council — IBC 2021: International Building Code, Section 602, Chapter 17.
  • American Iron and Steel Institute — AISI S100-16: North American Specification for the Design of Cold-Formed Steel Structural Members.
  • American Iron and Steel Institute — AISI S240-20: North American Standard for Cold-Formed Steel Structural Framing.
  • ASTM International — ASTM E136-22: Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750°C.
  • HOWICK Ltd — CNC roll-forming equipment specifications and tolerances.
  • Steel Framing Industry Association (SFIA) — Cold-Formed Steel Framing Design Guide.
  • Board of Building Regulations and Standards — 780 CMR: Massachusetts State Building Code, 9th Edition.

Ready to Coordinate Panelized CFS for Your Project?

To discuss CFS framing specification, BIM coordination, or panel fabrication for your mid-rise multifamily project, contact our engineering team at nick@aacsteel.com or 617-560-0349.

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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