Steel Cold Formed Steel Framing: Studs, Screws & Seismic Design

Blue-gray industrial tone—the interior of a low-rise framed building, silver C-shaped studs neatly standing on a bottom U-track, top track closing the wall, self-drilling screw heads visible at every stud-to-track intersection, a panel of OSB sheathing already fixed on one wall, diagonal steel strap bracing visible in the distance, natural light through window openings, no text.

Hot-rolled steel comes off a mill at roughly 1,000°C. Steel cold formed steel framing design starts at room temperature with coils 0.8–3.0 mm (12–25 gauge) thick, roll-formed into C-studs and U-tracks. It is light, precise, and screwed together—not welded. The structure lives or dies by the screw: its spacing, penetration, and edge distance. This CFS framing system is about three systems: C-stud/U-track wall framing, self-drilling screw connections, and seismic diaphragm action through structural sheathing.

This article treats the built system—studs, tracks, screws, and sheathing working together. Our steel thin walled member design piece covers effective width and post-buckling theory. A steel cold formed steel framing design article is about how the system is laid out and detailed, not how the member buckles.

CFS Framing vs Hot-Rolled vs Thin-Walled Theory

Hot-rolled structural steel uses plates 6 mm (1/4 in) and thicker, joined by welding or high-strength bolts, and carries heavy loads in factories, bridges, and tall buildings. Cold-formed steel (CFS) uses sheets 0.8–3.0 mm (12–25 gauge) thick, joined by self-drilling screws, and carries light-to-moderate loads in low-rise housing, commercial partitions, and roof trusses. The structural logic is different: hot-rolled frames rely on bare member strength; CFS frames rely on sheathing diaphragm action and the truss action of built-up stud panels.

The thin-walled member article (blog116) derives effective section width, post-buckling strength, and edge-stiffener theory. This article is the construction-system layer on top of that theory: how studs are spaced, which screws are specified, how straps brace the walls, and how sheathing converts the bare frame into a lateral-load-resisting system. The math belongs to blog116; the layout belongs here.

Typical applications are low-rise residential (1–3 stories), interior commercial partitions, roof purlins and trusses, and modular building cassettes. For the modular cassette parallel, see modular steel construction; for the broader light-vs-heavy framing choice, read light vs heavy steel.

Studs, Tracks & Joist Layout

The wall stud is a C-shaped section with a stiffened return lip at each flange edge. Standard depths run from C92 (3-5/8 in) for interior partitions to C200 (8 in) for exterior load-bearing walls, at gauges from 12 (2.7 mm) to 20 (0.9 mm). Studs are typically spaced 400 or 600 mm (16 or 24 in) on center, with 600 mm spacing the residential default. Top and bottom U-tracks match the stud width; studs simply sit inside the track and are fastened at each end.

Floor joists and roof trusses use the same C-section family but deeper: C300 to C400 (12–16 in), spaced at 400 mm (16 in). Residential live loads run 1.9–2.5 kN/m² (40–50 psf); commercial floors can reach 3.5 kN/m² (75 psf). Roof trusses built from CFS chords and webs span 6–12 m (20–40 ft) and are usually shop-assembled with screws and shipped as truss bundles. For purlin and girt parallels, see steel purlin system; for residential context, read steel building homes.

Table 1: CFS Stud & Track Size Reference

Designation	Depth (mm / in)	Thickness (mm / gauge)	Typical Use	Spacing (mm / in)
C92	92 / 3-5/8	0.9–1.5 / 20–16	Interior partition	600 / 24
C150	150 / 6	1.2–2.0 / 18–14	Exterior load wall	400 / 16
C200	200 / 8	1.5–2.7 / 16–12	Exterior load wall, 2–3 story	400 / 16
C300 joist	300 / 12	1.5–2.4 / 16–13	Floor joist	400 / 16
C400 truss chord	400 / 16	2.0–2.7 / 14–12	Roof truss chord	Built-up

Track width matches stud depth; track gauge is typically one gauge lighter.

Self-Drilling Screw Connections

Every load path through these light-gauge steel studs ends at a screw. Self-drilling, self-tapping screws range from #6 to #14, with lengths from 13 to 75 mm (0.5 to 3 in). Wood-structure screws (sharp point, fine thread) fix sheathing to studs; metal-to-metal screws (self-drilling tip) join stud to track, joist to rim track, and strap to stud.

Shear strength per screw is modest. A typical #10 × 16 mm (5/8 in) screw carries 2.5–4.0 kN (560–900 lb) in shear per AISI S100, limited by tilt (the screw tilts in the thin sheets) and bearing (the steel sheet yields around the hole). Edge distance must be at least 10 mm (3/8 in) from the sheathing edge and 9.5 mm (3/8 in) from the stud flange edge to prevent tear-out. Screw spacing on sheathing edges is double the field spacing—this is the single most common field error.

For general connection design principles, see steel structure connection design; for comparison with bolted hot-rolled connections, read steel high strength bolt connection deep dive.

Table 2: CFS Self-Drilling Shear Connection Summary

Screw Size	Length (mm / in)	Shear Strength (kN / lb)	Edge Distance (mm / in)	Typical Use
#8 × 13	13 / 1/2	1.5–2.5 / 340–560	10 / 3/8	Gypsum board to stud
#10 × 16	16 / 5/8	2.5–4.0 / 560–900	10 / 3/8	OSB sheathing to stud
#10 × 25	25 / 1	3.0–4.5 / 675–1,010	12 / 1/2	Two C-members lapped
#12 × 32	32 / 1-1/4	4.0–6.0 / 900–1,350	12 / 1/2	Strap to stud
#14 × 50	50 / 2	6.0–9.0 / 1,350–2,020	15 / 5/8	Heavy moment strap

Values are indicative single-shear per AISI S100; verify against the manufacturer's ICC-ES report.

Designing a CFS Building Where Every Load Goes Through a Screw?

We size studs, spec self-drilling screws to AISI S100, and detail seismic strap bracing so the diaphragm holds in a quake. Tell us your building type, stories, and wind/seismic zone.

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Seismic Detailing & Diaphragm Action

The bare CFS frame is an open grid—it has almost no lateral stiffness. What turns it into a seismic system is the structural sheathing (OSB or gypsum board) screwed to the studs, which acts as a horizontal diaphragm. The diaphragm collects wind and seismic forces from the roof and floor and routes them to the vertical shear walls. Diaphragm stiffness depends on sheathing thickness, screw spacing, and panel layout—not on the bare studs.

At the shear walls, screw spacing tightens: 150 mm (6 in) on center at panel edges and around openings, 300 mm (12 in) on center in the field. Steel strapping (flat 30–50 mm wide strips) is installed diagonally between studs at walls that cannot be fully sheathed, and horizontal strap runs tie the wall top to the foundation. Anchor bolts through the bottom track into the concrete foundation complete the load path to the ground. Per AISI S400, these details are mandatory in seismic design categories C and above.

For broader seismic design principles, see steel building seismic design; for bracing system parallels in hot-rolled frames, read steel building bracing system; for a deep seismic design treatment, read steel structure seismic design deep dive.

Table 3: CFS Seismic Detailing Schedule

Element	Screw Spacing (mm / in)	Strap Type	Anchor Requirement	Notes
Shear wall panel edges	150 / 6 oc	—	Anchor bolts M12 @ 600 mm (24 in)	Highest demand
Shear wall field	300 / 12 oc	—	—	Standard OSB 11 mm (7/16 in)
Diagonal strap bay	300 / 12 oc	Flat 40 mm × 1.0 mm	End anchors M12	Unsheathed walls
Roof diaphragm	150 / 6 oc at edges	Continuous roof strap	—	Ties walls together
Foundation track	—	—	M12 @ 600 mm (24 in)	Minimum 75 mm (3 in) embedment

Schedule is indicative; final spacing follows AISI S400 and the project's seismic design category.

AISI S100 Provisions & Effective Width

AISI S100 is the North American Specification for Cold-Formed Steel. It provides two design methods. The Effective Width Method reduces the thin plate's width after local buckling, so the section properties are computed on the effective rather than full area. The Direct Strength Method uses the full section and computes the member's buckling load directly, avoiding iterative effective-width calculation.

Three buckling modes can occur: local buckling (the plate element buckles between stiffeners), distortional buckling (the lip-to-web corner rotates and deforms), and global flexural or torsional buckling (the whole stud bends or twists as a column). They can interact—local buckling triggers distortional buckling, which reduces the global strength—and all three must be checked. A practical steel cold formed steel framing design sizes studs conservatively so none of these modes governs at service load. For the underlying member local stability theory, see steel member local stability. Per the AISI S100 North American Specification, these checks govern every CFS member.

Cost & Applications

A bare CFS stud-and-track system costs roughly $80–$150 per m² ($7.5–$14 per ft²) of floor area. Including sheathing, insulation, doors, and windows, a finished CFS building runs $200–$350 per m² ($19–$33 per ft²). The weight is roughly one quarter of a comparable masonry wall, which cuts foundation cost and speeds erection—members are pre-cut and screwed on site with hand tools.

CFS is right for low-rise residential (1–3 stories), hotel interior partitions, modular building cassettes, and roof purlins/trusses. It is not right for crane-runway buildings, long-span bridges, or high-rise structures, where hot-rolled or composite construction dominates. A cold-formed steel wall framing system stays economical only when the loads stay light and the stories stay low. For second-floor additions that use CFS over existing walls, see steel building expansion second floor; for modular cassette context, read modular steel construction.

Conclusion

A steel cold formed steel framing design is a system of C-studs, U-tracks, self-drilling screws, and sheathing acting as a diaphragm. Studs are selected by depth and gauge; screws are sized to AISI S100 shear tables; seismic behavior comes from screwed sheathing, strap bracing, and foundation anchors—not from the bare frame. CFS is not a miniaturized hot-rolled beam: it is a screwed, sheathed, diaphragm-driven system. Tell our engineers your building type, story count, and wind/seismic zone, and we will return with a stud layout and screw schedule.

Light Studs, Screws, and Sheathing—One CFS Frame That Works as a System.

We size C-studs, spec self-drilling screws to AISI S100, and detail seismic strap bracing so the diaphragm holds in a quake. Tell us your building type, stories, and wind/seismic zone.

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About the Author

Senior Structural Engineer

With over 20 years of hands-on experience in steel structure design and prefabricated building engineering, our in-house senior structural engineer has personally contributed to more than 500 steel building projects—including warehouses, industrial factories, aircraft hangars, agricultural buildings, and commercial structures. The focus is on translating design codes such as AISC 360, ASCE 7, and Eurocode 3 into buildable, cost-effective steel solutions that balance structural performance, fabrication efficiency, and total project cost.

Learn more about our engineering team

Case Example

A three-story residential build shows cold-formed steel working as a screwed, sheathed system. The building was about 1,950 m² (21,000 sq ft) of floor area, using C200 studs at 600 mm (24 in) spacing and CFS roof trusses spanning 9 m (30 ft), in a seismic category C region of an anonymized Oceania site. The critical risk was diaphragm shear, not bare stud strength. We specified 11 mm (7/16 in) OSB screwed at 150 mm (6 in) on panel edges and 300 mm (12 in) in the field, added diagonal flat-strap bracing, and anchored the bottom track at 600 mm (24 in). A six-person crew erected the frame in nine weeks; an on-load test showed deflection under L/240, and no screw pull-through was found on the punch list. The cassette parallel is in modular steel construction; the residential context is in steel building homes.

Frequently Asked Questions

Q1: What is cold-formed steel framing?

Cold-formed steel (CFS) framing uses thin steel sheets (0.8–3.0 mm / 12–25 gauge) roll-formed at room temperature into C-shaped studs and U-shaped tracks. Members are joined with self-drilling screws, not welds. It is the standard system for low-rise residential, commercial partitions, and roof trusses.

Q2: What stud sizes are standard for CFS walls?

Common wall studs range from C92 (3-5/8 in) for interior partitions to C200 (8 in) for exterior load-bearing walls, at gauges from 12 (2.7 mm) to 20 (0.9 mm). Studs are typically spaced 400 or 600 mm (16 or 24 in) on center.

Q3: How do self-drilling screws carry load in CFS?

Each screw resists shear by tilt and bearing in the thin steel sheets. A typical #10 × 16 mm screw has a shear strength of 2.5–4.0 kN (560–900 lb) per AISI S100. Edge distance must be at least 10 mm (3/8 in) to prevent tear-out.

Q4: Is CFS framing seismic-resistant?

Yes, when detailed correctly. Structural sheathing (OSB or gypsum) screwed to studs creates a horizontal diaphragm that transfers wind and seismic loads to shear walls. Shear walls use screw spacing at 150 mm (6 in) at edges and 300 mm (12 in) in the field, plus steel strap bracing and foundation anchor bolts per AISI S400.

Q5: Can CFS be used for multi-story buildings?

Yes, but practically only up to 3–5 stories depending on wind and seismic zone. Beyond that, member slenderness, screw connection limits, and diaphragm stiffness make CFS uneconomical compared with hot-rolled steel or concrete frames. Each additional story requires deeper studs, heavier gauges, and more shear walls.

Reference Links

• AISI S100 — North American Specification for Cold-Formed Steel — design standard for CFS members, screw connections, and effective width.
• ASCE 7 — Minimum Design Loads and Associated Criteria for Buildings — wind and seismic load inputs for CFS diaphragm and shear wall design.