Cold formed steel is steel that has been shaped into structural components at room temperature, rather than being heated and molded while red-hot. Flat sheets of steel are fed through rollers or pressed into shapes like C-channels, angles, and tracks without any heat applied. This process changes the steel’s properties, making it stronger but less flexible than the original material. It’s widely used in building construction for wall framing, floor joists, and roof trusses as a lightweight, non-combustible alternative to wood.
How Cold Formed Steel Is Made
The process starts with flat steel coils, typically made from steel that has already been rolled thin at a steel mill. These flat sheets are fed into a roll forming machine, which is essentially a series of paired rollers that progressively bend the steel into the desired cross-section. Each set of rollers makes a slightly more aggressive bend than the last, gradually shaping a flat strip into a finished profile like a C-shape or a Z-shape.
If the design calls for holes, notches, or slots, the steel passes through a punching station before the rollers do their work. At the end of the line, a cut-off die shears the continuous shape to the correct length. The alternative method, press braking, uses a single powerful press to bend a pre-cut sheet along a straight line. Roll forming works best for high-volume production of consistent shapes, while press braking suits smaller runs or custom angles.
The key distinction from hot rolled steel is temperature. Hot rolling happens above 1,700°F, where steel is soft and easy to shape. Cold forming happens at or slightly above room temperature, which requires more force but produces a fundamentally different product.
What Cold Forming Does to the Steel
Bending steel at room temperature causes something called strain hardening. The steel’s internal grain structure gets compressed and rearranged at the bend points, which increases yield strength (the force needed to permanently deform it) but reduces ductility (how much it can flex before cracking). At the corners of a cold formed section, ductility can drop by 20% to 90% compared to the original flat sheet. This tradeoff is central to how engineers design with the material.
Overall, cold formed steel can be up to 20% stronger than equivalent hot rolled steel. That added strength comes with a catch: higher internal stresses locked into the material. Hot rolled steel cools gradually and essentially relaxes into a stress-free state. Cold formed steel retains tension from the forming process, which can cause warping if the material is cut or welded without accounting for those stresses.
Cold Formed vs. Hot Rolled Steel
The practical differences between the two come down to three things: surface quality, dimensional precision, and strength.
- Surface finish: Hot rolled steel has a rough, scaly surface that often needs cleaning or treatment before use. Cold formed steel has a smooth, shiny surface free of rust and scale, which is ready for coating or finishing right off the line.
- Dimensional tolerances: Hot rolled steel shrinks as it cools, making final dimensions somewhat unpredictable. Cold formed steel doesn’t shrink after forming, so parts come out highly precise with little to no secondary processing needed.
- Strength and weight: Cold formed sections achieve favorable strength-to-weight ratios, meaning thinner, lighter pieces can carry substantial loads. Hot rolled steel is better suited for massive structural elements like I-beams and columns where raw bulk matters more than precision.
Hot rolled steel costs less per pound and works well for applications where tight tolerances aren’t critical, like railroad tracks or structural beams. Cold formed steel costs more to produce but saves labor downstream because the parts arrive closer to their final form.
Common Gauges and Thicknesses
Cold formed steel thickness is specified by gauge number, where a higher gauge means thinner steel. The range used in construction typically falls between 12 gauge and 33 gauge. Here’s what that translates to in actual thickness:
- 12 gauge: 0.109 inches (about 2.8 mm), used for heavy structural members
- 14 gauge: 0.078 inches (about 2.0 mm)
- 18 gauge: 0.050 inches (about 1.3 mm), common for load-bearing wall studs
- 20 gauge: 0.0375 inches (about 1.0 mm), typical for non-load-bearing framing
- 25 gauge: 0.022 inches (about 0.6 mm), used for lighter applications
- 33 gauge: 0.009 inches (about 0.2 mm), among the thinnest structural gauges
The gauge system can be counterintuitive. Engineers and specification documents often use “mils” (thousandths of an inch) instead, referring to a 20-gauge stud as “33 mil” or an 18-gauge stud as “43 mil” to avoid confusion.
Where It’s Used in Construction
The most visible application is light-gauge steel framing, where cold formed C-shaped studs and tracks replace wood 2x4s and 2x6s in walls. These studs look like the metal framing you’d see in a commercial building’s interior walls, but they’re increasingly common in residential construction too. The C-shape provides stiffness while keeping the member lightweight.
Floor joists are another major use. Cold formed steel joists have become popular where non-combustible material and long unsupported spans are required. A steel joist can span greater distances than an equivalent wood joist without intermediate support, which opens up floor plans. Roof trusses, headers above doors and windows, and curtain wall framing round out the typical structural applications.
Beyond building frames, cold formed steel shows up in metal roofing panels, steel decking for concrete floors, storage racks, and guardrails. The roll forming process is well suited to any product that needs a consistent cross-section in long lengths.
Corrosion Protection
Steel rusts, so cold formed members are almost always coated before they leave the factory. The standard protection is a zinc coating applied through continuous sheet galvanizing, where the steel passes through a bath of molten zinc at high speed. The coating designations you’ll see on spec sheets, like G60 and G90, refer to the total weight of zinc on both sides of the sheet. G60 provides a coating about 0.51 mils thick, while G90 provides about 0.77 mils. G90 is the more common choice for structural framing exposed to moisture.
Other coating options include galvannealed (a zinc-iron alloy that paints well), zinc-aluminum alloys for enhanced corrosion resistance, and pure aluminum coatings for high-temperature applications. For most interior framing, G60 is sufficient. Exterior applications or humid environments like coastal buildings typically call for G90 or heavier coatings.
Fire Resistance
Steel itself doesn’t burn, which gives cold formed steel a baseline advantage over wood framing. But steel loses strength at high temperatures, so fire-rated assemblies rely on protective layers to keep the steel cool during a fire. The most common approach is gypsum wallboard: one or two layers of fire-resistant (Type X) gypsum board on each side of a steel stud wall can achieve 1-hour or 2-hour fire resistance ratings.
A typical 1-hour load-bearing wall uses 3.5-inch steel studs spaced 24 inches apart with a single layer of 5/8-inch Type X gypsum board on each side. Doubling the gypsum layers on each side bumps the rating to 2 hours. Fire-rated floor and ceiling assemblies combine steel joists with gypsum board below and concrete or lightweight concrete above. Depending on the configuration, cold formed steel assemblies can achieve fire ratings from 1 hour up to 4 hours for interior partitions and floor-ceiling systems.
Design Standards
In North America, cold formed steel design is governed by AISI S100, formally titled the North American Specification for the Design of Cold-Formed Steel Structural Members. The current edition is ANSI/SDI AISI S100-24. This standard covers how engineers calculate load capacity, account for the effects of cold working on material properties, and design connections between members. It applies in the United States, Canada, and Mexico, making it one of the more unified structural codes across the continent.
For prescriptive residential construction (where builders follow standardized tables rather than hiring an engineer for every wall), AISI S230 provides simplified rules for cold formed steel framing in houses up to certain sizes and load conditions.