12.2 Metals & Metal Framing

Light-Gauge Steel Framing

Light-gauge steel framing (cold-formed steel) is formed from sheet steel into studs, tracks, and joists by roll-forming galvanized steel into C-shapes (studs) and U-shapes (tracks). Studs are designated by web depth, flange width, return lip, and steel thickness (gauge). Common stud sizes match wood dimensions: 3-5/8 inches (equivalent to a 2x4), 6 inches (equivalent to a 2x6), and 8 inches or deeper for taller walls or heavier loads. Commercial cold-formed steel framing is governed by 2018 IBC Chapter 22, which references AISI (American Iron and Steel Institute) standards.

Quick Answer: Light-gauge steel studs are sized by web depth (3-5/8, 6, 8 inches) and gauge (thickness); tracks are U-shaped sections that receive the stud flanges at top and bottom.

Stud Gauges and Thickness

Steel thickness is specified by gauge (in mils): lower gauge numbers mean thicker steel. 20-gauge (33 mil) is the thinnest structural commonly used; 16-gauge (54 mil) and 14-gauge (68 mil) are used for load-bearing and tall-wall conditions. 25-gauge (18 mil) and 22-gauge (27 mil) studs are non-load-bearing partition material only.

Steel Framing vs Wood

Steel framing is straight, dimensionally stable, inorganic (no rot, no termites), and lighter than comparable wood. It does not swell or shrink with moisture, so drywall seams are more stable. Steel studs will not warp, split, or cup, and they are unaffected by Arizona's dry climate or subterranean termites, which are a significant advantage in the desert Southwest. Disadvantages include thermal conductivity (steel conducts heat far more efficiently than wood, creating thermal bridging that must be broken with insulation or foam at stud-to-sheathing interfaces), susceptibility to corrosion if the galvanizing is compromised, and the need for specialized tools (aviation snips, screw guns, self-tapping screws). Steel framing also requires attention to sound transmission: steel studs transmit vibration more readily than wood, so acoustically rated assemblies often use resilient channel or isolated hat channel.

Web depth is the primary dimension: a 3-5/8-inch stud is roughly equivalent to a 2x4, a 6-inch stud to a 2x6. Flange width typically ranges from 1-1/4 to 1-5/8 inches. The return lip (the turned-back edge on a C-shape stud) stiffens the section and prevents rotation. Studs are punched at the factory with knockouts for utilities, typically at 24-inch intervals along the web.

Fastening Steel Framing

Steel studs are fastened with self-drilling, self-tapping screws (#6, #7, or #8 pan-head or bugle-head) driven by a screw gun. Studs-to-track connections use one screw per flange at each end (minimum two screws per connection). Structural connections may require more screws per the manufacturer's published load tables. Welding is used for heavier structural steel, not light-gauge framing. Pneumatic pins are an alternative on some products.

Screw selection depends on the total thickness of steel being joined: a #6 self-drilling screw typically drills up to 0.030 inch of steel, a #8 up to 0.060 inch. For thicker combinations (back-to-back studs or heavy headers), a screw with a longer drill point is required. Pan-head screws are used for track-to-stud connections; bugle-head screws for attaching drywall to steel studs because the head seats flush into the paper without tearing it. Overdriving screws into light-gauge steel can strip the hole or spin the stud; screw guns with depth-sensitive clutches prevent overdriving.

Load-Bearing vs Non-Load-Bearing

Load-bearing studs carry gravity loads from roofs and floors above and must be sized by span, height, and load per AISI standards referenced by 2018 IBC Chapter 22, or the 2018 IRC prescriptive tables for cold-formed steel in residential construction. Non-load-bearing (partition) studs carry only their own weight and lateral loads from finishes; 25-gauge studs at 24 inches o.c. are typical for interior partitions.

Corrosion Protection

Steel framing components are galvanized with a zinc coating. G90 (0.90 oz/sf minimum zinc) is the standard coating for interior framing per ASTM International (ASTM) A653. Heavier coatings or ASTM A653 SQ grade apply to exterior or high-humidity conditions. Cut ends expose bare steel and should be located where protected from moisture or treated with cold galvanizing compound. Steel must not contact dissimilar metals (copper, brass) in wet conditions; galvanic corrosion degrades the zinc layer.

Basic Structural Steel Concepts

Structural steel for commercial work uses wide-flange (W-shape) beams designated by nominal depth and weight per foot, for example W12x26 equals a 12-inch nominal depth at 26 lb/ft. Columns are typically W-shapes, HSS (Hollow Structural Sections), or pipe. Connections use high-strength bolts (A325 or A490, bearing or slip-critical) or shop welding per the American Welding Society (AWS) D1.1. Field bolting is preferred for erection speed. Bearing plates distribute column loads to concrete or masonry. Structural steel fabrication and erection follow AISC (American Institute of Steel Construction) 360 specifications, referenced by 2018 IBC Chapter 22.

Connection types are classified as bearing (bolts resist shear by bearing against the connected material) or slip-critical (bolts are tensioned to a specified minimum so friction between plies resists the load). Slip-critical connections are used where load reversal or vibration is expected, or where the connection is subject to fatigue. Shop welding is typically performed under controlled conditions; field welding requires a certified welder and weather protection. All structural steel connections must be detailed on shop drawings reviewed and stamped by the engineer of record before fabrication.

Quick Answer: Wide-flange beams are designated by depth and weight (W12x26 equals 12-inch depth at 26 lb/ft); connections use A325 or A490 high-strength bolts or AWS D1.1 welding.

On the B-1/B-2 commercial general building trade exam, Metals carries 13 of 100 items — the heaviest trade domain tested.