Cold Formed Steel Framing Grows Up
Specialized, innovative elements eliminate the expense and hassles of built-up pieces.
Cold formed steel framing began as a kind of alternative lumber but it is has finally come into its own. Basic steel studs and track no longer need to be cut and combined to create more complex shapes for headers and other special framing conditions. Standardized, code-approved, pre-fabricated elements solve challenges quickly, consistently and reliably. They speed up construction and streamline inspections, saving time and headaches. These standardized components also improve job site safety through less cutting and welding.
The CFSF system is founded on studs (vertical members usually formed in a C-shaped cross-section) and track (U-shaped horizontal framing members). Track is sized to accommodate the overall width of studs. Conventional studs and track are generally adequate for a simple wall with no rough openings.
If there is a rough opening in the wall—a door, window, or large HVAC duct, for example—the header of the RO must be strong enough to bear the load of the cripple studs above the header and the gypsum board attached to them. It needs a strong enough connection to transfer load to jamb studs. Jamb studs must, likewise, be designed for greater loads than ordinary studs. Stronger members have traditionally been detailed by the project engineer and built up in the field using combinations of stud and track.
A typical box header is built by screwing or welding together five pieces of studs and track. It’s a labor-intensive process that’s not standardized. The configuration and quality of these headers can vary considerably from worker to worker. Onsite cutting and construction raises time and labor costs, wastes material, and adds job site safety risks.
Built-up headers lower the framing’s consistency, quality, and reliability. Gypsum board or exterior sheathing may not lay flat on top of metal-over-metal overlaps created by tabs on built-up headers with screw heads protruding from them. Bulges in wall surfaces result in a noticeable finish unevenness and the need for extra remedial work.
A code-approved pre-fabricated header with an internal attachment clip to connect it to the jamb stud solves all these problems. It standardizes both the header and the connection. It eliminates fabrication labor, and the safety hazards and waste associated with it.
The attachment clip is screwed to the jamb stud. The header is then snapped over it and screwed in place permanently in the recessed channels. An optional, mated, snap-in stiffening insert for the header is available for wide openings or high loads.
A clip system changes header installation from a two-person job to a one-person job. Instead of two workers to hold the header level up and screw it into place, one worker installs the clips, and then the header snaps into place. The clip system eliminates metal overlapping metal and protruding screw-heads on the wall surface. It improves the wall finish and can avoid complaints about bulges.
The pre-fab header can equal the strength of a built up header while using less steel. Built-up elements achieve much of their strength because of bends in the metal that stiffen it against buckling—effectively creating mini-beams within the member’s larger planes. Conventional U-shaped track has two bends; C-shaped studs have four bends. The pre-engineered ProX Header system has a modified W-shape with 14 bends, so a single piece can be the entire header in a doorframe’s RO. The W’s legs function as the top track of the header. For very wide openings (more than 7 feet) or situations with high loads, it can be stiffened further with a snap-in, W-shaped insert. The insert is placed inside the multi-bend header with the W inverted, so the two Ws together form a rough X-shape with 28 bends.
Additionally, such systems can have environmental benefits. A single-piece header can use 40 percent less steel than built-up members. It reduces materials wasted in cutting, as well as reducing job site waste. Since it does not require welding, it eliminates the associated toxic gas emissions.
WIDE FLANGE JAMB STUDS
Conventional jamb studs, built up by screwing or welding two or more studs together, can cause installation problems. If assembled before installation, the part of the stud that gets attached the hollow metal frame is sealed off from access. One can cut holes through one of the studs to make frame attachments from inside the stud assembly, but this can present difficulties in inspection and cause additional work. It has been known to prompt an inspector to insist the HMF be connected to half the jamb-stud and inspected, and then have the second part of the double-stud assembly welded together in place. This halts all work around the door opening, can delay other trades, and calls for increased fire protection because of in-situ welding.
Pre-engineered wide-flange jamb studs can save considerable time and materials. The open side of the C provides continuous access and easy inspection, and is accessible for full insulation. (Built-up headers and jamb studs often create a 4- to 6-inch void in the insulation around the doorway.)
Another area of design benefitting from innovation is the top-of-wall connection to the deck above. In a non-load-bearing wall, a gap must be left between the top of the studs and the deck, to allow the deck to move down without crushing the studs or ripping them apart. The gap is a minimum of 1/2 inch.
Traditional solutions have involved either long-legged track or double-track. Long-legged track has vertical legs 2 or 2 1/2 inches long. The stud top ends are simply inserted in the track but not secured. To prevent the studs from twisting out of alignment and losing structural value and comply with ASTM C754, a piece of cold-rolled channel should be inserted through knock-outs in the stud at 6 inches or less from the top of wall, a time-consuming process. The double-track solution has a standard track screwed to the top of the studs, and a second, customized, wider track placed over it and attached to the deck overhead, so the standard track can slip up and down inside the custom track. Installing two pieces of track is expensive. Moreover, most track actually leaves as little as 1/4 inch movement clearance between the stud-securing screw heads and the edge of the top track, so the system doesn’t work in practice.
A specialized slotted track such as SLP-TRK Slotted Tracks is an appropriate solution. It is fixed to the underside of the deck, and the tops of studs are secured with screws through the slots—in compliance with ASTM C-754—allowing 1 inch up-and-down float. In fire-resistive walls, this floating connection must be fireproofed, and specialized top-of-wall elements may include standardized, code-approved, fire-resistive assembly details.
Using these three innovative products and other specialized framing accessories may slightly increase material costs. However, the reductions in labor cost and time, plus savings on approval and inspection time, possible reworks, and job delays, can result in significant overall savings on framing costs. W&C