Metal Studs
A major structural concern with the use of metal studs on a concrete floor slab is the deflection in the floor that can be transferred to the exterior wall system. This design can cause the deflection stresses to pass through the studs to the single most expensive element of the wall, the outer wall material. The solution is to move the studs outboard of the floor slab and use slotted connectors to handle the deflection (Figure 7). Not only is this is a better design, it is also a less expensive solution.

Figure 7 Separating the metal studs from floor slab deflection.

Insulation
The second component is the thermal barrier, or insulation. Frequently fiberglass insulation is used in the cavity between the metal studs. While fiberglass has been tested to provide reliable thermal protection at a reasonable cost, there are concerns with its effectiveness when it is used in combination with metal studs, however. This has been documented in ASHRAE 90.1, which is the basis for many energy codes used in the U.S. (As of 2005, only 7 states do not reference this standard, while the other 43 states represent over 75 percent of the commercial construction in the U.S.) ASHRAE 90.1 requires reductions in the calculated value of the insulation by using "correction factors" (Figure 8). Note that a six-inch stud, filled with fiberglass insulation, at 16-inch centers has a theoretical R-value of R-21 but is severely reduced to only a value of R-7.4. The reason for the reduction is based on the thermal conductivity of the metal studs and the net effect on the overall heat transfer of the wall system.

Figure 8 ASHRAE 90.1 correction factors for metal stud walls.

Vapor Barrier−Retarders
This component of the wall system is climate dependent with stud cavity insulation. In cold climates, it is located on the interior of the metal studs. A key to good performance of a vapor barrier-retarder is continuity of the material, so as to avoid gaps or breaches. Challenges in maintaining this continuity occur at floor slabs, behind spandrel beams, at electrical box penetrations, and at the roof and wall intersection at parapets (Figure 9) . The condition at the parapet is critical because it relies on coordinating wall and roofing contractors to maintain vapor barrier continuity. Electrical distribution is a challenge because frequently it is done in the stud cavity. Hence, at every electrical box, the vapor barrier is penetrated, causing a breach in the vapor barrier continuity.

Exterior Gypsum Sheathing
Exterior grade gypsum sheathing is applied to the exterior side of the metal studs. There are advantages and challenges with this type of installation. Advantages include quick enclosure of the building, fire resistance, and the creation of a continuous surface to apply building wraps. Challenges associated with the gypsum sheathing material include the necessary penetrations to secure the outer material or cladding attachments, and the resulting exposure of the gypsum core to moisture.