January 29, 2017

Problems with Metal Stud Construction

Metal stud construction is one of the options available to architects, designers and project managers considering which commercial wall systems to use. However, there are potential energy efficiency, safety and performance issues that arise with metal stud construction.

Limits of Cavity Insulation

Cavity insulation in metal stud walls is of limited value, largely because of the high thermal conductivity of the steel. Therefore, layers of exterior insulating board and exterior EPS, XPS or Polyiso board are typically required to achieve desired R-values.

According to the Oak Ridge National Laboratory, thermal bridging lowers the effectiveness of cavity insulation by 55 percent. That means that the cost-effectiveness of metal studs is offset to some degree by the need for additional layers of insulation.

Upgraded 2015 IECC requirements, moreover, add to the challenge presented by the thermal conductivity of steel studs.

Hazards from Smoke and Fire

As Gregory Havel states in Fire Engineering, “Since there is not much mass to the steel studs… they are as likely as steel trusses and bar joists to be weakened quickly by heat and as prone to early collapse.” Screws used in metal stud construction are also prone to early failure when they are stripped through over-tightening or when there is rusting.

Metal stud construction poses challenges for designers and architects seeking to offer clients fire-rated designs. Although four-hour fire-rated metal stud construction is possible, they require the addition of multiple layers of fire-resistant material.

Firefighters consider a metal stud wall assembly as a single void space because of the holes created at the factory to accommodate conduit, cables and pipes. These void spaces often link to voids in the floors, which may allow smoke and fire to spread. Sprinkler systems cannot douse a fire inside these voids. Fire can also spread by breaking through the drywall that would otherwise enclose the voids.

Although the idea may be somewhat counter-intuitive, metal studs may be an even greater problem during a fire than wood studs. Havel rather ominously asserts that “the heat of the fire will cause steel studs to fail more quickly than wood studs.” He further adds that if a “first attack” by firefighters is unsuccessful, there might not be time for a “second attack” before a structural collapse.

Potential Electrocution Hazard

During metal stud construction, or in the event of a fire, sharp edges pose a threat to the integrity of protective jackets on conduit and cabling. If the protective covering is compromised, the entire metal frame could be energized, posing an electrocution hazard. Although short circuits often trip circuit breakers or blow fuses, this is not always the case.

Performance Compromised by Galvanic Corrosion

Metal-to-metal contact creates the potential for galvanic corrosion, “the more noble metal will become the cathode and the more active metal will become the anode.”

These three conditions together can lead to galvanic corrosion:

  • Direct contact between two different metals (like steel and aluminum) with varied corrosion potential
  • An electrolyte solution like water routinely develops, creating a conductive route between the metals.
  • A source of moisture, including wind-driven rain, condensation, leaks or even fog.  

Electric current flowing from one metal to the other will further increase the corrosion rate.

Ultimately, galvanic corrosion can lead to unanticipated failures. During construction, wood blocks are often installed between aluminum window/door frames and galvanized steel studs to prevent it; however, improper installation can still lead to weakening caused by galvanic corrosion. Even aluminum-jacketed cables can interact with galvanized steel studs if plastic bushings are not properly deployed.

Four-hour fire rated, energy-efficient Bautex Block offers a high-performing, cost-effective alternative to metal stud construction. Click here for more information about how The Bautex System can meet your project requirements.