Metal Architecture Home

Light-Gauge Framing

The right frame of mind: Enhance metal paneling systems with framing

Over the last few years, there has been much focus on the energy efficiency and green aspects of metal roof and wall paneling. But how often do you think of the framing underneath? It's probably not much unless you are an engineer or maybe an architect. Nonetheless, the framing of a typical roof or wall system can often account for half of the weigh of the assembly. You certainly would not try to achieve all of your project's sustainability goals with half of your materials. So, let's examine a few avenues where using the right framing system can really enhance what your metal paneling system is accomplishing for you.

 

Generally, framing is classified as either primary or secondary. Although the line between the two is somewhat blurry, for the purposes of this article, the secondary framing is the framing that immediately supports the panel. Some examples include studs, girts, purlins and joists. Primary framing is everything else.

There are two basic strategies to employ in making a project sustainable from a materials standpoint. The first one most people logically apply is the use of sustainable materials. Steel, with a recycled content of at least 25 percent and often in excess of 50 percent, is a good choice. Certainly, LEED has recognized the importance of this in the Material and Resources section. However, the second approach, although simple, is completely overlooked by LEED. The concept is simply using as little material as possible. But this is important because it is one area where sustainability and cost-effectiveness work nicely together. Consider for a moment how often you see studs spaced at 16-inch (406-mm) on-center. It's probably frequently. One reason is because the drywall comes in 48- by 96- inch (1,219- by 2,438-mm) wide sheets and 16-inch spacing stays on module. However, if you are using a finish system, such as a metal panel system, that is available in other widths, think of how much material you could save in a building with many partitions by spacing the studs 18- or 24-inch (457- or 610-mm) O.C. No matter how sustainable your material is, using less always helps.

 

Planning for a least-weight secondary framing system can help from an energy efficiency standpoint too. Metal studs, being good conductors of heat, represent thermal bridges. These bridges allow heat to flow around the insulation, defeating its purpose. Energy efficiency codes like ASHRAE 90.1 compensate for this by mandating an "in-place" R-value for a steel stud assembly that is less than the R-value of the encapsulated insulation. Reducing stud spacing in this scenario also helps. As an example, consider a6-inch (152-mm) stud wall with studs spaced 16-inch O.C. Between these studs is R-19 (6-inch) fiberglass batt. According to ASHRAE90.1, the in-place R-Value is 9.17. Increasing the stud spacing to 24-inch O.C. gives an in-placeR-factor of 10.64, a 16 percent increase.

 

That having been said, using less material is often a challenging thing to do. Take the previous example of studs. From a structural standpoint, there has to be enough material to allow the building to support code required loads, both in interior and exterior partitions. There are also fire safety concerns because the assembly you ultimately use has to match the fire-tested assembly. From the beginning,the structural engineer and the fire safety expert have to be aware of this project goal to plan accordingly. If they are given that information earlier rather than later, they will have sufficient time to do the extra design work or research to accommodate the goal.

Another excellent opportunity in primary framing systems is the use of built-up sections. This is common practice in the metal building industry. Hot-rolled sections, although readily available in a variety of sizes, have two disadvantages. First, they have to have symmetrical flanges. In effect, you have to size both flanges for the most stringent requirement of either one. Secondly, hot-rolled sections have to be prismatic, or the same cross section through an entire length. Built-up sections, on the other hand, can be tapered and have non-symmetrical flanges, allowing a large decrease in weight for a section providing the same strength. Furthermore, the webs on most hot-rolled sections are underutilized for most real-world applications. Add to this the fact that built-up sections can easily have staggered flange and web splices, and you've got an excellent least-weight solution. Again, minimizing material minimizes the impact on the environment.

The best way to take advantage of this approach is to ask your suppliers for help. Many providers of metal construction materials have design services and do product testing. Nobody will know how to minimize material better than they will. Put them on a project team with the engineer and architect and you will have the experts in place to minimize cost and the environmental impact of your construction projects.

 

Robert A. Zabcik, P.E., LEED AP, is the technical director of the Green Building Initiative for NCI Group Inc., Houston. For more information, visit www.ncilp.com/green.