The right frame of mind:
Enhance metal paneling systems with framing
Robert A. Zabcik, P.E., LEED AP,
Posted
02/01/2010
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.
www.ncilp.com/green