There are a lot of options when specifying cold-formed steel framing members. Selecting the right steel stud for interior, non-loadbearing wall assemblies depends on a number of factors, including wall height, wall depth and other materials used in finishing the assembly, and are dictated by limiting heights tables published by the manufacturer or an industry association.
In 2015, the Steel Framing Industry Association (SFIA) introduced limiting heights tables for “composite assemblies” in its “Technical Guide for Cold-Formed Steel Framing Products,” based on joint testing between SFIA and the Steel Stud Manufacturing Association (SSMA). These tables allowed architects and specifiers to include the contribution of gypsum wall board to the total wall stiffness in determining the necessary thickness and rigidity of the steel framing member.
While there are certainly advantages to using composite assembly limiting heights, there are a number of caveats to understand when using these guidelines as the basis of steel stud selection, including the fact the wall board must be installed vertically, on both sides of the wall, and must go all the way from the floor to the top of the assembly. We recently sat down with Patrick Ford, technical director for the SFIA, to shed more light on the subject.
What is the definition of a cold-formed steel framed composite wall?
A composite wall accounts for the properties of the cladding as well as the stud alone. That is the simplest answer.
So then when we ask about the definition of a cold-formed steel framed non-composite wall, we’re just talking about the studs?
That’s correct. The properties of the studs alone.
Who or what defines composite v non-composite?
That one’s a little more complicated. The engineers essentially do, but the code may or may not recognize the composite wall assembly. So, it’s actually the code.
What common partition types are considered non-composite?
In reality, technically nearly all of them. Any stud partition that does not have cladding full height, and on both sides, all the way above the ceiling to the connection at the upper structure—and fastened to all framing—any of those are non-composite. If they don’t have full cladding, full height from sky to ground, they’re non-composite.
When would you choose one over the other?
The composite limiting heights are taller. It’s more efficient, the size of the steel members would be smaller, and you would save money. It’s that simple.
In a composite assembly, does the orientation of the gypsum board matter? (horizontal v vertical)
Absolutely. The composite assemblies that are listed in the limiting heights tables of the SFIA, for instance, and of virtually all manufacturers’ composite limiting heights tables, are all based on wall board that is oriented vertically. And that is based on the test assemblies that were used in determining those heights.
So, if a contractor wanted to install the wall board horizontally instead of vertically, they would have to default to the non-composite limiting height for that framing member?
That is correct. Technically they would, yes.
What is the ICC-ES AC86 testing protocol?
ICC-ES AC86 actually refers to a number of different reference standards, including AISI (American Iron and Steel Institute) standards. And we also reference the testing requirements and protocol in the SFIA appendix to our quality control program. But the ICC-ES AC86 testing protocol basically outlines how you must test these composite assemblies and how you develop the limiting heights tables from those.
Whether variables such as not having drywall fastened at a top slip track, which is commonly done nowadays, could have a significant effect on composite limiting heights, but we really don’t know. That’s the long and the short of it. It could be a huge difference, it could be no difference at all, or it could be somewhere in between. So, the SFIA is actually looking into doing tests to find out.
Does ICC-ES AC86 apply to all manufacturers as well as all associations? Why?
Oh, yes. If you want to have a composite limiting height indicated for your particular member, you have to follow it. The associations generally test to generic products, for obvious reasons, while manufacturers test for proprietary products, also for obvious reasons. But they must both meet the same criteria.
So that all member companies are testing the same way, the SFIA compliance program does require very specific details on the direction the wallboard is installed, as well as fastening and the size of the framing member. This was done to ensure all manufacturers have comparable data when the compliance administrator evaluates their data.
Contact your local ClarkDietrich technical representative for more information about our latest limiting height tests.