Non-Structural Metal Framing Studs vs. Structural Cold-Formed Steel
Non-structural metal framing studs, also referred to as interior studs, are thinner and not as robust as structural cold-formed steel framing. They are intended for interior use, whereas structural studs are used for exterior or load bearing applications.
Non-structural metal framing should only bear the weight of the metal framing itself and the attached materials. It is used primarily to divide up interior spaces and is meant to resist an interior wind pressure of 5 pounds per square foot (psf). Some designers may use 7 or 10 psf, but 5 psf is the code standard.
Many manufacturers will roll non-structural metal framing shapes differently. For example, Clark Dietrich’s 20 gauge interior stud measures 18 mil in thickness. These studs feature dimples (or impressions) to provide more rigidity, whereas the web and flanges of structural studs will be smooth and flat.
Non-structural studs often have a thinner galvanized coating since they are within an interior environment and therefore don’t need as much corrosion protection. Structural studs typically have a G60 coating, though it can be as high as G90. Non-structural studs often have a galvanized coating of G40.
Interior framing is limited in its width; it is available down to a depth of 15/8” and up to 6”; the stud flanges for all stud sizes are 1¼”. While structural stud shapes can be custom rolled, non-structural studs like Clark Dietrich’s pro studs are locked into certain dimensions because their allowable spans are a result of testing those specific sizes. You cannot get the customizable shape for a non-structural stud that you could with a structural stud.
If you need an interior stud that is 8” or larger, you will have to use structural stud framing.
Non-Structural Metal Framing Challenges & Considerations
- Fastening Studs to Track: The biggest mistake we see is not using a deflection track when it’s needed at top of walls. This happens when the contractor rigidly ties a stud top of wall to the track, which means there is no accommodation for movement (such as snowfall on a roof or people walking on floors); a roof, for example, can move as much as 1” vertically. This can result in cracked drywall and costly repairs. A deflection track should be used to accommodate movement.
- Strength of Steel: There are typically two strengths of steel when it comes to structural studs: 18 and 20 gauge are often made with 33-KSI steel; 16-ga and heavier will be 50 KSI. Using Clark Dietrich as our example, the heaviest non-structural stud is the ProSTUD® 33, which is 20 gauge, 33 mil, and 33 KSI. The ProSTUD 30 is 30 mil and also uses 33 KSI steel. The ProSTUD 20 can come in both 19 and 18 mil. The 19-mil track is made with 50 KSI steel. The 19-mil stud uses 65 KSI steel. The 18-mil track uses 50 KSI steel and the stud uses 70 KSI steel. The ProSTUD 25 is 15 mil and uses 50 KSI on both the track and the stud. As a designer, you have to pay attention to structural steel strength and ensure your calculations are correct.
Note: Iron Engineering does not recommend using 15 mil material because of its extreme thinness.
- Tested High Capacities: Non-structural metal studs have high capacities for their small thickness. You can easily look up load charts for a non-structural stud with no drywall and compare it with one that has drywall on both faces (at full height); you can use a composite stud design table, which means these assemblies have been fastened together, tested in a lab under different conditions, and deemed acceptable for published spans/heights. You can build further and taller with composite stud design. Note that sheathing provided on one side does not count as composite design.
- Bracing: Bracing is also a concern, even though non-structural studs are non-load bearing. Often, if you are sheathing both faces, bridging is not needed. However, it should be checked.
- Materials: Due to the size of interior openings and spaces, you may need to use a mix of materials (e.g. structural studs for heads, jambs, and sills and non-structural for typical wall studs.) Non-structural and structural materials look very different, so it’s hard to mistake one for the other.
- Screw Size: Our expert engineers recommend using a #8 screw with non-structural metal framing, as opposed to a heavier #10 or #12 screws with structural studs.
- Clips: We try to avoid using clips more often with non-structural framing. For example, headers will fasten to the jamb studs by clipping the flanges of the track, bend the web of the track, and fasten the 90 degree leg directly to the jamb.
- Shaft Wall: A shaft wall framing is for fire protection of the building structure or an occupied space. It shouldn’t be confused with non-structural metal framing. Framing of shaft wall studs is very different from non-structural and structural metal framing.
Having worked as whole building structural engineers, we know what engineers and architects are looking for, and we have extensive experience and knowledge when it comes to the intricacies and challenges of non-structural metal shop drawings. Reach out if you have questions about our cold-formed steel services, or you’re looking for a quote for your next project.