Envelope #20: How to quickly determine the allowable height for interior, non-bearing, metal stud partition?
Happy Thursday! Welcome to Back of the Envelope. This is email #20! My goal is to get to at least #50, then decide if I should continue. For now, let’s talk about some metal studs!
Here is a scenario that happened recently.
A client called up and asked:
Hmm good question.
Let’s dissect that and come up with a solution in 2 minutes and 15 seconds!
What do we know?
1/ First, we know there are gypboard on both sides, so studs are considered fully braced.
2/ Interior non-bearing wall means we must design it for at least 5 psf lateral load.
3/ 3-5/8” x 20ga non-bearing stud means the member designation is 362S125-33. (for more info, see SFIA documents)
4/ The finishes are brittle, so the deflection criteria is L/240.
What are the constraints?
1/ Floor plan is pretty set-in-stone, so changing to 4” or 6” studs is not ideal.
2/ Using a thicker gauge is also not an option since steel transmits sound waves – a heavier gauge actually lowers the STC rating.
In other words, we need to increase the spacing but can’t increase the depth nor the gauge. Interesting challenge – how do we do that?
Oh, by increasing the flange width, you say? Smart. Thanks batman.
362S125-33 @ 16” non-composite
First, I was curious to see how close we are with 362S125-33 @ 16”.
Pulling up SFIA table (equivalent-ish of SSMA) for “Interior Non-Structural Non-Composite”:
The maximum height is only 15’-5”… not quite close to the intended 16’. Perhaps the architect had specified the proper assembly to allow for composite?
Let’s see if that works.
362S125-33 @ 16”o.c. composite
Pulling up SFIA table for “Interior Non-Structural Composite”:
Alright, that’s better (assuming the correct screw, spacing, etc., are specified).
Now, how close are we using the same stud but at 24”?
362S125-33 @ 24”o.c. composite
Short by 9”. Let’s try 2” flange instead of 1.25”.
362S200-33 @ 24”o.c.
Since the size is not typically used for non-structural applications, it’s not listed on any of the “non-structural” tables. We have to use the Curtain Wall (Single Span) table instead.
Strangely, SFIA doesn’t list allowable height for 5 psf, so we have to open up the SSMA technical guide (maybe we should’ve done that since the beginning…):
That worked for 16’. And the height is based on non-composite so we are all golden.
Well, that was fun – looking up tables without running numbers is nice sometimes.
And what if I tell you, there is even a quicker way?
ClarkDietrich has a suite of free online tools to help you specify their proprietary studs – but part of it also includes a lookup filter for generic studs.
Check it out here: (link)
First you enter all the good stuff that we just talked about:
And the online app automatically gives you the sections that work!
Alrighty that’s all for now – thanks for reading. Let me know if you have any questions and I can perhaps cover them in future emails.
Have a good one!
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