In this article I compare acoustical performance and STC of two similar assemblies, one with 25 gage steel studs, one with wood studs. Both assemblies have two layers of 5/8” drywall with Green Glue between layers on one side and one layer of 5/8” drywall on the other side. Stud spacing is 24 inches and stud cavities are filled with fiberglass insulation.
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Test results provided by Orfield Laboratories Inc. in the table below show sound transmission loss (TL) at 1/3 octave frequencies, and the overall STC value (data taken from [1]).
Frequency [hz] |  TL [db] steel |  TL Wood [db] | TL STEELE - TL WOOD [DB] |
|---|---|---|---|
80 | 20 | 20 | 0 |
100 | 26 | 22 | 4 |
125 | 32 | 33 | -1 |
160 | 39 | 39 | 0 |
200 | 45 | 41 | 4 |
250 | 48 | 44 | 4 |
315 | 51 | 44 | 7 |
400 | 53 | 45 | 8 |
500 | 57 | 47 | 10 |
630 | 59 | 49 | 10 |
800 | 62 | 54 | 8 |
1000 | 63 | 56 | 7 |
1250 | 63 | 57 | 6 |
1600 | 61 | 56 | 5 |
2000 | 56 | 52 | 4 |
2500 | 55 | 52 | 3 |
3150 | 60 | 58 | 2 |
4000 | 64 | 64 | 0 |
5000 | 66 | 68 | -2 |
STC | 56 | 52 | 4 |
Conclusion: Steel Studs vs Wood Studs
Accuracy of test results: Test data for the wood stud assembly provided by the Orfield Lab shows that 95% confidence range for frequencies 200 Hz and below is about 1.25 dB. At higher frequencies 95% confidence range is about 0.5 dB. No accuracy specification is available for steel stud data, but it is reasonable to assume that it is similar. Therefore, differences up to 2.5 dB at low frequencies and 1 dB at higher frequencies could be strictly a measurement error.
Here are two examples for assemblies with studs on 16” centers, without Green Glue [2]:
ASSEMBLY | Steel Stud STC | Wood Stud STC | STEEL - WOOD STC |
|---|---|---|---|
one layer of 5/8” drywall on each side | 47 | 36 | 11 |
two layers of 5/8” drywall on each side | 55 | 38 | 17 |
You can see that steel studs provide 11 STC points improvement with single layer drywall, and 17 STC points improvement with double layer of drywall.
Another point to note is that the results apply only to non-load bearing steel studs gage 25. Load bearing steel studs gage 20, or lower, perform about as well as wood studs.
You will find links to acoustical data for many assemblies in our main page.
References
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