ICF As A Sound Barrier

STC Rating
Sound Transmission Class rating is a single number quantifier used to rate walls, doors, and other partitions for their effectiveness in reducing airbone sound transmission. Basically, a high STC rating indicates a more efficient sound absorption characteristic. That said, a typical wood frame wall has an STC (sound transmission class) rating of 33. ICF walls consistently achieve STC ratings of 55.

STC ratings, however, can be misleading because they are based on a logarithmic scale. The difference of around 20 in STC ratings of ICF walls vs framed walls does not mean that ICF is 60% better, but roughly four times better.

Furthermore, the actual behavior of two partitions with the same STC rating can be dramatically different, as the STC is weighted in favor of the part of the sound spectrum that represents the human voice. STC ratings are not very accurate for sound frequencies below 125Hz, a part of the sound spectrum far removed from the voice range, such as amplified music, mechanical equipment noise, or transportation noise. In practice, those are the most annoying sounds. This in mind, an ICF wall with an STC rating of 50 will perform better than a wood frame wall with insulation and drywall, having an STC rating of 50. Same STC rating, but still the ICF wall is much more effective in reducing the transmission of annoying sound.