Impact Isolation Class and Other Friends

My understanding of impact isolation is that you typically want an assembly/material with a higher impact isolation class rating. Therefore if you had to pick between concrete and wood as a floor assembly material you would go with concrete cause it has a high IIC rating? (I could have this backward, please correct me if I got this mixed up)

In general when it comes to good sound absorption, what factors below do I want high or low?:
STC Ratings
SAC/NRC (I know these are coefficients and not necessarily ratings)
IIC Ratings

I think we want all of these to be high for good sound “design” in that I won’t be able to hear my noisy neighbors in an apartment building, but I often find myself getting the terms confused.


Hi @Shikha ,

Great question! I dealt with noise reduction a lot in the past while working on hotel projects.
The best resource I’ve found for comprehensively understanding the topic is actually CEU courses. The link below will take you to one of Rockfon’s CEU courses on the topic of sound transmission. I attended this in person awhile back and found it incredibly helpful!

Acoustiguard’s website also does a great job describing these concepts:

STC is used in wall assemblies most often to represent the walls ability to stop sound transition to the other side.

NRC is used to rank a material’s ability to absorb sound. The higher the value the more absorbent a material is.

IIC is used to understand how much noise transfers from the floor above to the ceiling below, for instance when someone is walking on it.

In your example above, a wood floor on wood joists with no ceiling assembly will have a low IIC value and you will hear everyone walking above. A concrete floor (for instance, metal deck with concrete topping on hollow-core planks or the like) will have a much higher IIC.
However, more so than anything else, absorptive surfaces like insulation or cork are going to allow for higher IIC ratings.

Hope this helps,

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