Installation, Specifications

Understanding sound ratings: who is IIC and what is his STC?

Author: Alex Phillips

People shopping for flooring or looking at flooring have never, and will never have to be concerned with sound ratings for flooring. But as more and more multi-family units (condos and apartments) are being replaced, the more we as flooring manufacturers are asked for sound ratings, or acoustical friendly flooring choices to meet sound requirements from design and HOA regulations. Claims of noise-proof floors and low sound transmissions are thrown around with rating numbers and promises. However, most people do not understand what the ratings mean, or even understand what information to be asking for. Sound ratings are complicated and can be misleading.

Fact One: there are two different types of sound ratings: STC and IIC. They are not interchangeable because they measure different types of sound transfer.

     – STC – refers to airborne sound that transfers through walls

     – IIC – refers to sound that transfers through the floor to the area below

Fact Two: Not all IIC or STC testing is done the same way. There are variables that can be adjusted or changed.

Example – in regards to the floor assembly under the flooring being tested; was it a concrete slab or a wood floor? What type of wood? 2×10” or 2×12” joists? Was there any gypcrete? How thick was the floor? Did the room have a drop ceiling?

When reviewing the IIC or STC ratings, provided for the flooring you are considering, make sure that you also get testing details, so you can compare apples to apples instead of apples to oranges.

Fact Three: Not all flooring types or flooring products have sound transfer testing data.

Example – many laminate floors are not tested for sound ratings because they are not typically used in applications where sound transfer is a problem.

If sounds ratings are important to you, make sure you do your homework and understand what you are looking at. But know that sounds ratings are just one of many factors that make a floor perfect or not perfect for you.

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