IIC stands for Impact Insulation Class, which refers to impact sounds such as shoes hitting the ground, dropping a cell phone, or other scenarios where something it dropped or impacts the floor. STC stands for Sound Transmission Class, which refers to any audible noise (not an impact) such as music playing aloud, a conversation, or a loud television, for example. With both of these ratings systems, the higher the number rating is for the underlayment, the better it will suppress sound, and the quieter a room will be. You may want to pay close attention to these ratings when shopping for underlayment if sound reduction is important to you.
Why use underlayment?
Underlayment is a great product solution that will work to help reduce impact noise like footsteps between floors of a building, as well as adding thermal properties and a little bit of cushion so that your tootsies stay comfortable on your new flooring.
Is noise really an issue?
There are two types of potential acoustical issues that you might face in a home or business: sound transmission between multiple rooms or floors, and room acoustics within a single room interior. Noise is a very important factor in a variety of spaces, such as in hotels, hospitals, multi level apartment complexes, homes with a quietly sleeping newborn, call centers, you get the point.
I don’t want a loud, echoey house. What is the best floor to reduce noise?
Consider how reflective the flooring surface will be. Harder, more rigid products such as tile, stone or hardwood will be more reflective than soft/fibrous floors.
What can I do to make it quieter once my flooring is installed?
If you have a hard surface flooring, to increase the effectiveness of impact sound reduction, you should consider adding an area rug or runners in hallways and spaces that receive a large amount of foot traffic. It really helps to think of sound reduction as a whole ‘system’ rather than simply a ‘one piece’ solution.
What are the ratings and what do they mean?
IIC, or
Impact Insulation Class, is a rating of how well a floor-ceiling assembly lessens
impact sounds or
structure-borne sound transmission (think of noisy footsteps upstairs, or a dropped remote hitting the floor). This number can be significantly affected by the choice in a floor covering and/or an underlayment.
Example: carpet (an absorptive floor option) can help to absorb and lessen impact noises, compared to a tile floor (a reflective floor option) that is very hard and would hit loud and bounce the noise. More rigid materials will be less effective than soft, fibrous materials.
STC, or
Sound transmission Class, is a rating of how well a wall or floor lessens
airborne sound (think of a cranky teenager blasting their loud, angry music). STC rating numbers are minimally affected by a floor covering and/or an underlayment. (Time to think of building a soundproof room for those music sessions!)
NRC, or
Noise Reduction Coefficient, is a measure of how
absorptive a finish is, or how much sound is absorbed by a finish when the sound comes in contact with it. Smooth surfaces typically have a lower NRC rating (more ‘bounce’) and are not as absorptive as carpet, acoustic wall treatments, or ceiling panels. Think of the last time you were in the movie theater - it had carpeting and the fancy wall panels to absorb sound. This prevents the audio from bouncing around and becoming echoey.
