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What Is Impact Insulation Class & What’s a Good IIC Rating?

Impact Insulation Class

Are you tired of hearing the footsteps of your upstairs neighbor on your ceiling, or are you tired of hearing them move their furniture around?

Have you also heard complaints from your downstairs neighbor about noises coming from your room?

Well, have we got the solution for you! Sit back and save your energy.

Stick around to know more about what a good IIC rating is, how you can identify it, and how to improve your floor IIC rating (like adding a flooring underlayment to your floor’s assembly)

Let’s get right to it.

Table of Contents

What Is Impact Insulation Class?

Soundwaves generate noise. In the soundproofing world, the end goal is to hear sound and avoid the noises. To add, there are trillions of dancing sound molecules suspended in the air around you!

Impact insulation class (IIC) describes how easily sound waves can penetrate through an upper floor to the floor below it. This also describes the overall assembly of the construction.

Illustration of Impact Noise

To understand what this means, there are some things you need to learn first!

There are two types of noise: Airborne and impact noise.

  1. Airborne noise is transmissions made through the air. Examples of airborne sound would be a person’s voice and echoes.
  2. Impact noise, on the other hand, is a sound transmission that travels through solid materials. Examples of impact noises are a ball bouncing on the floor above you and footstep vibrations.

Impact noise will travel through a layer of the structure that DOES NOT have a resilient material as part of the construction assembly.

Impact insulation class will help with these because these are acoustical soundproofing ratings that quantify vibration isolation.

Examples of Materials With Good Impact Insulation Class (IIC)

Acoustical floor underlayment is a material made up of extruded nylon filaments that form a 3-dimensional core with a non-woven fabric heat-bonded to its upper surface.

This underlayment has an impressive rating for all assemblies but carries no sound transmission class (STC rating) as stand-alone material.

Joist floorings also offer a better layer of noise support than concrete flooring.

Overall, these help structurally isolate the top layer of the floor from the rest of the components.

Explaining Impact Sound

Impact noise occurs when an object hits another object. This then generates sound through the building.

Soundproofing your floor and subfloor is BEST to avoid impact noise from transmitting from one room or level to another.

How Can Impact Noises Be Reduced?

One way is to utilize soft carpet, pad cushions, plywood that are thick, so that middle to high-level frequencies can be significantly reduced.

Another way to reduce impact noises is to opt for floor soundproofing that should be placed underneath the finished flooring and should cover the whole floor.

What’s a Good IIC Rating?

A good impact insulation class (IIC) is an acoustic rating that will rate how well a floor assembly blocks impact vibration.

The International Building Code requires most public structures ceilings and floor assemblies to have IIC ratings of at least 50.

IIC STC Ratings Chart

IIC ratings for floor-ceiling assemblies above core learning spaces should be at least IIC-45 and preferably IIC-50 (measured without a carpet on the floor).

Some assemblies, especially those with flooring underlayment, can reach an IIC rating in the 80s.

As much as possible, you should strive for this number to achieve the most comfortable environment!

How to Determine Good IIC Ratings

There are several factors to look into, such as the substrate, the finish of the flooring, and the soundproofing underlayment.

The more impact sound is reduced if the rating is higher.

You can use this installed IIC calculator to determine a good rating.

What Is the Highest IIC Rating?

As we said, ICC is how easily sound waves can travel through an upper floor to the floor below it. It also gives a clearer picture of the overall assembly of the construction.

An IIC rating of 50 means that the material used for your flooring has MINIMAL sound absorption capabilities.

The midrange IIC rating is 60. The materials included in these are some vinyl flooring as well as wood and laminate floors.

The highest IIC rating can reach up to 80.  The materials included are cork flooring and carpet.

Underlayments installed under these materials absorb noise footfall, preventing noise from transferring to the ceiling below.

This means that the higher the rating is, the more sound is blocked!

How Do You Calculate Impact Insulation Class Ratings?

An IIC rating calculates the sound-blocking ability of the floors assembly. The floor assembly includes everything that makes your floor — the joists, subfloor, underlayment, and floor covering.

To add, the ratings determine the ceiling’s soundproofing ability.

You can test this out at home yourself, although you can directly purchase and have products installed that have undergone testing.

Here’s how professionals check the floor’s IIC. 

  1. They use a tapping machine with steel-faced hammers, then strike the floor to generate impact noises.
  2. After this, they calculate the number of impact sounds lost during the process and plot it onto a graph.
  3. Finally, the professional will reference those calculations and plot points to identify an accurate IIC rating.

Tips on How to Improve Your Floor’s IIC Rating to Better Control Noises

The transmission of vibrations and noises can take up your energy.

For instance, this is often realized in the real world as a “neighbor sound” generated from someone walking on the floor above or other activities.

Here are some tips on how soundproofing through underlayment can help your floor’s impact insulation class absorb sound within a given space.

#1 Mechanically Remove All Traces of Old Debris

You should mechanically remove all traces of old debris by scraping or sanding these adhesives or old paint away.

#2 Fill With Patching/Leveling Compound

All saw cuts (control joints), cracks in the concrete must be filled with an approved patching/leveling compound.

#3 Allow Material to Dry Thoroughly

Allow material to dry thoroughly because any concrete subfloor can be a source of moisture-related flooring failures.

NOTE: You can work on this without having to worry about the need for adhesives or expensive tools

Why Is IIC Important?

If you have ever lived in a multi-story house or apartment, then you know how bothersome the vibration from the upstairs unit can get.

The assembly of the underlayment of your flooring is VERY important to reduce the amount of disturbance you hear and make.

It would be best if you took concrete actions to ensure that the area you live in is a place where you can relax.

You can check out our tips on how to improve the IIC of your floor!


The material and components used during the construction of your space are VITAL.

To save you time and energy, it is important to research different materials with the best impact sound insulation you can get out there!

You’ll feel much better and at peace once you get the right underlayment and assembly for yourself.

Say goodbye to unwanted vibration or walking sounds from the upstairs unit!

About the Author


Andrea has always been bombarded by the hustle and bustle outside her home. Living in the city doesn’t get any quieter. The never ending noise from construction, traffic, and dogs barking on the streets day in and day out drove Andrea to a breaking point.

For 3 years, Andrea committed herself to studying DIY hacks, performing soundproofing experiments, and installing noise-free solutions. Now, she lives a quiet life free of the stress from noisy environments.

She hopes to share this knowledge so that others don’t have to endure the noise reigning in their ears and live a peaceful, stress-free life.