Impact Insulation Class (IIC)

IIC – What Is It?

In a multi–level home or business, when a floor covering in one of the upper rooms is impacted, by dropping an object or moving furniture for example, the impact creates a vibration that travels through the floor, subfloor, and through the ceiling to the room below. These vibrations result in unwanted and annoying sounds in those rooms. This is called impact sound transmission. Floor coverings with a high IIC rating help to reduce impact sound transmissions to lower levels, thus reducing or eliminating those bothersome noises. The lowest IIC rated floors/ceiling assemblies come in at around 25 and the highest rated systems can come in at 85 and up.

Common Guidelines to use when selecting the proper IIC rating for your space:

IIC 50 – The least amount of impact sound transmission reduction considered effective. Some occupants would be dissatisfied with this level of sound transmission.
IIC 60 – Considered a medium level of impact sound transmission reduction.
IIC 65 – Considered a high level of impact sound transmission reduction that would satisfy most occupants.

How IIC Is Determined

The IIC rating is the determined by using a standard tapping machine with five–steel faced hammers to strike a test floor material, generating sounds between 125 Hz – 4000 Hz. The impact creates vibrations that travel through the flooring and produce sounds on the other side. Depending on the amount of impact sound that is lost during the transmission, the results from each tap are plotted on a graph. Depending where those points fall on the graph, they are compared to a reference and the IIC rating is determined.

The IIC rating can be tested in one of two different environments: Each floor covering product can be tested individually and given an IIC product rating based on that test, or can be tested as part of an entire floor/ceiling assembly. The latter can include not only the floor covering (carpet, hardwood, tile, etc.), but also the subfloor, underlayment, flooring joists, ceiling below, as well as adhesives and sealants that may be needed for installation. In addition, there are plenty of other sound–deadening materials that are used in floor/ceiling assemblies. For example, fiberglass insulation and resilient channels can be used to increase an IIC rating. In these tests, the entire floor/ceiling assembly works together to result in the structure's overall IIC rating.

The most appropriate and accurate way to measure the IIC of a home or building is to do so after installation. This way, all materials are taken into account for and given a total IIC value. Also, any air vents or other obstacles that sound can travel through are also accounted for with this method. This method is also known as the Field Impact Insulation Class (FIIC).

Other Helpful IIC Info

The easiest way to reduce impact sound transmissions is to cushion the blow. For example, carpet with a high quality pad is considered one of the most effective impact sound transmission reducers. Other resilient floors such as vinyl, cork, and rubber have slight give which cushions blows and also helps to increase the IIC rating. In addition, "floating floors" such as hardwood or bamboo installed over a resilient underlayment also helps to increase the IIC rating of the finished floor. Quite the opposite, concrete covered directly with hard, unforgiving surfaces such as ceramic tile, stone, hardwood, and bamboo can create quite a noisy surface to walk on. This is because there is no give in the floor system.

It is important to note that because the IIC scale measures sounds that are within the range of a human voice, the scale does not include noises that are below 100 Hz. This can include the light "thudding" often heard when someone walks across a floor with a lightweight joist system in the room above. Though these thuds are a very low range, they still can be bothersome to the person in the room below. The IIC also does not account for the squeaking, rattling, or crunching sounds that are the result of walking on a loose joist construction.

Flooring Joists And Concrete Subfloors

There is no easy way to accurately determine the projected IIC rating or a floor covering until it is installed and tested in the field. A large reason for this is the different types of subfloors – concrete or wood joist, which can have a large effect on the IIC rating of the floor covering. In addition, other sound deadening materials (an underlayment for example) can add to the IIC rating. To give you a better idea of the difference these factors make, the tables below show estimates of the excepted IIC ratings that you may achieve with the type of floor system shown. The first table shows floor coverings tested over concrete subfloors and the second table shows floor coverings rated over a basic floor joist system.

Table 1: Approximate IIC ratings for a 150–mm–thick concrete slab with various kinds of toppings. (Only part of the basic assembly is shown.)

Ref	Diagram	Topping	IIC Rating
1–1		None, or ceramic or marble tile	28
1–2		Vinyl flooring	35–40
1–3		Hardwood flooring	30–35
1–4		9–mm–thick hardwood on 5–mm–thick resilient layer	45–50
1–5		16–mm plywood or OSB on 40– x 90–mm wood strapping on 25–mm mineral fibra board	50–55
1–6		35–mm concrete on 25–mm mineral fibra board	60–85
1–7		Carpet and underlay	75–85

Table 2: Approximate IIC ratings for a basic joist floor (ICC 45) with different floor toppings. (Only part of the basic assembly is shown.)

Ref	Diagram	Topping	IIC Rating
2–1		Ceramic or marble tile	40
2–2		Vinyl flooring	47
2–3		Hardwood flooring	47
2–4		9–mm–thick hardwood on 5–mm–thick resilient layer	47
2–5		16–mm plywood or OSB on 40– x 90–mm wood strapping on 25–mm mineral fibra board	55–68
2–6		Resilient flooring on 35–mm concrete	52
2–7		35–mm concrete on resilient layer	55–65
2–8		Carpet and underlay	75–85
2–9		Carpet and underlay on 35–mm concrete	>85

To learn more about increasing the IIC rating of a floor/ceiling system, visit FindAnyFloor's^® section on Sound Controlling Floor/Ceiling Materials.