Acoustical Data – Impact Insulation Class (IIC) and Sound Transmission Class (STC)

Understanding Acoustical Terms

Building materials and furnishings can affect the acoustics of a building in three ways:

  • Sound Absorption: They can absorb sound, lowering background noise levels and reducing reverberation within a room.
  • Airborne Sound Transmission: They can serve as acoustical insulation and reduce transmission of airborne sounds, such as voices, between rooms.
  • Impact Sound Transmission: They can serve as impact sound insulation and reduce the transmission of impact sound, such as footsteps, from one room to another below or adjacent to it.

Hard surface flooring is acoustically significant only in the area of impact sound transmission. It will not subdue airborne noises originating from such sources as computers, telephones and conversation. Hard surface floors will have little effect on airborne sound transmission between contiguous rooms. Therefore, flooring materials do not significantly reduce the Sound Transmission Class (STC), which is a rating of airborne sound transmission loss of the floor/ceiling assembly or the partitions. However, it is important to have some understanding of generally accepted acoustical terms when talking with architects, specifiers, designers, builders and developers.

Sound Absorption

The installation of hardwood flooring will add virtually no sound absorption to a room. Sufficient sound absorption can only be supplied by other room finishes (walls and ceilings) and furnishings (drapes, furniture, etc.).

The Noise Reduction Coefficient (NRC) is the rating of sound striking the material that is absorbed rather than reflected away by the material. NRC’s range from .00 (no absorption) to 1.00 (100% absorption). Hard surface flooring has an NRC of approximately 0.03 to 0.05; carpet (1/8” pile) is 0.10 to .15. The NRC of commercial acoustical ceiling is usually well in excess of .50.

Airborne Sound Transmission

Hard surface flooring and carpet cannot significantly influence the transmission of airborne sounds, such as voices, between rooms. The determining factor is the basic construction of the building in question.

The Sound Transmission Class (STC) is the rating of airborne sound transmission. The STC of a floor/ceiling (or wall) structure is a measure of the decibel difference between the airborne sound energy striking one side of the structure and the sound energy radiated into a receiving room on the other side. Typical floor/ceiling structure STC values range from 25 to 35 for lightweight single family residential construction to upwards of 50 to 60 for commercial construction.

Impact Sound Transmission

The choice of floor covering can have a significant effect on the amount of impact sound transmitted from a room above to a room below. As in the case of airborne sound transmission, the total floor/ceiling structure strongly influences the impact sound transmission, the floor covering is also important. This is because the impact sound is generated by a shoe or other object impacting directly on the floor covering. The floor surfacing material can help cushion the impact and therefore reduce its effect on the sound transmitted to not only the rooms below, but also through the structural floor to adjacent rooms on the same floor.

The impact sound insulation properties of a floor/ceiling structure (including the flooring) are usually tested by measuring the transmitted sound in a room below while a standard “hammer machine” bangs on the floor above. The results of the test are rated in terms of the Impact Insulation Class (IIC). IIC values can range from as low as 25 for lightweight residential construction with no floor covering to over 65 for commercial construction with carpet. More typical values fall between 35 and 55. For multi-family structures, some codes require an IIC of 50 or more when tested in the laboratory (or 45 or more when tested in the field).

IIC Values and Our Floors

We have received inquiries from builders and architects about impact noise ratings of flooring over suspended concrete slabs and over lightweight concrete-capped wooden subfloors in multi-story residential buildings.
The following conclusions are drawn from laboratory testing over lightweight structures and from tests with a 6″ thick concrete slab structural floor.

Minor styling or structural differences have no significant effect on flooring IIC ratings.

Typical Ranges of Laboratory IIC Acoustical Ratings on Common Floor/Ceiling Constructions

Product Category
Approximate IIC Rating on
6″ Thick Concrete  Slab Floor
(150 lbs/cu ft)
Approximate IIC Rating On
Lightweight Concrete-Capped
Wood Floor
None (bare)2943 to 47
Engineered Hardwood with Underlayment 53 to 5652 to 53
Solid Parquet with Foam BackingIIC: 55
STC: 51
Carpet, directly applied (for reference)Equal to or greater than 55Equal to or greater than 55
Resilient Floor Covering
Category Or Other Floor Covering
Approximate IIC Rating
On 6″ Thick Concrete  
Slab Floor (150 lbs/cu ft)
Approximate IIC Rating
On Lightweight Concrete
Capped Wood Floor
None (bare)2943 to 47
Carpet, directly applied (for reference)Equal to or greater than 55Equal to or greater than 55
Vinyl with no backing or cushion
Vinyl Composition Tile
Natural Creations
Less than 4545 to 49
Duality Premium w/ D10
CushionStep Good
CustionStep Better (51 over 6″concrete slab)
CushionStep Best (50 over 6″concrete slab)
FlexStep Good
50 to 5153 to 54
StrataMax Good
StrataMax Better
StrataMax Best
46 to 4950 to 53
ProductsTest DateReport #TypeSTCIICDelta IIC
5mm Rigid Core9/5/2019K0853.01-113-11-R1Concrete Slab-152 mm505625
5mm Rigid Core9/5/2019K0854.04-113-11-R1Concrete Slab-152 mm with drop ceiling6272– 
6mm Rigid Core9/5/2019K0853.03-113-11-R1Concrete Slab-152 mm505516
6mm Rigid Core9/5/2019K0853.06-113-11-R1Concrete Slab-152 mm with drop ceiling6371 –
Hydroguard9/5/2019K0853.02-113-11-R1Concrete Slab-152 mm505323
Hydroguard9/5/2019K0853.05-113-11-R1Concrete Slab-152 mm with drop ceiling6367– 
Bruce Lifeseal,Robbins Pro-Tekt, Hartco Everguard, LM Mariner Classic5/28/2020L0367.01-113-11-R0Concrete Slab-152 mm505624
Bruce Lifeseal,Robbins Pro-Tekt, Hartco Everguard, LM Mariner Classic5/28/2020L0367.05-113-11-R0Concrete Slab-152 mm with drop ceiling6067– 
Bruce Lifeseal Trending, Robbins Pro-Tekt Trending,, Hartco Everguard Trending,5/28/2020L0367.02-113-11-R0Concrete Slab-152 mm505524
Bruce Lifeseal Trending, Robbins Pro-Tekt Trending,, Hartco Everguard Trending,5/28/2020L0367.06-113-11-R0Concrete Slab-152 mm with drop ceiling6066– 
Bruce Turlington 3/8″ (EAK20LGEE)5/28/2020L0367.03-113-11-R0Concrete Slab-152 mm515524
Bruce Turlington 3/8″ (EAK20LGEE)5/28/2020L0367.07-113-11-R0Concrete Slab-152 mm with drop ceiling6065– 
3/8″ Indensity 5/28/2020L0367.04-113-11-R0Concrete Slab-152 mm505423
3/8″ Indensity 5/28/2020L0367.04-113-11-R0Concrete Slab-152 mm with drop ceiling6066 –
Contract Dry Back LVT8/2/2020L2325.01-113-11-R0Concrete Slab-152 mm
Contract Loose Lay8/5/2020L2325.02-113-11-R0Concrete Slab-152 mm524416
Contract SPC8/2/2020L2325.03-113-11-R0Concrete Slab-152 mm505927
Raintree / Forest Rain7/6/2022N9266.02-113-11R0Concrete Slab-152 mm525323
Raintree / Forest Rain7/2/2022N9266.01-113-11R0Concrete Slab-152 mm with drop ceiling6164
ProductTest StructureSTCIICDelta IIC
Armstrong Flooring 2.5 mm LVT (Biome, Coalesce, Terra, Theorem, Exchange,
Duo, Unity)
6 in. concrete, no ceiling, with S-1840
Quiet Comfort Luxury Flooring Underlayment
Armstrong Flooring 3.2 mm LVT (Natural Creations)6 in. concrete, no ceiling, with S-1840
Quiet Comfort Luxury Flooring Underlayment
Armstrong Flooring 2.0 mm LVT (American Charm)6 in. concrete, no ceiling, with S-1840
Quiet Comfort Luxury Flooring Underlayment
Updated on April 28, 2023