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
| Hardwood 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) | 29 | 43 to 47 |
| Engineered Hardwood with Underlayment | 53 to 56 | 52 to 53 |
| Solid Parquet with Foam Backing | IIC: 55 STC: 51 | N/A |
| Carpet, directly applied (for reference) | Equal to or greater than 55 | Equal 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) | 29 | 43 to 47 |
| Carpet, directly applied (for reference) | Equal to or greater than 55 | Equal to or greater than 55 |
| Vinyl with no backing or cushion Vinyl Composition Tile Natural Creations Parallel Alterna | Less than 45 | 45 to 49 |
| Rotovinyls Duality Premium w/ D10 | 45 | 50 |
| Rotovinyls CushionStep Good CustionStep Better (51 over 6″concrete slab) CushionStep Best (50 over 6″concrete slab) FlexStep Good | 50 to 51 | 53 to 54 |
| Rotovinyls StrataMax Good StrataMax Better StrataMax Best | 46 to 49 | 50 to 53 |
| Products | Test Date | Report # | Type | STC | IIC | Delta IIC |
| 5mm Rigid Core | 9/5/2019 | K0853.01-113-11-R1 | Concrete Slab-152 mm | 50 | 56 | 25 |
| 5mm Rigid Core | 9/5/2019 | K0854.04-113-11-R1 | Concrete Slab-152 mm with drop ceiling | 62 | 72 | – |
| 6mm Rigid Core | 9/5/2019 | K0853.03-113-11-R1 | Concrete Slab-152 mm | 50 | 55 | 16 |
| 6mm Rigid Core | 9/5/2019 | K0853.06-113-11-R1 | Concrete Slab-152 mm with drop ceiling | 63 | 71 | – |
| Hydroguard | 9/5/2019 | K0853.02-113-11-R1 | Concrete Slab-152 mm | 50 | 53 | 23 |
| Hydroguard | 9/5/2019 | K0853.05-113-11-R1 | Concrete Slab-152 mm with drop ceiling | 63 | 67 | – |
| Bruce Lifeseal,Robbins Pro-Tekt, Hartco Everguard, LM Mariner Classic | 5/28/2020 | L0367.01-113-11-R0 | Concrete Slab-152 mm | 50 | 56 | 24 |
| Bruce Lifeseal,Robbins Pro-Tekt, Hartco Everguard, LM Mariner Classic | 5/28/2020 | L0367.05-113-11-R0 | Concrete Slab-152 mm with drop ceiling | 60 | 67 | – |
| Bruce Lifeseal Trending, Robbins Pro-Tekt Trending,, Hartco Everguard Trending, | 5/28/2020 | L0367.02-113-11-R0 | Concrete Slab-152 mm | 50 | 55 | 24 |
| Bruce Lifeseal Trending, Robbins Pro-Tekt Trending,, Hartco Everguard Trending, | 5/28/2020 | L0367.06-113-11-R0 | Concrete Slab-152 mm with drop ceiling | 60 | 66 | – |
| Bruce Turlington 3/8″ (EAK20LGEE) | 5/28/2020 | L0367.03-113-11-R0 | Concrete Slab-152 mm | 51 | 55 | 24 |
| Bruce Turlington 3/8″ (EAK20LGEE) | 5/28/2020 | L0367.07-113-11-R0 | Concrete Slab-152 mm with drop ceiling | 60 | 65 | – |
| 3/8″ Indensity | 5/28/2020 | L0367.04-113-11-R0 | Concrete Slab-152 mm | 50 | 54 | 23 |
| 3/8″ Indensity | 5/28/2020 | L0367.04-113-11-R0 | Concrete Slab-152 mm with drop ceiling | 60 | 66 | – |
| Contract Dry Back LVT | 8/2/2020 | L2325.01-113-11-R0 | Concrete Slab-152 mm | – | – | – |
| Contract Loose Lay | 8/5/2020 | L2325.02-113-11-R0 | Concrete Slab-152 mm | 52 | 44 | 16 |
| Contract SPC | 8/2/2020 | L2325.03-113-11-R0 | Concrete Slab-152 mm | 50 | 59 | 27 |
| Raintree / Forest Rain | 7/6/2022 | N9266.02-113-11R0 | Concrete Slab-152 mm | 52 | 53 | 23 |
| Raintree / Forest Rain | 7/2/2022 | N9266.01-113-11R0 | Concrete Slab-152 mm with drop ceiling | 61 | 64 | – |
| Product | Test Structure | STC | IIC | Delta 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 | 51 | 53 | 22 |
| Armstrong Flooring 3.2 mm LVT (Natural Creations) | 6 in. concrete, no ceiling, with S-1840 Quiet Comfort Luxury Flooring Underlayment | 51 | 52 | 22 |
| Armstrong Flooring 2.0 mm LVT (American Charm) | 6 in. concrete, no ceiling, with S-1840 Quiet Comfort Luxury Flooring Underlayment | 52 | 53 | 23 |