Industry and government standards have been established in an effort to ensure comfortable noise levels in both residential and commercial buildings.
Sound Transmission Class (SCS) is the most common acoustical rating. STC evaluates acoustical performance based on how effectively doors, walls and floors block noise from adjoining rooms. The STC system is measured in dB and is based on a series of ratings determined by ASTM International. The rating represents the difference in dB between the source room and the receiving room. An STC-55 rating or above is considered a high-quality building or luxury multi-family unit where residents expect relative peace and quiet. An STC-50 rating has been designated in model building codes as the minimum allowable design rating for unit-to-unit multi-family construction.
Impact Insulation Classification (IIC) is measured in dB and determines the sound impact from floor to ceiling in a structure. IIC is not used to measure airborne sound penetration or absorption in walls. The IIC rating increases with improved performance of the floor, its component sub-flooring, the ceiling materials as well as the framing and insulation separating the two.
Noise Reduction Coefficient (NRC) is measured in percentages where the number 0 is no absorption and the number 1 (100%) is total absorption of the sound tested. The test is performed by placing the material on the floor in the test room and measuring the absorption of sound when the material is exposed to four frequencies: 250 Hz, 500 Hz, 1000 Hz and 2000 Hz. NRC is not used to measure total assemblies.