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Flooring 101 Home Flooring Underlayment Sound Ratings STC, FSTC, IIC, FIIC Sound Ratings

STC, FSTC, IIC, FIIC Sound Ratings

What are STC, FSTC,IIC, FIIC Sound Ratings? What do they mean?

Sound insulation products like underlayments are typically specified for condominiums, hospitals, schools, hotels, office buildings and customers desiring quieter floors. Sound control materials used for impact sound insulation are engineered to absorb and attenuate sound generated by footsteps, dropped objects etc. at the floor surface. Sound control standards were developed to regulate the amount of noise allowed to penetrate through common walls and floors within dwellings and are used to #compare product qualities. Under the current Sound rating system, the higher the number the better sound suppression quality. In other words; rooms become increasingly quiet as the rating number increases. Larger luxury Condo Associations and Municipalities typically adhere to the *International Building Code or Universal Building Code when establishing sound control standards. Many properties are now requiring sound control ratings in the high 50's or low 60's range. Local municipalities can have different rating requirements. Impact sound complaints are common on floor-ceiling assemblies that meet the bare minimum requirement of 50 decibels IIC.   

(IIC) Impact Isolation Class *ASTM E492/E989 and (STC) Sound Transmission Class ASTM E336/E413 are both tests for sound traveling through the total floor/ceiling assembly from an upper living area to a lower living area.

IIC testing is for impact noise, like footfalls, moving furniture, things dropping on the floor, etc. STC is for airborne sound like voices or music. IIC and STC tests are conducted in sound test laboratories.

It is important to understand that IIC and STC tests are not for individual components of a flooring assembly, but for the whole floor/ceiling structure, from the surface of the floor covering material in the upper unit all the way to the ceiling in the unit below. Each IIC or STC test report issued has a detailed description of the floor/ ceiling assembly used in that test. For engineered wood flooring installations, the results depend on the type of materials used in the construction of the building, along with the underlayment selected for the application.

 (FIIC and FSTC) ASTM E1007 and E989 are Field tests performed by setting up test equipment in a building. The International Building Code suggests a rating of 50 or more for IIC and STC, but allows 45 or more for FIIC or FIIC field tests.

(IIC) Impact Insulation Class, (FIIC) Field Impact Insulation Class, (STC) Sound Transmission Class and (FSTC) Field Sound Transmission Class sound testing procedures are all included in the International Building Code as official test methods for sound evaluation. There is one more type of sound that may be discussed in relation to flooring material, the sound that reverberates or echoes within the room where the floor is installed. While resonating sound is obviously important to the consumer, the ability to obtain quantitative measurements has been difficult and illusive. As of yet, there is no ASTM or ANSI method established for the evaluation of resonating sound and the International Building Code does not recognize resonating sound testing.

IIC-STC 70  Virtually Sound Proof

  IIC-STC 60   Superior Sound Proofing

  IIC-STC 50   International Building Code

  IIC-STC 40  Sound Proofing below most codes



#The ASTM E2179 'Delta' Test was developed for comparing competing Sound Insulation Products.

*American Society for Testing and Materials (ASTM)

* The International Code Council recommends that an acceptable level of performance for both STC and IIC is 55 (52 F-IIC).

The preferred level of performance for STC and IIC is 60 (57 F-IIC). An IIC and STC rating will generally be 5 points higher than

a F-IIC and F-STC rating. The IIC and STC is conducted at a controlled laboratory. The F-IIC and F-STC is conducted in the field where sound is not as controllable, hence the 5 point difference.




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Flooring 101 Home Flooring Underlayment Sound Ratings STC, FSTC, IIC, FIIC Sound Ratings