Three Sound Ratings You Need to Know
STC, OITC, & IIC
14 September 2021
Excessive noise in schools, homes, hotels, offices, hospitals, and institutional buildings can cause loss of sleep, fatigue, elevated stress levels, and productivity issues. There are acoustic requirements and standards that should be met in every space. Through proper design and materials, the specified acoustical requirements can be achieved.
More stringent performance requirements make it necessary for manufacturers to test their products to ensure they meet building and sometimes specific project codes.
Manufacturers are required to verify their product's acoustical performance via a laboratory test. The following are three common laboratory sound ratings you should know to make sure products are up to code.
STC
Sound Transmission Class (STC) is an integer rating of how effectively an interior building element attenuates, or reduces, airborne noise from one side to the other. This is used to rate various interior elements such as walls, floors, ceilings, doors, and windows.
The rating is a curve fit calculation using the 1/3 octave sound transmission loss data generated by performing an ASTM E90 sound transmission loss test. A standard contour curve (a curve fit calculation) is fit to the test product data curve such that certain criteria are met. Once the criteria are met, the contour curve point at 500 Hertz is the STC rating.
STC is stated in the international building code and holds a minimal requirement of what is acceptable for most construction and related building codes. It is one of the most common sound ratings that plays an important role in soundproofing spaces and keeping your project up to code.
OITC
Outdoor/Indoor Transmission Class (OITC) and is an integer rating of how effectively an exterior building element attenuates, or reduces, airborne noise from outside to inside a building. It is best used to rate façades and façade elements (windows, doors, roofs, etc.).
OITC is calculated by subtracting the logarithmic summation of the transmission loss values from the logarithmic summation of the A-weighted transportation noise reference spectrum stated in the calculation standard.
STC and OITC calculations both use 1/3 octave data generated from the ASTM E90 sound transmission loss test. The difference in the data used is that each rating uses a different frequency range.
IIC
Impact Insulation Class (IIC) is a sound rating that measures the impact generated noise that is transmitted through a floor/ceiling or roof system and into the room below. These impacts can be caused by footsteps, falls, chair scrapes, fallen objects, or weather impact. IIC is calculated through tests conducted in the lab on horizontal partitions such as floor/ceiling assemblies.
IIC is stated in the international building code and holds a minimal requirement of what is acceptable for most construction and related building codes. It is one of the most common sound ratings that plays an important role in soundproofing spaces and keeping your project up to code.
Conduct These Three Sound Ratings
Ensuring your building meets the proper project and building code requirements for STC, OITC, and IIC sound ratings can ensure that your building's space offers an environment that will be comfortable for occupants and not generate complaints.
If you need testing for these three sound ratings, Intertek can help. We have been performing acoustical tests on building products since 1997. We are on the cutting edge of technology and information pertaining to acoustics. We are involved with ASTM in writing the acoustic testing standards and will test to see if your products are meeting your requirements. Contact us to learn more about how we can help.
For more education on acoustics, view our acoustic webinar series. A three-part series that discusses architectural acoustics, sound testing for specific product categories, noise sources that can affect acoustical performance, acoustical analysis, and much more.
Todd Kister
Intertek, Building & Construction, Regional Manager – Acoustical Testing
Todd has more than 24 years of experience with laboratory and field acoustical testing of building products. He was part of the design, construction, and commissioning of Intertek's horizontal transmission (HT) and vertical transmission (VT) acoustical chambers located in York, PA and Lake Forest, CA. Todd is a member of the American Society for Testing and Materials (ASTM). He serves as the chair of the E33.03 sound transmission subcommittee and numerous task groups. Todd attended Pennsylvania State University for Electrical Engineering Technology.