Sound Ratings: STC vs. OITC ratings

October 14, 2014

by admin

aama, insulated glazing unit, interior windows, laminated glass windows, oitc, sound control, sound control windows, sound ratings, stc

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Sound ratings were developed by the American Architectural Manufacturers Association (AAMA) and the American Society for Testing and Materials (ASTM) to standardize the testing and rating of sound transmission for building components, particularly windows. Two sound ratings are mainly used: sound transmission class (STC) and outdoor indoor transmission class (OITC).

STC vs. OITC ratings

STC is typically used to measure sound transmission loss over a frequency range from 125 to 4000 hertz, and is most applicable for interior areas that experience mid to high frequency noises, such as conversation, television, or office equipment. OITC is similar to STC, but is measured for exterior areas across a frequency range of 80 to 4000 hertz and is therefore more applicable for low frequency noises coming from urban environments, such as traffic or airport noise. In the case of both STC and OITC ratings, a higher the rating, the better as it indicates that less noise is detectable.

What is considered an acceptable rating for STC and OITC?

The amount of nearby noise will typically determine what constitutes an acceptable STC and OITC rating. Archtest results typically show IGUs in the 20s and 30s range for STC. When a third panel is placed behind an insulated glazed unit (IGU), Archtest shows values up to 46 STC. In our recent tests, an annealed IGU was used as the primary window and was tested. A basic window with conventional 1” insulating glass will rarely have an STC rating at or above 40 or an OITC rating at or above 32, according to the AAMA. This may suffice for low noise environments. To put the ratings into context, an area with high traffic or airplane noise volume may require an STC of around 43 and an OITC of at least 36 to maintain a comfortable sound environment.

Thermolite’s RetroWAL™ interior curtain wall retrofit system has measured at an STC of 47 and an OITC of 40, which exceeds any Arc Tests previous results. In comparison, an average baseline curtain wall has been measured to have an STC rating of 26 and an OITC of 31. Request to view detailed reports.

This is a significant increase in sound improvement with a nearly 50% reduction in perceptible noise levels. According to the AAMA, a 4 point increase is enough for a perceptible reduction in noise, while a 10 point increase is about 50% lower levels of sound.

Learn more about how our RetroWAL™ interior curtain wall retrofit system can remarkably improve your building’s sound levels – contact Thermolite today.

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The Thermolite engineering staff is an innovative structural, energy modelling, and implementation team that works to create unique window systems alternatives to traditional replacement windows. Our systems protect against blasts, hurricanes, and sound, while being energy efficient and quick and easy to install. We serve a wide range of industry buildings including government, military, historical, schools and universities, financial, health care, hospitality, and offices. Contact us today to learn how we could update your building’s window systems.