While glass looks great aesthetically, it also has to meet high performance standards. An important part of performance relates to acoustics, whether it’s large, dramatic panels used for the exterior of a building, or smaller panels used to create interior partitions. When designing a project there are a number of sound-related factors you need to understand and take into consideration, including:
- The definitions of two ratings: Sound Transmission Class or STC and Outdoor-Indoor Transmission Class or OITC
- The project’s design requirements and how they impact the glazing system, and
- How to calculate an STC or OITC rating
STC versus OITC
The first measure of acoustic performance is referred to as the Sound Transmission Class or STC. This metric measures the sound levels for interior building partitions where the main sounds are people talking or office equipment.
The other measure is known as the Outdoor-Indoor Transmission Class or OITC. This metric measures the sound levels for exterior walls where the sound sources come from the outside, such as cars. This rating is especially important to architects since it can have the largest impact on building performance.
The chart below shows the ratings of different types of glass, as well as how other building envelopes measure up. Quite simply, the higher the rating, the better the product.
|Glass Product Type and Thickness||STC
|¼" Monolithic Glass||31||29|
|½" Monolithic Glass||36||33|
|¼" Glass + ½" Air + ¼" Glass IGU||35||28|
|¼" Glass / 0.030" PVB / ¼" Glass Laminate||38||34|
|1/8" Glass / 0.030" PVB / 1/8" Glass + ½" Air + ¼" Glass IGU||39||31|
|1/8" / 0.030" PVB / 1/8" + ½" Air + 1/8" / 0.030" PVB / 1/8" IGU||42||33|
|½" Gypsum board (both sides) screwed to 3-5/8" metal studs||36|
|6" Lightweight concrete block, two coats of paint each side||46|
|4" Hollow lightweight masonry block, plastered on both sides||48|
|8" Dense concrete block wall, two coats of paint each side||52|
|Double layer of gypsum wall board, both sides, 3-5/8" metal studs, 3" sound attenuation||54|
Consider Acoustic Requirements
Designing with acoustics in mind is just like any other part of the design process, you need to start with the basic system requirements. Some of the first questions to consider are “Where will the sound come from?” “And how much sound is there? These questions are important because the sound reduction properties of materials, including glass, vary depending on the wavelength of the sound occurring around the material.
The following factors are involved in the selection process:
- Determine the glazing system that has the best noise reduction properties.
- When using monolithic glass, increasing the glass thickness can help.
- When using laminated glass, you can increase the glass thickness or use different glass thicknesses for individual glass lites.
- When using insulating glass units, there are several options available, including increasing glass thickness; increasing the air space; evaluating different gas fills, spacers and sealant materials; and using different glass thicknesses for individual glass lites or a laminated component for one or both of the lites.
The other factors that contribute to the overall acoustical properties of a building’s window system include the framing system and the sealants.
After you select the glazing, then you need to determine the STC or OITC rating that the entire system needs to deliver – not just the glass. Keep in mind that the STC and OITC rating numbers equate to how many decibels of noise are reduced by the glazings and that’s why a higher number is better.
As with any project, the building’s envelope system also plays a critical role with glass acoustical performance, making proper installation critical.
For more technical information about glass acoustics, read Vitro Architectural Glass Technical Document TD-135. For any other glass questions, please contact Vitro Architectural Glass (formerly PPG glass) or call 1-855-VTRO-GLS (1-855-887-6457).