A wall or window is typically rated in either sound transmission class (STC), apparent sound transmission class (ASTC), or by the outdoor-indoor transmission class (OITC). The higher the number the better. Even though OITC is a better indicator of noise reduction at lower frequencies (such as highways, train tracks or airports), the STC rating is much more commonly used. Recommended STC ratings for meeting rooms and offices are 45 to 50, however a common STC rating for a standard double-glazed window is only between 28 and 32.
This has given rise to the increased use of laminated glass for increased sound comfort. Bonding two pieces of glass together with a thin plastic interlayer has proven to increase the STC rating of glass by around four. Two laminates can increase the original STC rating by around eight. Even still, until the STC rating is above 40, building occupants will often complain about exterior noise.
According to the NRC’s published data, in order to exceed STC 40 you need one of the following configuration options:
- Double glazing with glass four millimeters thick and an interpane spacing of 100 millimeters
- Double glazing with glass six millimeters thick and an interpane spacing of 90 millimeters
- Triple glazing with glass three millimeters thick and interpane spaces of six and 100 millimeters
So why were a couple people talking about this with me on the trade show floors? It was because both the contractor and supplier wanted to go above and beyond on specific projects they were working on. Our building codes are not pushing us to improve STC ratings and rarely will clients pay the premium cost to increase to triple-glazed or laminated windows when double-glazed will do. But as the push continues for lower U-value window systems, one of the side benefits will be improved STC ratings. And that sounds good to me.•