As I repeatedly discuss in my blog articles, there is no perfect soundproofing or soundproof windows. Windows cannot be made “soundproof”, however, effective window noise reduction treatment is available.
How to measure window noise reduction?
The noise reduction effectiveness of windows is measured by the standardized test procedure ASTM E966 and quantified as Outdoor-Indoor Transmission Class (OITC). OITC is a single number that allows architects and builders to compare the effectiveness of components of the building envelope in reducing outdoor noise. A typical OITC for windows is in the range of 22-26, which is quite low. Windows are typically the acoustically weakest part of a building envelope.
In addition to OITC ratings (or instead), some window manufacturers provide Sound Transmission Class (STC) (specified in ASTM E336-16 and E413-16) ratings because the STC number is higher than the OITC number, and therefore misleadingly appears better, but also because more people are familiar with STC ratings. Typical STC for windows is in the range of 28 to 34. However, the STC rating is intended to quantify the sound attenuation effectiveness of interior partitions, not the building envelope. OITC number provides a more accurate representation of how much outdoor noise will be heard inside through the rated window.
In any case, a higher OITC or STC number means better noise reduction effectiveness; make sure that you are comparing the same classification rating number among different products.
How window noise reduction can be increased?
There are several ways in which sound reduction of windows, or colloquially, soundproof windows, can be archived.
Install better windows
If you are installing new windows, specifying windows with the highest OITC rating makes sense. However, in most cases, replacing existing windows solely for the purpose of increased soundproofing is too expensive and insufficiently effective.
Install noise-reducing curtains
You can reduce noise through windows by installing noise-reducing curtains. These curtains are very heavy and do not admit light. Therefore, they are helpful when you want to reduce noise at night. These curtains can be moderately effective, reducing perceived noise by about 30% to 50% at a reasonable cost.
Install additional interior glazing
Installing an additional glass layer on the interior, some distance away from the existing window is the most effective method of reducing window noise. Spacing between the existing windows and the new glass should be at least one inch, preferably four to six inches [reference 1]. The larger spacing provides more noise attenuation. This solution can reduce perceived noise levels by about 50% to 75%. Most people find this improvement to achieve soundproof windows very significant.
Additional interior glazing is available in two versions:
- Acrylic windows
Plexiglas (acrylic) window glazing, the lower-cost option, is usually installed over special magnetized frames and is held in place by a magnetic strip attached to the edges of the acrylic glazing. This type of additional window is easy to remove for cleaning or ventilation and provides an air-tight seal.
- Laminated glass windows
Laminated glass window glazing is the best and most expensive solution. This window is more aesthetically pleasing than the acrylic in most installations and provides the best sound reduction. The window is made from laminated glass in aluminum frames. It can be made to open to match the existing window for ventilation.
Typical windows, besides being the weakest part of a building envelope from an acoustical standpoint, are also usually the weakest part of a building for heat insulation. Therefore, if you install any of the sound reduction options described here, you also significantly improve the thermal insulation of windows, saving money on heating and cooling bills.
In conclusion, contact The Soundproofing Expert for more information and request a no-obligation quote for consulting or noise-reducing windows in the Toronto area; click on the button below.
 Master Handbook of Acoustics by F.A. Everest and K.C. Pohlmann, Sixth Edition, McGraw Hill 2015, page 363
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