However no matter how good the window is at keeping noise out, if it is not installed and sealed properly during construction, noise will still penetrate the home – all air gaps must be sealed off to ensure that a window will achieve the best noise reduction it can.
The Sound Transmission Class (STC) reflects the amount of noise that is reduced when sound passes through the window. So if the noise outside is 70dB and inside it is 40dB, the window is said to have an STC rating of 30. Normally the human ear cannot detect a 1-2dB change in sound. However a 10dB decrease in the sound is subjectively heard by the human ear as a halving of the sound – e.g. a 40dB noise seems half as loud as a 50dB noise. The average spoken conversation makes a 50dB noise, while common street traffic and neighbourhood sounds make about 70dB noise.
Sound waves are what carry noise into a home. To achieve noise reduction you must disrupt the sound waves as they travel through the windows. Using standard glass and window options you will be able to disrupt a sound wave.
- Thicker glass – the further the sound wave has to travel through the density of the glass, the more likely it is to drop some of the sound waves. Thicker glass is often the best solution to reduce low frequency sounds like common traffic and neighbourhood noise.
- Laminated glass – the vinyl interlayer will impact on the sound waves, but as laminated glass usually comprises two panels of equal thickness glass, the sound waves do not have to alter and therefore travel through relatively unscathed. Laminated glass will perform only slightly better than single glazing of equal thickness.
- Insulated glass units – the key to achieving significant sound wave disruption in an IGU is to have as large an air gap as possible (less than 12mm air gap will provide an STC no better than thick glass); and to have the two panels of glass vary in thickness by at least 50% (so a 10mm panel on one side and a 5mm on the other).
- Secondary window – for heavy traffic and aircraft noise a second window with an air space of at least 100mm is the only viable solution to significantly reduce the noise. The use of different thickness glass is recommended, with one of the windows glazed with 10mm glass is ideal.