Acoustic Efficiency - Please select from the headers below:

The Acoustic Efficiency of windows refers to the ability of a closed or fixed window to reduce external noise entering your residence.

Key Issues and Considerations:

When designing or modifying a window the work must comply with the Building Code of Australia and consideration should be given to the desired reduction of outside noise. Construction that reduces the ingress of external noise must be designed to ensure that it is integral with all other Building Rules requirements such as energy efficiency.  Windows will provide an acoustic weakness to the external facade of a building as noise is generally transferred more easily through glazing than through the external walls. Improving the sound insulation of windows will help to reduce external noise ingress. The larger the glazed area, the greater the sound transmission through the window, so the level of noise reduction will be dependent on the area of glazing that is treated. The noise transfer through and around windows can be reduced by using thicker and/or laminated glazing, a double glazed system and high quality window perimeter seals.

The ability of a window to reduce noise is dependent on the following elements:

  • Frame Design
  • Glazing
  • Composition of glass types
  • Distance between glasses
  • Seals


The Acoustic Efficiency of windows refers to the ability of a closed or fixed window to reduce external noise entering your residence.


There are several different materials commonly used for window frames, however, the type of material does not usually have a significant influence on noise reduction properties. The effect of perimeter window seals are the critical issue in window frames. The window should be well sealed between the frame and the supporting wall as sound can flank around the window when not properly sealed. This also improves thermal efficiency and prevents moisture ingress. The selection of window type can improve acoustic performance as awning windows with outward opening sashes are preferred to sliding windows as when closed they achieve a positive compression seal against the window frame. There are also proprietary framing systems that provide improved acoustic performance.


There are 2 main glazing construction options available:

  • Single glazing -  is the use of a single pane of glass in a window.
  • Double glazing - is the use of two panes of glass in a window separated with a spacer.


For single glazed windows, after appropriate sealing the thickness of glass is the major factor influencing the passage of sound. Typically, thicker glass offers better sound insulation than thinner glass, particularly when the major problem is low frequency noise such as truck engine or music noise. Toughened, coated, wired and patterned glass types behave acoustically similar to standard float glass.

Laminated glass performs slightly better than other types of glass when the major problem is high frequency noise such as tram wheel squeals or traffic noise. The improvement is due to a PVB (polyvinyl butyral) interlayer that helps to reduce the passage of sound at high frequencies. This layer is sandwiched between two panes of glass. However, laminated glass offers little improvement over other glass of the same thickness when the main problem is low frequency noise.

Laminated glass can also offer a thermal protection layer that can significantly improve energy efficiency. Thick PVB laminated glass in conjunction with tight seals and a well manufactured and installed frame system ensures a good level of sound insulation.

Air or Gas Filled

Insulating double glazed systems with a gas other than air (usually an inert gas such as argon or krypton) in the airspace between panes is another recent innovation in window technology.

Gas filling increases thermal insulation but does not significantly contribute to noise reduction.

Distance between Glass Panes in Secondary Glazing Systems...

In most cases, the larger the air cavity between glass panes in double glazed systems, the more noise the window system can reduce. All air gaps must be sealed to ensure the window achieves maximum noise reduction. Small air gaps between panes of glass can provide good thermal insulation properties but only offer minimal acoustic insulation.


As with all building structures, cracks enable sound to enter a building. These noise flanking paths can defeat noise reduction techniques. This is of particular concern for windows that open. Even windows with good weather stripping can have compromised noise reduction due to air leakage.

Windows should have perimeter acoustic seals to reduce flanking. With fixed glazing, the noise transfer via flanking paths around the pane should be minimised with high quality perimeter seals - for windows that open the perimeter seals do not work as well. For openable windows, awning windows are more effective over sliding or pivoting windows as they are able to achieve a positive compression seal.

*Note: acoustic seals only provide suitable performance if they are properly fitted.

Seals should be selected on their performance and simplicity of use, and they should be low maintenance and have a long life. Solid seals are more effective acoustically than brush type seals in sealing any gaps around the window perimeter airtight. Correct installation is an important aspect of window treatment.


Distance between Glass Panes in Secondary Glazing Systems...

The following provides examples of different acoustic treatments for windows. They are provided as examples only and are by no means exhaustive. Consultation with an acoustic consultant to ensure correct design for your project is recommended.

Rw is the Weighted Sound Reduction Index which is a measure of the sound insulation performance of a single building element (such as walls, windows etc.).

The higher the Rw rating, the better the sound insulation.

Single Glazing

  • Single glazing in non-sealed frame: (Rw 15 – 20)
  • 6mm float glass set in a non-sealed timber frame.
  • Single glazing with acoustic seals: (Rw 30 – 33)
  • 6mm or 10mm glass set in sealed metal or timber frame.
  • Single laminated glazing with acoustic seals: (Rw 33 – 36)
  • 6.38mm or 10.38mm PVB laminated glass set in sealed metal or timber frame.

Double Glazing

  • Double Glazing: (Rw 40 – 45)
  • 6mm glazing – 10 to 50mm air gap – 6 mm glazing set in a sealed metal or timber frame.