Double Glazed Windows and Doors Pty LtdAcoustic Windows using Windowfactory Upvc Double Glazed Windows Article
Double Glazed Windows and Doors Pty Ltd

This article by can assist consumers who are looking at double glazing for noise insulation, and more specifically, acoustic upvc double glazed windows.

Our world has become a loud place. Noise is one of the greatest environmental problems of our time – not only for those living near airports, railway tracks, or arterial roads. Windows that provided adequate protection decades ago are now a danger to our health because they cannot stop noise.

Many consumers already know that the primary determinants of acoustic performance in a window are: glass thickness, air-gap and acoustic sealing. The requirements for windows are particularly high, with our partners Kommerling, we consistently achieve above and beyond the results specified in acoustic engineer reports - making many customers comfortable and happy. Together, and Kommerling, offer their insights to all our customers about improving acoustic insulation of windows.

A window element consists of
• glass pane
• frame
• hardware

• connection to the building

All of these have an effect on the sound insulation of the whole element.

The following measures are basic options for raising the sound insulation of windows:

1) increasing the pane thickness

2) increasing air-gap
3) Asymmetrical multiple glazing
4) using laminated glass
5) selecting appropriate window type: improving pane size and geometry

6) thorough joint layout / installation
7) using structurally robust frame material
8) using heavy gas filling

Some methods are more effective than others. Adding a heavy glass filling improves results only marginally, whereas increasing the air-gap and glass thickness improve acoustic insulation dramatically! There is a positive relationship between glass thickness and cost ie thick laminated glass is more expensive than thin float glass, but the air-gap is still free - so choosing a system with the biggest air-gap can increase performance and add value.

The thickness of the pane has a great effect on its insulation properties: the greater the weight per unit area, the higher the sound reduction index. A glass pane 4 mm thick exhibits theoretically a sound reduction index Rw of 30 dB, a pane 10 mm thick an index Rw of 35 dB. However, the installed pane is an oscillatory system and there may be intrinsic vibration under certain stimuli and sound incidence angles that could lead to a clear loss of sound insulation (coincidence effect). Assymetrical glazing can counteract the drawbacks of the coincidence effect and lead to considerably higher sound insulation for the window. With a 4/16/4 layout the resonance lies in the particularly sensitive range between 1 and 3 kHz. Above this resonance frequency a multiple glazing design exhibits a higher sound reduction index than a single glazing design with the same pane thickness. On average a multiple glazing design leads to an improvement of 3 dB. With an asymmetrical layout, e.g. 6/16/4, the differing intrinsic frequencies suppress resonance for even greater improvement.

Frame materials for windows are (virtually exclusively) aluminium, wood and upvc. Up to medium sound transmission class, the frame material itself has a subordinate role where acoustics is concerned, but there are differences in the static properties, thermal insulation, durability, and care requirements. Aluminium is a good conductor of heat (bad thermal insulator). Wooden frames require quite a bit of maintenance. Upvc frames, on the other hand, exhibit adequate static properties when reinforced, are good heat insulators, and are easy care. With windows of high sound transmission, the design of the frame is important. Here, particular importance must be attached to joint tightness and high weight per unit area. Frames of light wood are a drawback in this case. The sound reduction index of wooden frames is about 37–39 dB, that of upvc frames approx 41 dB.

The joint layout and how the element is installed in the building substrate are particularly important for the sound insulation of the whole window element. This is affected by the joint’s geometry, its shape and surface, and the acoustic properties of the joint fasteners and filler. Narrow open joints particularly reduce insulation at higher frequencies. The following designs are particularly beneficial to sound insulation.

offset joints v smooth joints: sound deflected in offset joints loses energy

joints backfilled with materials of high flow resistance: sound energy in flow resistant materials is converted to heat

joints sealed with materials with a low modulus of elasticity: a high modulus of elasticity promotes the transmission of structure borne noise and so reduces sound insulation

high compression sealing

The tightness of the window is decisive for good insulation values. With casement, awning and tilt & turn styles you have the assurance that your windows are permanently tight – between sash and frame, pane and sash, and at the connection to the building. In general, most sliding windows under-perform any other window type because of a lack of acoustic sealing - they do not have the same level of tight interaction between frame and sash, because they are ordinarily made with thin mohair brushes. However, sliding windows as secondary double glazed windows have been used effectively. The key factor with secondary double glazed windows is maximizing the air-gap, this is the most important contributor to their effectiveness.

The opened window lets outside noise into the room, e.g. about 75 dB for heavy traffic.
An old, often loose fitting, single glazed window absorbs only about 20 dB, completely inadequate for today’s
noise pollution levels.
Our Casement, Awning and Tilt&Turn windows with standard insulating glazing achieve 32 dB and reduce noise to a tenth.
Our Casement, Awning and Tilt&Turn windows with active insulating glazing achieve 45 dB, i.e. noise reduced to a twenty fourth.

Word limit on this site requires an abrupt end to this article, but we hope the above information is useful. For expert advice and a quote for your acoustic windows, contact our team by email or check back soon for the next installment of the article.

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