Soundproofing a double glazed window

24 Feb 2008
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United Kingdom
Will the installation of secondary glazing on an already double glazed window, significantly make a difference sound proof wise?

I've looked all over the internet for soundproofing and if you've got single glazed windows and are adding secondary then there's lot of info and technical data about noise reduction but not with regard to installing secondary as an add on to double glazing.

Any ideas?! Thanks in advance for any help with this.
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Double glazing is supposed to reduce noise to an acceptable level. Therefore secondary glazing is unlikely to be needed. So there is little need for data on how effective secondary glazing will be in reducing the noise that has got through the double glazing.

The best reduction of sound through two layers of glass is when the second layer of glass is a different thickness or type than the first. Double glazing where one sheet is 4 mm thick and the other is 6 mm thick reduces sound far more than if both sheets are the same thickness. If they are in the same solid frame then sound vibration will pass from outer sheet t oinner sheet via the frame

The secondary glazing in my cottage is very effective at reducing sound. The window are wooden with 6 or 8 panes per window of mainly spun glass. The secondary glazing is about 3 inches in from the windows and single sheet. The frame of the secondary is not attached to the window frame but instead to the wall, hence there is no path for sound vibrations from frame to frame
Secondary glazing fitted with a 100mm air gap between the window is ment to be one of the best way to reduce noise.
Different thickness's of glass will make a little difference but not much, Specially made acoustic double glazed units (which are ridiculously expensive) will only lower decibel levels by around 30DB, This is equivalent to someone whispering or leaves rustling in a tree.

But before you go through that expense:
Are you current windows PVC and do they have PVC trims all around them? If so you may want to peel up one of the trims and see if the windows have foam around them or just a big void.
Are the sash's closing properly? Give your hinges a clean, A spray with Silicone spray and put a little grease in the corner tabs of the hinges.
Do you have trickle vents? These can let alot of noise in.
It's done to homes around airports, and it does make a significant difference. The air gap available in the reveal is important - typically a 4mm float glass with 150mm air gap or 6mm with a 100mm gap. Or there is specialist laminated glass available which is even better.

Sound reduction of around 50db is often quoted, but I don't know what that means in context.
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As Woody says , if you can get an airgap of 150mm between existing panes and the new seconsary glazing, you willsee the best returns in reduction of noise wise ( Source at Granada Secondary Glazing...)
As has been alluded to , you can also get Laminate glass that has a special interlayer , instead of the standard , which is designed to reduce noise....typically a product called ' Stadip Silence ' ( produced by Saint Gobain/Solaglas ). We have provided this glass in a 12mm format , for a studio before now
Thankyou for all your replies - all REALLY helpful. I should have mentioned that the thinking behind getting secondary glazing is that I want to turn part of my office into a sound booth. I don't have the resources to build a fully soundproofed booth (or the floor to take the weight) and I know that it's never going to be fully soundproofed but I just want to reduce any ambient noise as much as possible. Will definitely check out the different types of glass and look under the plastic strips that surround my window. All good stuff.

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