Noise Reduction from Secondary Glazing

“Noise” can be defined as a sound that is loud, disturbing or unpleasant. There are plenty of examples of this: heavy traffic, acceleration of vehicles at a junction, motorbikes, buses and lorries, car horns, house alarms, barking dogs, aircraft or noisy neighbours all have the ability to disturb homework, your favourite program, stop a conversation or in particular, wake you or your family up. These things are stressful, and spoil the quiet enjoyment of your property that is often taken for granted.

Many of our customers want to reduce outside noise, and it is natural to start with the windows, as these are often the point at which most noise penetrates. Ironically, older houses with thicker walls are more likely to have windows with single panes of glass and loose unsealed frames, typically (but not always) sash windows. As discussed elsewhere on this site you can replace or refurbish the existing windows, but listed and conservation area properties, being in rental accommodation or financial restrictions may prevent this being feasible – for more details see our costed case study page. Secondary Glazing is an obvious option plus more traditional methods like heavy lined curtains and cork tiles, as well as more extreme solutions like white noise machines, fans or even earplugs. Secondary Glazed windows can be very effective in reducing sound waves, and can be used along with Draught Excluders. Because these products are often inexpensive and quick to fit, they are less disruptive and messy and there are extra bonuses of heat retention for example. 

For heat insulation, a 20mm or so gap between the outer window and a secondary pane is recommended. To reduce noise, the bigger the gap the more air it traps and the better it should perform, although the gap size is often limited by the depth of sill, and the overall design of the windows. In researching this page and preparing our video, we found that opinions on the the best methods of noise insulation vary widely, especially as a lot of information on the subject is written in order to sell specific products, but a general consensus is that Secondary Glazing on a single glazed window insulates better Double Glazing, and similarly Double Glazing with a secondary panel can out-perform Triple Glazing. Whatever method you select, Draught Excluders should also be used on the outer windows.

Easyfix Noise Reduction Experiment

In response to the many enquiries we get at Tubeway regarding improvment in noise insulation from Secondary Glazing, we decided to run an experiment, sharing the results in the video on this page, to illustrate the effectiveness of secondary panels against a common invasive noise. We used a washroom in our factory where a car could be parked directly outside, which meant that the horn, when sounded, drowned out the background noise to give credible results. The car horn also provides a consistent loudness throughout our tests. The window in the washroom is single glazed and tight fitting, so simply closing it makes a big difference. The final test then demonstrates that further reduction in noise is achieved with Secondary Glazing. The resulting video sounds pretty much in the same proportions as it did when being in the room and filming, so we think it is a realistic experiment and trust you will find it useful when considering Secondary Glazing to prevent similar noise issues at your own property.

There is no trick to the timing of the car horn at the right moment – we used an open phone line to our colleague in the car so he could use the script to react at the appropriate times.

The noise meter we used was a Kewtech KEWSL1 Sound Level meter, but as well as the readings provided, the sound track on the video is an accurate indication of the noise improvements at each stage. Taking readings close to the window was deliberate for illustrative purposes and avoided background noise in the building, but be aware that decibel levels diminish when moving away from noisy windows in general.

To give a general idea of common noises and their respective levels, have a look at the diagram below, which gives simple definitions of decibel ranges. Note that to the human ear, a 10 decibel reduction is commonly perceived as reducing the level of noise by half:

diagram illustrating causes of decibel levels

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