Window Acoustics White Paper

Over the years, we have seen a variety of options regarding a widow’s ability to reduce outdoor noise from entering a home or suite. Given the ever-increasing urban densification of our society, expect jurisdictions to introduce demands on a window to minimize this noise. This paper attempts to identify the common thoughts about how a window works and performs acoustically and what conflicts may arise with other codes as a result of this demand.

We’ll summarize the most common options for noise reduction in windows. Some are accurate, and some are not. Let’s start with this list:

1. More glass panes improve performance.
2. Thicker glass and laminated glass perform better.
3. Large air spaces perform better.
4. Offsetting glass thickness in a double-pane window performs better.
5. Sound travels through air leakage.

The items above are general assumptions people make regardless of testing data. Let’s dive into them in turn.

More Glass Panes will Provide Superior Performance

The general idea that more window panes leads to better performance, such as opting for a triple-glazed window as opposed to a double-glazed window, is not entirely true. You may want to consider this when it comes to the cost of a window, plus the added weight that triple glazing brings – they have minimal apparent impact on acoustic performance.

Thicker Glass and Laminated Glass Perform Better

It would make sense that the thicker the glass, the more mass there is to reduce sound transmission. However, mass alone is not the key to a window’s acoustic performance – simply increasing the thickness of a single, double, or even triple-pane window may not provide the desired effect you are looking for. What is key is how the layers of glass are separated. This could be with a soft interlayer in laminate glass which essentially acts as a noise insulator, or through air space, which we will talk about next.

Large Air Space Performs Better

Testing indicates that the separation of glass layers makes a difference to a window’s acoustical performance. So if a larger air space is better, what is the best gap size for a window? We can look to recording studio windows where a 1 to 2” air space is recommended (though it’s worth noting that the larger the gap, the better).

What does this mean for a thermal window? When thermal performance is prioritized, we make the air space about a ½”. This is because a gap of that size is optimal to reduce convection currents in the cavity. As the size increases, the thermal performance of the window decreases.

Offsetting Glass Thickness in a Double Pane Window Performs Better

This is where the magic happens. By offsetting the glass thickness of each pane, such as 3mm and 5mm or 4mm and 6mm in a dual pane window, you create a situation where the vibration frequencies cancel each other out. This will drop the transition of sound through the glazing system and is the single best approach to improving a window’s acoustical performance.

Sound Travels through Air Leakage

As children, we learn that sound requires air and cannot travel in the vacuum of space. As a result, sound will travel through the allowable air leakage in a window frame – bass tones especially. This is why when you sit at a traffic light, all you can hear is the bass from a nearby car and not the full spectrum of music playing. That’s why reducing air leakage in a window is another great way to reduce sound transmission.

There is an assumption that sliding windows leak more air than casement or awning windows, which was true with early edition windows in the 80’s and 90’s. However, as energy codes have improved and the demand for more watertight sliding windows has increased, we are able to get very similar air leakage results. In some cases, with compression gaskets, we can achieve an overall similar OITC rating in a sliding window as you can in casement and awning windows. Below are the air leakage rates from these types of windows for reference. In this case, the sliding window actually has less air infiltration than the casement window, and both pass the A3 rating in the NAFS standard.

Sliding Window Acoustics

Casement/Awning Window Acoustics

Basic Principles when Seeking Acoustically-Rated Windows:

1. Triple-glazed windows will not improve acoustic performance simply by adding panes.
2. Offset glass thickness between panes for both double and triple-pane windows.
3. Do not specify an air cavity greater than ½”, or you may not meet thermal performance expectations in energy codes.
4. Sliders may be just as good as casements based on modern window design.
5. Thicker glass can be used, but balance this with the extra weight on operable sashes and be careful when specifying 6mm triple pane windows.
6. In existing homes, air leakage through walls and other transitions unrelated to the window may result in the whole home’s performance failing to meet expectations. An acoustically upgraded window in an old leaky building may not help.

It’s also worth noting that testing has demonstrated a small but noticeable difference when it comes to frame materials, with vinyl blocking more noise than aluminum. On top of this, it’s important to ensure your windows are installed correctly. Even if you choose a window with superior acoustic performance, if it’s installed poorly, you won’t feel the benefits. That’s why it’s essential to consult the experts.

Reach out to the Window Geeks today to optimize the benefits between acoustic and thermal performance on your project!