Sound Rated Window Replacement

Why an Ordinary Dual Pane Disappoints You

A standard replacement window has two sheets of glass, usually both about an eighth of an inch, separated by a narrow sealed cavity. That is a good arrangement for heat and a poor one for noise, and the reason is symmetry.

Identical panes have an identical resonant frequency. Sound arriving at the outer pane sets it vibrating, and because the inner pane wants to vibrate at exactly the same rate, it takes that motion up willingly and re radiates it into the room. The window behaves less like a barrier and more like a drum skin with a second skin behind it. Worse, that shared resonance in a typical residential unit falls in the low range, which is precisely where freeway noise lives. Tyres on concrete, a diesel pulling the grade, an engine brake at two in the morning.

That is the mismatch we see over and over on the streets near the 91. Somebody spent real money on new windows, the house got warmer in winter and cooler in August, and the traffic sounds much the same as it did before.

What We Change

Three things, in order of how much they matter.

Unequal glass thicknesses. Making the outer pane meaningfully thicker than the inner one, or the other way round, means the two sheets no longer resonate in step. One damps the other. This is close to free, it is simply a different unit ordered from the same supplier, and it is the first thing to specify.

A laminated pane. Laminated glass is two thin sheets bonded to a plastic interlayer. That interlayer is viscoelastic, which is a technical way of saying it converts vibration into a very small amount of heat instead of passing it along. It is the largest single improvement available in a residential window, and it brings two useful side effects: it blocks essentially all ultraviolet, so furniture and flooring on a west facing wall stop fading, and it holds together when broken.

The widest cavity the frame will take. Air gap does real work at low frequencies. A wider gap decouples the panes further. Frame depth limits how far you can go, which is one of several reasons a retrofit into a shallow old frame has a ceiling on it.

Reading the Numbers Honestly

You will be quoted an STC figure, Sound Transmission Class. It is a single number condensed from performance across a band of test frequencies, and it is genuinely useful for comparing units. A plain dual pane usually sits in the high twenties. A properly specified sound package reaches the mid thirties.

The caveat matters here. The STC test weights speech frequencies heavily, because it was designed for office partitions and party walls. Freeway noise is much lower pitched than speech. Two windows carrying the same STC number can perform noticeably differently against a truck on the 91, and the one with the laminated pane and the wider gap will be the better of them nearly every time. If a supplier can show you performance by frequency band rather than a single figure, that is the sheet worth reading.

What It Will Not Do

It will not make the freeway inaudible, and we say that on every visit. A house is a system, and glass is one part of it. If the front door is a hollow slab, or there is an unsealed attic vent facing the road, or the wall itself is thin, the window can only take you as far as the next weakest path.

What a well specified window does is move ordinary traffic from something you notice to something you have to listen for. Sleep gets easier. Television volume comes down. In our experience that is the change people actually wanted when they called about noise, and it is achievable.

Call (951) 407-5252 and tell us which rooms are the problem.