Does Secondary Glazing Reduce Noise?
Noise is the single most common reason people buy secondary glazing, and it is the application where it genuinely outperforms replacement double glazing. The size of the improvement depends on three things you control and one you do not.
The three things that decide the result
First, cavity depth. The distance between the existing glass and the new pane is the biggest single factor, and anything from 100mm upwards works properly. Second, glass mass and damping. Acoustic laminated glass has a soft interlayer that stops the pane ringing, and it should be a different thickness to the original glass so their weak points do not line up. Third, the perimeter seal. A tiny continuous gap around a frame will undo an expensive glass specification, which is why made to measure and templated fitting matters.
- Cavity depth is the biggest single factor
- Mismatch the two glass thicknesses deliberately
- Acoustic laminated adds damping, not just weight
- A leaking seal wastes the glass spend
The thing you do not control
The rest of the building. Once the window is treated, the next weakest path takes over, whether that is a letterbox, a lightweight door, an air brick, an extract vent, a suspended timber floor or a party wall. This is why the honest answer to how much quieter a room will be is always specific to that room rather than a headline number, and why we would rather look at your particular window before promising anything.
Why it beats double glazing on noise
A sealed double glazed unit has a narrow cavity, and the two panes are effectively coupled through it, so at certain frequencies the unit behaves almost like a single heavier pane. A secondary glazing cavity of 100mm or more decouples the panes, which is why acoustic consultants specify secondary glazing on noise sensitive projects and planning conditions rather than replacement windows.
What it feels like in the room
People rarely describe the change in decibels. They describe traffic becoming a distant hum instead of individual vehicles, being able to sleep with a train line at the end of the garden, no longer hearing conversations from the pavement, and the television going down a couple of notches. The peaks soften first, and the peaks are what wake you.
Frequently asked questions
The honest answer depends on your cavity depth, glass, seal quality and what the rest of the wall is doing. We will assess your window rather than quote a headline figure that may not apply.
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South Yorkshire's specialists in secondary glazing — survey, measure, manufacture and install.