Soundproof secondary glazing

If traffic, trains or street noise is keeping you awake, secondary glazing is usually the most effective glazing upgrade you can make. Here is why the air gap matters, how much difference it makes, and what to expect.

Why secondary glazing beats standard units for noise

It sounds counter-intuitive, but for sound insulation the gap between panes matters more than the number of panes. A sealed double-glazed unit has a narrow cavity (typically 16–20mm) optimised for heat, not sound. Secondary glazing lets you set the inner pane 100mm or more from the existing window, and that large air gap is far better at absorbing low-frequency noise like rumbling traffic. A thicker or laminated acoustic pane improves it further. For the wider context of glazing choices, see types of glazing explained.

How much quieter will it be?

Noise reduction is measured in decibels, and results depend on your existing window, the gap and the glass. A well-specified secondary glazing installation can make a noticeable, sometimes dramatic difference to perceived noise — a busy road can drop to a background hum. Because every home is different, treat any specific figure as a typical range rather than a guarantee. An installer can advise on the right pane and gap for your situation.

Getting the specification right

Three things drive the acoustic result:

• The air gap — bigger is better for sound; 100–200mm is common for acoustic jobs.
• The glass — a thicker pane, or laminated acoustic glass with a special interlayer, dampens more sound. Our toughened vs laminated glass guide explains the laminated option.
• The seals — brush or compression seals stop noise leaking around the edges.

Keeping it sympathetic

Because secondary glazing sits inside and leaves the original window alone, it is ideal for flats and period homes — including listed buildings — where you cannot change the external appearance. It is the same reason it is a popular, reversible upgrade covered on our secondary glazing quotes page. Good seals and glass are part of the glazing tech that cuts heat loss as well as noise.

Getting a quote

A surveyor will measure the reveal, recommend a gap and pane, and confirm a written price at a free home survey with no obligation. If you are weighing a full window swap instead, compare replacement quotes by window type; if you want to understand the underlying issue first, see which window problems glazing solves; and if you are ready to move, here is getting new windows sorted quickly.