Soundproofing Windows with Secondary GlazingUp to 80% Quieter with Acoustic Glass

Soundproofing Windows vs Acoustic Windows

No window is fully soundproof, but you can get very close. "Acoustic windows" usually means replacement double glazing with laminated glass, where the two panes sit only 12–20mm apart. That narrow gap limits how much noise it can stop, typically 32–38dB.

Soundproofing windows with secondary glazing works differently. A separate inner window sits 100–200mm behind your existing one, and that wide air gap decouples the two panes. With acoustic laminate glass and good seals, the combined window can reach up to 54dB, which is why it is the go-to choice for flats on main roads, homes under flight paths and listed buildings where the original windows must stay.

The Right Specification for Your Noise

Different noise sources need different solutions. Low-frequency rumble from trains behaves very differently to the broadband roar of aircraft, so we match the air gap and glass to your specific problem. Here is how we approach the most common sources:

How Acoustic Secondary Glazing Works

• The air gap does the heavy lifting. A 100–200mm gap decouples the panes so vibration can't pass straight through — far wider than double glazing's 16–20mm.
• Acoustic laminate glass. A PVB interlayer absorbs sound energy — read why 10.8mm acoustic laminate is the gold standard, or compare options in our guide to acoustic glass thickness.
• Airtight seals. Noise leaks through gaps, so high-performance compression seals are essential. See our complete soundproofing guide.
• Specific noise problems. We have detailed guidance on Heathrow flight-path noise and Tube and Underground vibration.

What the Decibel Numbers Really Mean

Noise reduction is measured in decibels (dB), but the scale is not linear — it is logarithmic. A reduction of just 10dB is perceived by the human ear as roughly halving the loudness. A single-glazed window typically blocks only around 25dB, which is why traffic feels like it is in the room. A well-designed acoustic secondary glazing system with 10.8mm acoustic laminate glass and a wide air gap can achieve up to 54dB of reduction.

In practice that is the difference between a busy A-road being intrusive and being a faint background hush. For homes beside railways, flight paths or nightlife, that extra 20–30dB over the original window is genuinely life-changing for sleep and concentration. For a deeper look at how noise reduction is measured and specified, see this independent resource on secondary glazing noise reduction.

Glass Options and Why Secondary Beats Double Glazing

The glass specification is chosen to match your noise problem and budget:

• 4mm toughened. A solid entry point that transforms a leaky single-glazed window and prioritises thermal gains.
• 6mm toughened. Extra mass adds a few more decibels — the value “sweet spot” for quieter residential streets.
• 6.4mm and 10.8mm acoustic laminate. A specialist PVB interlayer damps the vibration that ordinary glass lets through — the gold standard for A-roads, railways and flight paths.

This is also why secondary glazing outperforms replacement double glazing for sound. Double glazing's two panes sit only 16–20mm apart and are rigidly sealed together, so they vibrate almost as one. Secondary glazing places a completely independent pane 100–200mm away from the original, and that wide, decoupled air gap is the single most important factor in stopping low-frequency noise. Every system is bespoke-made, professionally installed, and starts with a free acoustic survey.

Where It Makes the Biggest Difference

You do not have to treat every window in the house at once. Most clients start with the rooms where noise costs them the most: street-facing bedrooms, nurseries where a passing siren undoes an hour of settling, and home offices where concentration matters. Treating two or three key rooms first is a perfectly sensible way to spread the investment, and because each unit is made to measure you can extend the system later without anything looking mismatched. The same acoustic systems work in classrooms, hotel bedrooms and meeting rooms, and our commercial secondary glazing service fits them out of hours so the building stays open.

We are also honest about expectations. No window delivers absolute silence, and anyone promising it is overselling. What acoustic secondary glazing reliably does is remove the intrusive edge — the individual bus, the shout at closing time, the 6am delivery — so the remaining sound sits below the threshold that wakes you or breaks your focus.

Compare options in our secondary glazing vs double glazing guide, see costs, or return to our complete guide to secondary glazing. We install noise-reducing secondary glazing across London and every borough we serve.

Noise Reduction Windows: FAQs

Common questions about acoustic secondary glazing and how much noise it removes.