How many dB does secondary glazing reduce?

Properly installed secondary glazing reduces external noise by 45-54 dB depending on glass thickness, air gap, and seal quality. For context: a 10 dB reduction halves perceived loudness. A 45 dB reduction takes 80 dB of traffic noise (loud lorry) down to 35 dB (library quiet).

Is secondary glazing better than triple glazing for noise?

Yes, significantly. Triple glazing reduces noise by 35-40 dB at best because the panes are close together. Secondary glazing with a 150-200mm air gap achieves 48-54 dB because the wide air gap dramatically reduces sound transmission. Acoustic engineers always recommend secondary glazing for serious noise problems.

Will secondary glazing block aircraft noise from Heathrow?

Yes. With 10mm acoustic laminated glass and a 150mm+ air gap, secondary glazing can reduce Heathrow approach noise by 50+ dB — bringing 90 dB jet noise down to 40 dB (whisper level inside). This is why most properties under the Heathrow noise mitigation scheme received secondary glazing rather than replacement windows.

What's the minimum air gap for noise reduction?

100mm is the minimum for meaningful acoustic performance. Below 80mm, secondary glazing performs similarly to standard double glazing. For traffic noise, target 100-150mm. For aircraft or rail noise, aim for 200mm+ where the existing reveal allows.

Do you need acoustic glass or is standard enough?

It depends on the noise frequency. Standard 4mm glass with a 150mm air gap handles most road traffic noise well. For low-frequency noise (HGVs, helicopters, bass-heavy music venues), upgrade to 6.4mm or 10mm acoustic laminated glass — the PVB interlayer absorbs low frequencies that standard glass passes through.

How to Reduce Noise from Traffic & Aircraft

Updated 8 June 2026 · 7 min read

A calm bedroom with acoustic secondary glazing beside a busy road

If you've tried curtains, draught strips and double glazing and you can still hear the road — secondary glazing is the upgrade that actually works. Here's how to specify it correctly.

Why standard double glazing doesn't stop traffic noise

Most homeowners assume double glazing solves noise — it doesn't. Standard A-rated double glazing reduces external noise by 28–32 dB. That's because the two panes are bonded together with a 16–20mm spacer bar, which transmits sound vibrations directly from outer pane to inner pane.

Secondary glazing achieves 45–54 dB reduction because the inner pane is mounted in a completely separate frame with a 100–200mm air gap. Sound waves lose energy crossing that gap and have nothing to vibrate through.

The dB reduction table

Real-world noise reduction figures for different secondary glazing configurations:

Configuration	Air gap	Glass	dB reduction
Single + secondary (slim)	80mm	4mm float	38 dB
Single + secondary (standard)	100mm	4mm float	42 dB
Single + secondary (deep)	150mm	6mm toughened	48 dB
Acoustic spec (recommended)	150mm	6.4mm acoustic laminated	51 dB
Heavy acoustic spec	200mm	10mm acoustic laminated	54 dB

What 50 dB actually sounds like

Decibel reductions are logarithmic, which makes them hard to visualise. Here's what real noise sources sound like after secondary glazing treatment:

Noise source	Outside (dB)	Inside after 50 dB reduction
Suburban traffic	65 dB	15 dB (silence)
Main A-road	75 dB	25 dB (whisper)
HGV passing	85 dB	35 dB (library)
Heathrow approach	90 dB	40 dB (quiet office)
Pub closing time	70 dB	20 dB (rural night)

Specification by noise problem

Suburban road noise

For typical residential streets with intermittent traffic, a 100mm air gap with 4mm or 6mm glass is sufficient. Expect a 40–44 dB reduction and a transformed sleeping environment. Typical cost: £550–£700 per window.

Main road / A-road

Continuous traffic noise needs a deeper air gap. Target 150mm with 6mm toughened glass or 6.4mm acoustic laminated. Expect 48–51 dB reduction. Typical cost: £700–£850 per window.

Flight path (Heathrow, City, Stansted)

Aircraft noise is predominantly low frequency, which standard glass transmits efficiently. Specify 10mm acoustic laminated glass with the deepest possible air gap (180–200mm where the reveal allows). Expect 52–54 dB reduction. Typical cost: £850–£950 per window.

Pub, club or entertainment venue nearby

Bass and music noise is the hardest to block. Use 6.4mm or 10mm acoustic laminated glass (the PVB interlayer is critical here), a 150mm+ air gap, and ensure the perimeter seals are premium-grade compression seals not standard brush seals. Typical cost: £800–£950 per window.

Rail noise

Rail noise is mixed frequency with sharp peaks during train passes. The same spec as flight path treatment works well: 10mm acoustic laminated, 200mm air gap. For properties within 50m of the track, also consider isolation mounts on the subframe to prevent structural vibration transfer.

Why the seals matter as much as the glass

A common installation failure: premium glass paired with cheap brush seals. Brush seals leak high-frequency noise around the perimeter, undoing the acoustic performance of the glass. Specify compression seals or premium EPDM gaskets. We use Wakefield/Q-Lon perimeter seals on all acoustic installations.

Real Presswarm installations

Recent acoustic projects we've completed:

Hounslow, TW3 — Heathrow approach path.4-bed semi, 10 windows. 10mm acoustic laminated, 180mm air gap. Customer reported "completely transformed" sleep quality. Cost: £8,400.
Hackney, E8 — main road frontage. Victorian terrace, 6 front-facing sash windows. Vertical sliding secondary with 6.4mm acoustic glass. Cost: £4,950.
Hertford town centre — pub noise. Apartment above a bar. 4 windows, 10mm acoustic, 200mm air gap. Reduced 95 dB closing-time noise to inaudible. Cost: £3,600.

Get a free acoustic assessment

We'll measure your existing noise problem with a calibrated dB meter and specify the exact glass and air gap you need. No commission, no upselling.

Get a free quote Call 01992 636400