How much traffic noise can secondary glazing block?

Up to 54dB total system performance with 10.8mm acoustic laminate at a 150-200mm cavity. In practice a bedroom at 60dB typically falls to around 32dB, below the WHO 35dB night-time guideline.

Why does bus and lorry noise need a deeper cavity?

Heavy vehicles produce a 60-125Hz component that mass alone does not stop. Low frequencies require mass-spring-mass decoupling, which comes from cavity depth — a 50-75mm gap loses 6-8dB against a 150-200mm gap in that band.

Is acoustic laminate really better than thicker plain glass?

Yes. Plain glass has a coincidence dip that sits inside the traffic band, so it re-radiates sound. The damping PVB interlayer in acoustic laminate suppresses that dip and is worth 4-5dB exactly where road noise concentrates.

Do I need a sound survey before ordering?

We recommend one and provide it free. Measuring the actual facade and internal dB levels and the frequency profile determines whether 6.4mm or 10.8mm laminate and what cavity depth your specification needs.

Secondary Glazing for Traffic Noise

Engineered for the 100-1000Hz band where road noise actually lives.

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70-78dB

Typical A-road facade level

54dB

Achievable reduction

100-1000Hz

Dominant traffic band

35dB

WHO night-time guideline

Road traffic is London's dominant noise source and the reason most of our surveys are booked. A busy A-road produces 70-78dB at the facade, with energy concentrated between 100Hz and 1000Hz — tyre roar, engine load and the low-frequency rumble of buses and HGVs.

That frequency profile is what the specification has to answer. Standard 4mm glass has a coincidence dip right in the middle of it. Acoustic laminate with a damping PVB interlayer removes that dip, and a deep decoupling cavity handles the low end.

What traffic noise is made of

Below 30mph, engine and exhaust noise dominates and sits low in the spectrum. Above 30mph, tyre-road interaction takes over and moves energy up into the 500-1500Hz range. Buses and HGVs add a 60-125Hz component that travels furthest and is hardest to stop, which is why living on a bus route feels different from living on a car-only street.

Cars at speed: 500-1500Hz tyre roar
Buses and HGVs: 60-125Hz structural rumble
Braking and acceleration at junctions: broadband peaks
Wet road surfaces: +3-5dB across the band

The specification that works on main roads

For an A-road or bus route we specify 10.8mm acoustic laminate at a 150-200mm cavity. The laminate mass handles the mid band, the acoustic PVB damps the coincidence dip, and the deep cavity provides the mass-spring-mass decoupling that low-frequency bus rumble requires.

A shallower 50-75mm cavity — common in cheaper installations — costs you 6-8dB precisely in the low band where the problem is worst.

What the result feels like

A 25-30dB reduction takes a 60dB bedroom to around 32dB, which is below the WHO 35dB night-time guideline. Perceptually, a 10dB reduction is heard as roughly half as loud, so 27dB is heard as a fall to well under a quarter of the original intrusion.

Traffic noise specification

Glass: 10.8mm acoustic laminate with damping PVB interlayer
Cavity: 150-200mm for low-frequency bus and HGV rumble
Seals: Full-perimeter EPDM compression
Target band: 100-1000Hz, with low-end extension to 60Hz
System performance: Up to 54dB
Typical result: 60dB bedroom reduced to ~32dB

Pricing guide

Specification	Price	Notes
Main-road bedroom window, 10.8mm	from £620	150mm cavity specification
Standard road frontage, 6.4mm	from £480	Quieter residential streets
Front elevation package (4 windows)	from £2,280	10.8mm throughout
Free acoustic sound survey	Free	dB measurement before specification

All prices supplied and fitted in London, inclusive of survey and 25-year warranty. See the full secondary glazing price list.

Case study: Bus route bedroom in Hammersmith

Hammersmith, W6

Problem: 76dB peaks from a 24-hour bus corridor; 61dB at the bed head with 45+ vehicle events per hour overnight.

Solution: 10.8mm acoustic laminate sliders at a 180mm cavity across two front bedroom windows.

Result: 29dB reduction to 32dB internally — below the WHO night guideline, with bus rumble no longer audible.

Frequently asked questions

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