Acoustic Window Inserts & Sound Insulation
Purpose-engineered secondary glazing inserts that turn a single-glazed London window into a laboratory-verified 54 dB Rw acoustic barrier — without touching the primary window or requiring planning consent.
The physics: mass, air, mass
Sound transmission through a window is governed by three variables: the mass of each glass leaf, the depth of the air cavity between them, and the mechanical decoupling of the two systems. Sealed IGUs are limited to a 6–20mm cavity — insufficient to decouple below 500 Hz — which is why replacement double glazing rarely resolves traffic-noise complaints. Acoustic window inserts break this ceiling by placing a second glazing plane 100–200mm behind the primary, forming a resonant cavity tuned below the audible speech range.
Glass specifications we specify for sound insulation
| Glass build | Weight | Rw (single leaf) | Best use |
|---|---|---|---|
| 4mm float | 10 kg/m² | 29 dB | Baseline thermal upgrade |
| 6.4mm laminated | 16 kg/m² | 33 dB | Urban traffic (secondary A-road) |
| 6.8mm Stadip Silence | 17 kg/m² | 37 dB | Primary A-road, mainline rail |
| 10.8mm Stadip Silence | 27 kg/m² | 40 dB | Flight path, elevated rail |
| 12.8mm Stadip Silence | 32 kg/m² | 42 dB | Extreme (recording studio) |
Combined with the primary window's existing 3–4mm float pane and a 150mm cavity, these builds deliver system-level Rw values of 40–54 dB — verified by BRE hot-box testing to BS EN ISO 10140-2.
Frame acoustics — decoupling matters
A 54 dB glass build fitted into a poorly sealed frame will deliver only 35–38 dB in situ. We specify:
- Twin EPDM compression seals to primary and secondary frame perimeters.
- Neoprene isolation gaskets between sub-frame and reveal — decouples structure-borne flanking transmission.
- Acoustic mineral wool cavity absorber (30 mm) around the reveal perimeter, unseen from the room.
- Butt-jointed corners with silicone acoustic sealant, not mitred foam gaskets.
Verification: field measurement
On completion we can arrange a UKAS-accredited third-party field test to BS EN ISO 16283-3 (façade sound insulation), producing a D2m,nT,w value directly comparable to Building Regulations Approved Document E and BB93 (schools). Typical London acoustic-glazing projects achieve D2m,nT,w ≥ 43 dB — sufficient to bring a bedroom overlooking the A40 within WHO night-noise guidelines.
Common noise sources and target Rw
- Suburban street traffic (55 dB LAeq): target Rw ≥ 38 dB — 4mm secondary sufficient.
- Primary A-road (65–70 dB LAeq): target Rw ≥ 45 dB — 6.8mm laminate at 100mm cavity.
- Mainline rail (70–75 dB): target Rw ≥ 48 dB — 6.8mm Stadip Silence at 150mm.
- Heathrow flight path (75–80 dB): target Rw ≥ 52 dB — 10.8mm Stadip Silence at 200mm.
Sound insulation FAQs
What are acoustic window inserts?
Acoustic window inserts are secondary glazing units fitted inside the room reveal, forming a sealed air cavity behind the primary window. The mass of laminated acoustic glass plus the decoupled cavity delivers 40–54 dB Rw sound reduction — the same principle used in recording studios.
How much noise reduction do acoustic window inserts provide?
With 10.8mm Stadip Silence laminated glass and a 150–200mm cavity, we routinely measure 50–54 dB Rw — a perceived reduction of 75–80%. A 60 dB traffic noise level at the window drops to 6–10 dB inside the room, quieter than a library.
What cavity depth is optimal for sound insulation?
Acoustically, wider is better. 100mm is the practical minimum; 150–200mm is optimal; beyond 200mm the mass-air-mass resonance frequency drops below 60 Hz and further gains are minimal. Deep reveals in London townhouses often permit 200mm without joinery modification.
Do acoustic window inserts help with low-frequency noise?
Yes — laminated acoustic glass with PVB interlayer specifically targets the 125–500 Hz band that dominates traffic, rail and aircraft noise. The C_tr correction on our 10.8mm build is only -2 dB, versus -5 to -8 dB for equivalent-thickness IGUs.
Which glass should I specify for traffic, rail or aircraft noise?
For general traffic noise 6.8mm laminate over a 100mm cavity is usually sufficient. For arterial roads, rail corridors and Heathrow flight paths specify 10.8mm Stadip Silence with a 150–200mm cavity, which holds performance across the 125–500 Hz band where those sources concentrate energy.
How much does acoustic secondary glazing cost per window?
Acoustic specification units range from £750 to £1,400 supplied and installed per opening, depending on size, opening type and cavity depth. The uplift over a standard 4mm float specification is typically 30–45%.
Acoustic project reviews
Rated 5.0 out of 5 from 3 client reviews across London.
"Absolutely fantastic service! The secondary glazing has transformed our Victorian home. The noise reduction is incredible — we can barely hear the traffic from the main road now. The installation was professional and clean, and the team respected our period features perfectly."
Sarah Johnson
Kensington, London
"Outstanding results for our office building. The secondary glazing has significantly improved our working environment — much quieter and more comfortable temperature control. The project was completed on schedule and within budget. Highly recommended for commercial properties."
Michael Chen
Canary Wharf, London
"We were sceptical about adding glazing to our listed building, but the team provided a solution that satisfied both conservation requirements and our comfort needs. The reduction in condensation and draughts has been remarkable. Professional service from start to finish."
Emma Thompson
Hampstead, London