Published April 2026 · International Windows Group · 10 minute read

Living in London is many things, but quiet is rarely one of them. Aircraft on the Heathrow westerly approach, the constant draw of traffic on the Westway and the South Circular, Overground trains threading through Hampstead and Hackney, the Underground rumbling below half the city, and the simple density of a capital that never fully sleeps — all of it ends up at one place: the window. For most London homeowners, the window is the single largest acoustic weakness in the building envelope, and the single most effective component to upgrade if the goal is to reclaim a calmer interior.

At International Windows Group, we specify acoustic glazing solutions across central, North and West London — from period sash window restorations on properties under the Heathrow flightpath to contemporary triple-glazed casements on residential developments alongside arterial roads. This guide explains how acoustic glazing actually works, what performance to expect, and how to match the right specification to the right property without compromising either heritage character or modern comfort.

Understanding Sound Through Glass

Sound transmission through a window is measured in decibels (dB) of reduction, typically expressed as the weighted sound reduction index Rw. The higher the number, the better the window blocks noise. The decibel scale is logarithmic: a reduction of 10 dB roughly halves the perceived loudness, and a reduction of 20 dB makes the source feel about a quarter as loud.

Typical real-world performance:

Single-glazed Victorian sash: 23 dB to 27 dB Rw.
Standard double glazing (4-12-4 mm): 28 dB to 31 dB Rw.
Acoustic double glazing (6-16-4 mm with laminated panes): 35 dB to 38 dB Rw.
High-specification acoustic double glazing (8-20-6 mm with acoustic interlayers): 40 dB to 43 dB Rw.
Acoustic triple glazing: 42 dB to 46 dB Rw.
Acoustic secondary glazing combined with primary windows: 50 dB to 55 dB Rw.

For most London residential applications, the practical target is in the range of 36 to 42 dB Rw — a step change in audible noise that is achievable without resorting to extreme glazing thicknesses or sacrificing the property’s character.

The Three Levers of Acoustic Performance

A common mistake is assuming that thicker glass automatically means a quieter window. In reality, three independent factors determine acoustic performance, and the strongest specifications combine all three.

Glass Mass

Heavier glass blocks more sound. Increasing the thickness of one or both panes in a double glazed unit improves Rw, particularly at low frequencies (traffic rumble, train pass-bys). Moving from 4 mm to 6 mm or 8 mm glass typically adds 2 to 4 dB.

Asymmetric Glazing

Two panes of identical thickness share the same resonant frequency and transmit sound at that frequency efficiently. Asymmetric units — for example 6 mm outer pane paired with 4 mm inner pane — have offset resonances and perform measurably better. Almost every quality acoustic specification uses asymmetric panes.

Laminated and Acoustic Interlayers

The single largest performance gain comes from laminated glass with an acoustic interlayer (PVB or specialist acoustic PVB such as Trosifol SC). The interlayer dampens vibration across the glass surface and dramatically improves performance, especially in the speech frequency range (500 Hz to 4000 Hz). A laminated acoustic pane will outperform a thicker monolithic pane by 3 to 5 dB, often without any visible difference at the doorstep.

The cavity width between panes matters less than people assume. Beyond 16 mm, additional cavity adds little acoustic benefit and begins to compromise thermal performance through convection within the unit.

Acoustic Glazing for Period Properties

The biggest myth in acoustic glazing for London is that period properties cannot be acoustically improved without losing their character. With current technology, this is no longer the case.

Slimline Acoustic Double Glazing in Original Sashes

Slim double glazed units with overall thicknesses of 12 to 14 mm can be retrofitted into restored or reproduction Victorian and Edwardian timber sash windows. With acoustic interlayers and asymmetric panes, these units deliver 33 to 36 dB Rw — close to standard modern double glazing, with the visible profile of an original Victorian sash. For full restoration context, see our bespoke sash window guidance.

Bespoke Replacement Sashes with Full Acoustic Specification

Where the original sashes are beyond restoration and replacement is the right path, bespoke timber sashes with deeper rebates can accept full-thickness acoustic units (24 to 28 mm overall) with laminated outer panes. Performance reaches 38 to 41 dB Rw while the visible profile remains period-correct.

Secondary Glazing as an Alternative

For listed buildings where any modification to the original sash is constrained by Listed Building Consent, slim secondary glazing fitted internally — typically 6 to 10 mm laminated glass in an unobtrusive aluminium frame — combined with the original single-glazed sash delivers 45 to 50 dB Rw. This is among the highest performance available on the residential market and preserves the original window in its entirety. Secondary glazing is also reversible, which conservation officers strongly favour.

Draught Sealing Matters as Much as Glass

An acoustic window with a poor seal underperforms a basic double glazed unit with excellent seals. Sound takes the path of least resistance, and a 1 mm gap around the perimeter of a sash transmits more noise than the entire glazing area. Professional brush-pile and EPDM sealing is integral to every acoustic upgrade we deliver.

Acoustic Glazing for Modern and Contemporary Properties

For non-listed and non-conservation-area properties, the specification options widen considerably:

Casement windows. Engineered timber casements with deep rebates accept full-specification acoustic units. Timber casement windows with 8 mm laminated outer pane, 16 mm cavity and 6 mm laminated inner pane reach 41 dB Rw.
Tilt and turn windows. Multi-point compression seals on tilt and turn frames deliver excellent perimeter performance. Combined with acoustic glazing, these are among the highest-performing window types on the market.
French and bifolding doors. Acoustic glazing in timber French doors and timber bifolding doors mitigates the acoustic penalty of large glazed openings, particularly important for properties with garden frontage onto noise sources.

Property-Specific Considerations Across London

Heathrow Flightpath

Properties under the Heathrow westerly approach (Chiswick, Hammersmith, Acton, Ealing, Brentford, Richmond) experience aircraft noise concentrated in the 100 to 1000 Hz range. Acoustic glazing with 8 mm laminated outer panes and acoustic interlayers is the appropriate baseline. Older Heathrow Sound Insulation Grant Scheme installations (1970s and 1980s) are typically now well below current performance standards and warrant upgrade.

Arterial Roads

Properties on the Westway, Marylebone Road, Edgware Road, the South Circular and Old Kent Road experience continuous low-frequency rumble from traffic, punctuated by motorbike acceleration and bus pass-bys. Asymmetric acoustic units with mass-loaded outer panes (8 to 10 mm) deliver the strongest performance against this profile.

Rail Lines

Properties near Overground, mainline and Underground routes (Hackney, Stratford, Brixton, Camden, Maida Vale) experience intermittent high-amplitude pass-bys with distinctive low-frequency content. Acoustic specifications must address both the sustained level and the impact-style transient peaks. Triple glazing or secondary glazing is often justified on properties with line-of-sight to elevated tracks.

Inner-City Mixed Noise

Properties in central London (Soho, Covent Garden, Mayfair, Marylebone) face a mixed environment — restaurant extraction fans, late-night pedestrians, deliveries, taxi engines. The full acoustic spectrum is loaded, and high-mass laminated double glazing combined with effective seals usually outperforms a more expensive triple-glazed unit with average sealing.

Frame and Installation: The Other Half of the System

An acoustic glazing unit is only as good as the frame and installation that hosts it. Several details determine whether the on-site performance matches the laboratory rating:

Frame mass. Lightweight aluminium frames transmit sound more readily than dense timber. Engineered timber frames with hardwood facings are acoustically superior in residential applications.
Perimeter sealing. Closed-cell foam, acoustic mastic or low-modulus silicone applied between the frame and the masonry reveal closes the most common acoustic leak path.
Reveal detailing. A continuous plaster or timber reveal that contacts the frame is essential. Loose or untreated reveal cavities undermine the entire installation.
Threshold detailing. On doors, the threshold is the weakest acoustic link. Multi-point compression seals and acoustic threshold strips are standard on our acoustic door specifications.
Trickle vents. Untreated trickle vents transmit substantial noise. Acoustic trickle vents with internal labyrinth detailing reduce ventilation noise by 30 to 40 dB.

Acoustic Glazing and Thermal Performance

A frequent concern is whether an acoustic upgrade compromises thermal performance. In modern engineering, the two are largely complementary:

Argon or krypton gas fills inside acoustic units improve U-values without affecting acoustic performance.
Low-emissivity coatings on the inner face of the outer pane reduce heat loss without acoustic penalty.
Warm-edge spacer bars maintain acoustic seals while improving edge thermal performance.

A correctly specified acoustic double glazed unit typically achieves U-values in the 1.2 to 1.5 W/m²K range. Acoustic triple glazing can reach 0.8 W/m²K. A separate discussion of double versus triple glazing trade-offs is available in our double vs triple glazing guide.

Costs and What Drives Them

Acoustic glazing carries a premium over standard double glazing, driven primarily by laminated panes and acoustic interlayers. As a guide for London residential projects:

Standard double glazing in a bespoke timber window: baseline cost.
Acoustic double glazing (laminated outer pane): 10% to 15% premium over baseline.
High-specification acoustic double glazing (laminated both panes, acoustic interlayer): 20% to 30% premium.
Acoustic triple glazing: 35% to 50% premium.
Secondary glazing system (in addition to retained primary window): typically £600 to £1,500 per opening installed.

For most London residential applications, a high-specification acoustic double glazed unit in a well-sealed timber frame represents the strongest value point. Triple glazing is rarely cost-justified on acoustic grounds alone.

Use our timber windows and doors cost calculator for an initial estimate of your project, or review the technical detail in our technical drawings.

Frequently Asked Questions

Will acoustic glazing make my home silent?

No window can deliver a fully silent interior. A high-specification acoustic upgrade in a London property typically reduces audible external noise to a comfortable, non-intrusive background level — sleeping, working from home and conversation become substantially easier. The transformation is most pronounced where the existing windows are single glazed.

Can I retrofit acoustic glazing into my existing sash windows?

If the existing sashes are sound and have sufficient rebate depth, slimline acoustic double glazed units can be retrofitted. Where the rebates are too shallow, the sashes must be replaced with bespoke reproductions deep enough to accept the units.

Is triple glazing always better than double for noise?

No. A correctly specified acoustic double glazed unit with laminated panes outperforms standard triple glazing in the speech and traffic frequency ranges. Triple glazing has marginal acoustic advantage only when both side panes are laminated and asymmetric.

What’s the difference between acoustic glazing and secondary glazing?

Acoustic glazing is built into the primary window. Secondary glazing is an additional internal window installed inboard of the primary. Secondary glazing typically delivers higher absolute acoustic performance because it adds an additional sealed air gap of 100 mm or more, but it requires internal space and adds visual mass to the room. For listed buildings, secondary glazing is often the only consented option.

Will acoustic glazing affect the look of my Victorian or Edwardian property?

With slimline units in correctly proportioned timber sashes, the visible difference at street level is minimal. Conservation officers routinely approve acoustic upgrades on period properties where the visible profile is preserved.

How long does acoustic glazing last?

The acoustic interlayer performance is stable for the design life of the sealed unit — typically 25 to 30 years. The timber frame, with proper maintenance, will outlast the glazing unit by several decades and accept reglazing when needed.

Specialist Acoustic Glazing Across London

Whether your property is a Victorian terrace under the Heathrow flightpath, an Edwardian villa near the South Circular, a Georgian townhouse on a busy Westminster street, or a contemporary build adjacent to a rail corridor, the right acoustic specification will materially change how the space feels. The work begins with an honest assessment of the dominant noise sources, the constraints of the property’s planning status, and the homeowner’s performance expectations.

To discuss your project, request a survey or obtain a tailored specification, visit our contact page. Completed installations across Greater London are documented in our portfolio.