Heritage Acoustic Glazing Specialists
Soundproof Sash Windows LondonSilence the noise. Keep the heritage.
Your original sash windows are beautiful — but they let in every bus, every train, every plane. Our 10.8mm Stadip Silence acoustic secondary glazing fits inside the reveal, achieving STC 50+ without touching your period windows. Listed building approved. No planning permission. Installed in a day.
The London Sash Window Problem
London has more original sash windows than any other city in the world — over 2 million across its conservation areas. They're architecturally irreplaceable. But acoustically? They're the weakest point in your home.
Single-Glazed Sash = 18–22dB STC
Original Victorian and Georgian sash windows were never designed for acoustic performance. A typical single-glazed timber sash achieves just STC 18–22 — allowing virtually all traffic, rail, and aircraft noise straight through.
Listed & Conservation Restrictions
In boroughs like Westminster, Camden, Kensington & Chelsea, and Richmond, external window alterations require Listed Building Consent. Replacing sash windows with double glazing is almost always refused by conservation officers.
Draughts & Heat Loss
Original sash windows lose up to 40% of a home's heat through gaps in the sliding mechanism, meeting rail, and putty line. London homeowners spend hundreds more per year on heating than they need to.
Security Vulnerabilities
Single-glazed sash windows with original catches offer minimal security. Secondary glazing adds a fully independent internal barrier with multi-point locking — a significant deterrent.
How We Soundproof Sash Windows
We don't replace your sash windows — we add a precision-engineered acoustic panel inside the reveal. The result is STC 45–54: 2–3× the noise reduction of replacement double glazing.
CNC-Cut to the Millimetre
Period sash windows settle and warp over 100+ years. Every frame is laser-measured and CNC-machined to fit reveals that are rarely square — ensuring an airtight acoustic seal even on 200-year-old windows.
20mm Slimline Aluminium Frames
Our ultra-slim frames sit within the existing window reveal, virtually invisible from inside the room. The narrow sightlines mirror original timber glazing bars so they don't disrupt the period aesthetic.
Heritage Colour Matching
Frames are powder-coated to match your existing paintwork — Farrow & Ball, Little Greene, or any RAL colour. Conservation officers approve our installations because they're discrete, internal, and fully reversible.
Vertical Slider Mechanism
For sliding sash windows, our vertical slider secondary panels replicate the original up-and-down movement. Spring balances ensure smooth operation without weights or cords — and the sliding action allows ventilation when needed.
The Glass: 10.8mm Stadip Silence
An asymmetric laminate (6.4mm + 4.4mm float glass bonded with an acoustic PVB interlayer) specifically tuned to dampen traffic frequencies (250–2000Hz) and aircraft rumble (63–500Hz). Combined with a 100–200mm air gap from your original sash, this creates the mass-air-mass decoupling that delivers up to 54dB noise reduction.
Sash Window Soundproofing: The Numbers
Side-by-side comparison: keeping your original sash, replacing with double glazing, or adding acoustic secondary glazing.
| Metric | Original Sash | Double Glazed Sash | Secondary Glazing |
|---|---|---|---|
| Noise Reduction (STC) | 18–22 dB | 28–32 dB | 45–54 dB |
| Heat Loss Reduction | Baseline | 40–50% | 60–65% |
| Preserves Original Window | Yes | No ❌ | Yes ✅ |
| Listed Building Compliant | N/A | Rarely | Always ✅ |
| Planning Permission | N/A | Usually required | Never required |
| Installation Time (per window) | N/A | 2–4 hours + scaffolding | 30–45 minutes |
| Reversible | N/A | No | Yes ✅ |
| Cost Per Window | Existing | £1,200–£2,500 | £450–£900 |
London's Best Sash Window Boroughs — We Cover Them All
The boroughs with the highest concentration of original sash windows are also London's noisiest. Here's where we work most frequently.
Kensington & Chelsea
RBKC LLBCO streamlines consent for internal glazing
Westminster — Belgravia
Georgian townhouses with original crown glass sashes
Westminster — Mayfair
Park Lane traffic + Heathrow flight path
Camden — Hampstead
HGST conservation standards for Heath-side properties
Islington & Canonbury
Georgian terraces on Upper Street bus corridors
Richmond & Twickenham
Heathrow approaches over Georgian riverside homes
Notting Hill & Holland Park
Italianate villas with oversized sash windows
London Sash Window Transformations
Real results from real period properties — with before and after decibel measurements.
"Our 1820s Georgian townhouse has 14 original sash windows. English Heritage wouldn't allow any external changes. The secondary glazing went in over two days — the conservation officer was delighted. We went from hearing every bus on Buckingham Palace Road to near-total silence."
Margaret & Christopher D.
Belgravia, SW1 · Grade II* Georgian townhouse
Measured: 72dB → 26dB
"Our Victorian villa sits 30 metres from the Overground line. The sash windows rattled with every train. After the vertical slider secondary glazing was installed, the trains are completely inaudible. The frames match the original Farrow & Ball 'Railings' colour perfectly."
Oliver & Sophie H.
Hampstead, NW3 · Grade II Victorian villa
Measured: 68dB → 24dB
"I'm a consultant who works from home. Upper Street traffic made video calls impossible with windows facing the road. The slimline secondary panels reduced road noise to library levels. My clients can't tell I'm in central London."
Dr. Rebecca M.
Islington, N1 · Georgian terrace, conservation area
Measured: 65dB → 28dB
Sash Window Soundproofing Prices
All-inclusive: survey, bespoke frames, glass, seals, installation, and colour matching.
Standard Sash
From £450
per sash window, installed
6.4mm laminate. Fixed or lift-out panel. STC 38–42. Ideal for moderate road noise.
Premium Acoustic Sash
From £650
per sash window, installed
10.8mm Stadip Silence. Vertical slider. STC 45–54. Maximum noise reduction.
Heritage Bay Sash
From £750
per sash window, installed
Multi-panel bay window with angled returns. CNC-cut to heritage tolerances.
Soundproof Sash Windows — FAQs
Ready to Soundproof Your Sash Windows?
Book your free noise survey. We'll measure the decibels, assess your sash windows, and give you a fixed-price quote — with heritage colour matching included.