Updated 8 June 2026 · 8 min read
If you've been quoted £2,000+ per window for secondary glazing by a London specialist, you've been overcharged. Real 2026 prices for quality installations are £450 to £950 per window. Here's the full breakdown — no commission, no inflated quotes, just what secondary glazing actually costs.
Secondary glazing prices at a glance
| Style | Typical use | Price per window (installed) |
|---|---|---|
| Hinged casement | Standard windows | £450 – £600 |
| Horizontal sliding | Wider openings | £550 – £750 |
| Vertical sliding sash | Period sash windows | £650 – £900 |
| Lift-out / removable | Seasonal use | £400 – £550 |
| Acoustic (10mm+ glass) | Heavy traffic / flight paths | £750 – £950 |
| Conservation grade | Listed buildings | £700 – £950 |
Prices include survey, manufacture, installation and a 10-year insurance-backed guarantee. Based on standard window sizes up to 1.2m × 1.5m. London installations typically sit at the top of these ranges.
What determines the price of secondary glazing?
1. Window size
A standard 600mm × 900mm casement window costs significantly less than a 2m-wide sliding sash unit. Most installers price by area (£/m²), with rates of £280–£420 per square metre being typical in 2026.
2. Glass specification
Standard 4mm float glass is the cheapest option. Common upgrades:
- 6mm toughened: +£40–£70 per window. Required near doors or below 800mm sill height (Building Regs).
- 10mm acoustic: +£120–£180 per window. Adds 3–5 dB of noise reduction.
- Low-E thermal glass: +£60–£90 per window. Improves U-value by 25–30%.
- Laminated security glass: +£90–£140 per window. P1A rated for burglary resistance.
3. Frame finish
Standard white powder-coated aluminium is included in base pricing. Upgrades cost £40–£90 per window:
- Anthracite grey (RAL 7016) — the most popular upgrade
- Any RAL colour to match your existing decor
- Woodgrain effect finishes (oak, mahogany, walnut)
- Dual-colour (different inside vs sightline)
4. Air gap and acoustic performance
The single most important factor in noise reduction is the air gap between your primary window and the secondary unit:
| Air gap | Noise reduction | Best for |
|---|---|---|
| 50–80mm | 35–40 dB | Thermal only |
| 100mm | 42–46 dB | Suburban traffic |
| 150mm | 48–52 dB | Main roads, flight paths |
| 200mm+ | 54+ dB | Heathrow approach, central London |
Source: independent acoustic testing data referenced in BSI guidance on secondary glazing.
Why secondary glazing is cheaper than replacement windows
Replacement double glazing for a 3-bedroom semi runs £8,000 to £15,000. Secondary glazing for the same property typically costs £4,500–£7,500 — roughly half. Here's why:
- No removal cost. Your existing windows stay in place. Replacement glazing requires careful removal, often with making-good of brickwork, plaster and sills.
- No FENSA compliance for the original window. Secondary glazing is a fitted internal unit, not a Building Regulations notifiable replacement.
- Faster installation. A typical 3-window room takes one day vs 2–3 days for replacement.
- Smaller frames. Less aluminium, less glass, fewer hardware components.
When secondary glazing is the only legal option
If your home is in any of these categories, secondary glazing isn't just cheaper — it's typically the only option that will pass planning:
- Grade I or Grade II listed buildings
- Properties in conservation areas
- Buildings under an Article 4 Direction (common in London boroughs like Camden, Hackney and Islington)
- Leasehold flats where the freeholder restricts alterations
In all these cases, secondary glazing is considered reversible and non-invasive, so it typically doesn't require listed building consent — though we always recommend a courtesy check with your local conservation officer.
Whole-house pricing examples
| Property | Windows | Typical cost |
|---|---|---|
| Victorian terrace, suburban | 8 hinged casement | £4,200 – £5,400 |
| Edwardian semi, conservation area | 10 vertical sliding sash | £7,500 – £9,800 |
| Georgian townhouse, Grade II listed | 12 conservation grade | £9,200 – £12,400 |
| 1930s detached, flight path | 14 acoustic 10mm | £11,800 – £14,500 |
How to get an accurate quote
Online calculators give ballpark figures but can't account for the realities of your specific property. We provide free no-obligation home surveys across London and Hertfordshire — we measure, check sill conditions, advise on the right glass specification for your noise issue, and give you a fixed quote with no commission games.
Get your free secondary glazing quote
No commission salespeople. No high-pressure tactics. Just an accurate quote from an installer family-run since 1973.