Secondary Glazing vs Double Glazing
An honest, data-driven comparison of noise reduction, cost, thermal performance, and heritage suitability — so you can choose the right solution for your London property.
54 dB
Max noise reduction
40–60%
Cost saving vs replacement
30 min
Install per window
100%
Heritage approved
Head-to-Head Comparison
How secondary glazing and double glazing compare across every metric that matters.
| Feature | Secondary Glazing | Double Glazing |
|---|---|---|
| Noise reduction (STC rating) | STC 45–54 (up to 54 dB with 10.8 mm Stadip Silence) | STC 26–33 (standard sealed units) |
| Cost per window | £300–£900 | £400–£1,200 |
| Installation time | 20–30 minutes per window | 1–2 days per window |
| Disruption to home | Minimal — fitted from inside, no scaffolding | High — scaffolding, removal of existing frames |
| Listed building / conservation area | Fully reversible, no planning permission needed | Usually requires Listed Building Consent |
| Thermal performance (U-value) | 0.8–1.2 W/m²K (with 100 mm+ air gap) | 1.1–1.6 W/m²K (standard sealed unit) |
| Condensation control | Excellent — warm inner pane prevents misting | Good — sealed unit prevents internal misting |
| Security | Additional barrier with independent locks | Multi-point locking on new frames |
| Aesthetic impact | Virtually invisible 20 mm slimline frames | New frames may alter original character |
| Lifespan | 15–25+ years | 20–30 years |
| ROI timeline | 3–5 years | 10–15 years |
STC Noise Ratings Compared
Sound Transmission Class (STC) measures how effectively a window blocks airborne noise. Every 10-point increase roughly halves perceived loudness.
| Glazing Type | STC Rating | Noise Reduction |
|---|---|---|
| Single glazing (4 mm) | STC 26 | ~26 dB |
| Standard double glazing (4-12-4) | STC 28 | ~28 dB |
| Enhanced double glazing (6-16-4) | STC 32 | ~32 dB |
| Triple glazing (4-8-4-8-4) | STC 33 | ~33 dB |
| Secondary glazing — 6.4 mm laminate | STC 40 | ~40 dB |
| Secondary glazing — 10.8 mm Stadip Silence BEST | STC 50+ | ~54 dB |
STC ratings based on laboratory testing of complete window assemblies including frame, glass, and air gap.
Cost Comparison by Property Type
Real-world project costs for London properties. Secondary glazing prices include supply, bespoke manufacture, and professional installation.
| Property Type | Secondary Glazing | Double Glazing | Saving |
|---|---|---|---|
| 1-bed flat (3–4 windows) | £1,200–£2,800 | £1,600–£4,800 | Up to 50% |
| 2-bed Victorian terrace (5–7) | £2,500–£5,500 | £3,500–£8,400 | Up to 45% |
| 3-bed semi (8–10 windows) | £4,000–£9,000 | £6,400–£12,000 | Up to 40% |
| Listed home (6–12 windows) | £5,400–£14,000 | Often not permitted | N/A |
Which Should You Choose?
The right answer depends on your property, budget, and noise levels.
Choose Secondary Glazing When…
- You live near a busy road, railway, or flight path and need maximum noise reduction (up to 54 dB)
- Your property is listed or in a conservation area
- You want to keep original period windows (sash, casement, bay)
- You need a fast, non-disruptive installation
- Budget is a priority — 40–60% cheaper than replacement
- You want to boost your EPC rating without altering the building fabric
Choose Double Glazing When…
- You're building a new-build or extension with no existing windows
- Existing windows are beyond repair (rotten frames, failed seals)
- You want a single-pane solution with integrated ventilation trickle vents
- Your property has no heritage or planning restrictions
Frequently Asked Questions
Expert answers to the most common comparison questions.
Not Sure Which Is Right for You?
Book a free noise survey — we'll measure your exact dB levels, assess your windows, and recommend the most cost-effective solution. No obligation.