Secondary Glazing vs Double Glazing
Which is right for your London home? An honest comparison of cost, performance, and suitability for different property types.
Quick Answer
Secondary glazing is better for noise reduction (up to 80% vs 30-40%) and is the only viable option for listed buildings and conservation areas. Double glazing is better for thermal efficiency but requires replacing your original windows and often needs planning permission.
Full Comparison
| Feature | Secondary Glazing | Double Glazing |
|---|---|---|
| Noise reduction | Up to 80% (45-54dB) | 30-40% (25-32dB) |
| Thermal performance | Very good (40-50% heat loss reduction) | Excellent (65-75% heat loss reduction) |
| Cost per window | £200-£400 | £400-£800 |
| Planning permission | Not required | Often required in CAs |
| Listed buildings | Suitable (reversible) | Usually prohibited |
| Preserves original windows | Yes | No (replacement) |
| Installation disruption | Minimal (1 day) | Significant (2-5 days) |
| Reversibility | Fully reversible | Permanent change |
| Security enhancement | Good (extra layer) | Very good (toughened glass) |
| Condensation risk | Low (with proper ventilation) | Very low |
| Lifespan | 25-30 years | 20-25 years |
Noise Reduction: Secondary Glazing Wins
This is where secondary glazing significantly outperforms double glazing. The key is the air gap: secondary glazing creates a gap of 100-200mm between the original window and the secondary unit, compared to just 12-20mm in double glazing.
This larger air gap is far more effective at blocking sound, especially low-frequency noise from traffic, railways, and aircraft. With acoustic laminated glass, secondary glazing can achieve 45-54dB reduction (up to 80% perceived noise reduction), while standard double glazing typically achieves only 25-32dB.
Thermal Performance: Double Glazing Wins (Slightly)
Double glazing has a slight edge on thermal performance because sealed double-glazed units can incorporate argon gas fills and low-emissivity coatings that maximise insulation.
However, secondary glazing still provides substantial thermal improvement — typically reducing heat loss through windows by 40-50%. When combined with draught sealing, secondary glazing can achieve U-values comparable to some double glazing units.
For many London properties, the thermal benefit of secondary glazing is more than sufficient, especially considering that it preserves original windows and doesn't require planning permission.
Which Should You Choose?
Choose Secondary Glazing If...
- Your property is in a conservation area
- Your building is listed (Grade I, II*, II)
- You want to preserve original period windows
- Noise reduction is your primary concern
- You are on a tighter budget
- You rent your property (reversible)
- You want minimal disruption during installation
Choose Double Glazing If...
- Your property has no heritage restrictions
- Your existing windows are beyond repair
- Maximum thermal efficiency is your priority
- You want the lowest maintenance option
- You are planning a full renovation anyway
- Your windows have no historic or aesthetic value
- You want to update the appearance of your home
Not Sure Which Is Right for You?
Book a free survey and we will assess your property, understand your priorities, and give you honest advice on whether secondary glazing is the right solution.
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