Question 1

Is secondary glazing better than double glazing for noise?

Accepted Answer

Yes. Secondary glazing with 10.8 mm Stadip Silence glass achieves STC 50+ (up to 54 dB reduction), significantly outperforming standard double glazing (STC 28–33). The 100–200 mm air gap between the existing window and the secondary panel 'decouples' sound vibrations far more effectively than the narrow 12–16 mm gap inside a sealed double-glazed unit.

Question 2

How much cheaper is secondary glazing than double glazing?

Accepted Answer

Secondary glazing is typically 40–60% cheaper. A standard casement window costs £300–£500 for secondary glazing versus £400–£1,200 for double glazing replacement. You also avoid scaffolding, skip tracing, and planning application fees — especially relevant for listed buildings.

Question 3

Can I have secondary glazing and double glazing together?

Accepted Answer

Yes. Adding secondary glazing in front of existing double glazing creates a triple-barrier system that can achieve exceptional noise reduction (50+ dB) and U-values below 1.0 W/m²K. This is common in London properties on major A-roads or under Heathrow flight paths.

Question 4

Does secondary glazing affect property value?

Accepted Answer

Positively. Effective soundproofing adds 5–15% to property values in noise-affected London areas. Secondary glazing also improves EPC ratings through better thermal performance, which is increasingly important for buyers and landlords meeting MEES regulations.

Question 5

Do I need planning permission for secondary glazing?

Accepted Answer

Almost never. Because secondary glazing is internal and fully reversible, it does not require planning permission — even in conservation areas or on Grade II listed buildings. This is a key advantage over double glazing replacement, which typically requires Listed Building Consent.

Question 6

What is an STC rating and why does it matter?

Accepted Answer

STC (Sound Transmission Class) measures how well a building element blocks airborne sound. Higher is better. Standard double glazing scores STC 28–33, while our 10.8 mm acoustic secondary glazing scores STC 50+. Every 10-point increase roughly halves perceived loudness, so the difference between STC 30 and STC 50 is dramatic.

Question 7

How long does secondary glazing last compared to double glazing?

Accepted Answer

Quality secondary glazing lasts 15–25+ years with minimal maintenance. Double glazing sealed units typically last 20–30 years, but the sealed gas cavity can fail in 15–20 years causing internal misting. Secondary glazing has no sealed cavity to fail.

Question 8

Which is better for thermal insulation?

Accepted Answer

Both perform well, but secondary glazing with a 100 mm+ air gap achieves U-values of 0.8–1.2 W/m²K, comparable to or better than standard double glazing (1.1–1.6 W/m²K). The wider air gap provides superior thermal decoupling and can reduce heating bills by 10–20%.

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

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

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

Secondary Glazing vs Double Glazing

Head-to-Head Comparison

STC Noise Ratings Compared

Cost Comparison by Property Type

Which Should You Choose?

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Frequently Asked Questions

Not Sure Which Is Right for You?

Sources & References