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- Secondary Glazing
Secondary glazing in London: turn the city down.
Glazing London fits made-to-measure secondary glazing across Central & North London: a discreet second window inside your existing one that cuts traffic noise by up to 80% and roughly halves heat loss. Ideal for sash windows, period homes and listed buildings. Free surveys and quotes 24/7 on 07399 253464.
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Typical noise reduction
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Changes to original windows
How it works
A second window, a wall of still air.
Secondary glazing is a slim aluminium-framed pane fitted to the inside of your existing window reveal. Sound is carried by vibration, and what kills it is the air gap: at 100-200mm, far wider than the 16-20mm cavity in a double glazed unit, sound waves lose most of their energy crossing it.
For the best results at London's noisiest addresses (flight paths, main roads, night-time high streets) we glaze the secondary panel with 6.4mm or 6.8mm acoustic laminated glass in a different thickness to the original pane, so the two never resonate at the same frequency. Typical measured reductions are 45-50dB, which most people describe as the traffic simply disappearing.
The same still-air layer roughly halves heat loss and stops draughts dead, which is why it pairs so well with sash window repair and draught-proofing.
Four styles
Made to match how your windows open.
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Rises and falls exactly like a box sash, with balanced springs. The classic choice behind period joinery.
Best for: sash windowsLift-out panel
A light panel that unclips entirely in seconds. Simple, economical, and easy to store in summer.
Best for: bedrooms & budget jobsFixed panel
Sealed shut for maximum acoustic and thermal performance where the window never needs to open.
Best for: landings, studios, stairwells
Heritage & listed buildings
Keep the 1890s glass. Lose the 2026 noise.
Secondary glazing is fitted internally and is fully reversible: the original windows, glass and joinery are untouched. That's why it's the approach conservation officers most commonly recommend, and in most cases it needs no planning consent, even in conservation areas. For listed buildings we still recommend a quick word with your conservation officer, and we're happy to supply drawings and specifications for the application if consent is required.
Slim frames are powder-coated to blend with your reveals, sightlines are aligned with the original glazing bars, and secondary glazing for sash windows keeps both sashes working. If the sashes themselves are rattling or rotten, our sash window repair team can overhaul them in the same project.
Where we fit it most
- Victorian & Georgian sash terraces
- Mansion blocks and conversions with strict freeholder rules
- Listed buildings & conservation areas across North London
- Flats over high streets, main roads and rail lines
- Home offices and studios that need quiet, not new windows
The honest comparison
Secondary glazing vs replacement double glazing
| Factor | Secondary glazing | Replacement double glazing |
|---|---|---|
| Noise reduction | 45-50dB, the acoustic winner | ~30-35dB |
| Thermal performance | Heat loss roughly halved; near-double-glazing with low-E glass | Best-in-class U-values, especially with new frames |
| Original windows | Untouched and reversible | Removed and replaced |
| Listed buildings / conservation | Usually no consent needed | Often refused or heavily conditioned |
| Typical cost per window | Roughly half the cost | Higher (frames, cills, making good) |
| Disruption | 45-90 minutes per window, internal only | Days, plus external access and redecorating |
| Condensation on old glass | Sharply reduced | Eliminated (new sealed units) |
If your existing double glazing has failed rather than the windows being single glazed, misted unit replacement is usually the better-value fix. And when replacement genuinely is the right answer, our FENSA-certified installation team will quote it straight. Either way, the survey and the advice are free.
Questions
Secondary glazing, answered
How much noise does secondary glazing block?
Correctly specified secondary glazing achieves reductions of around 45-50dB, up to 80% of perceived noise, because the wide air gap (100-200mm) and different glass thickness break the sound path. That outperforms standard replacement double glazing, which manages roughly 30-35dB.
Can I fit secondary glazing in a listed building or conservation area?
Usually yes, and usually without planning consent: secondary glazing is fitted internally and is reversible, so the original windows are untouched. It is the approach heritage officers most commonly recommend for listed buildings, though for listed properties we always advise confirming with your conservation officer first.
Does secondary glazing work with sash windows?
Yes: vertical sliding secondary glazing mirrors the operation of a box sash, so you can still open both. It is the standard solution for Victorian and Georgian sash windows in London and sits discreetly behind the existing joinery.
Will secondary glazing cut condensation and heat loss?
Yes. The still air layer roughly halves heat loss through the window, and warming the inner surface sharply reduces condensation on the original glass. With low-E glass specified, thermal performance approaches that of double glazing.
Is secondary glazing cheaper than replacement double glazing?
Typically yes, often around half the cost per window, with no structural work, no FENSA notification needed and no change to the building's appearance. For noise specifically it performs better than replacement double glazing.
How long does secondary glazing installation take?
After a free measured survey, panels are made to measure in around two weeks and most installations are completed in a day. Each window takes roughly 45-90 minutes with minimal disruption. Urgent problem with a window right now? Call our 24/7 emergency line.