The short answer
They solve different problems, so the right answer depends on your home. Double glazing replaces the whole window with a sealed two-pane unit and usually costs around £8,000–£15,000 for a typical three-bed house. Secondary glazing adds a discreet second pane inside the existing window for roughly £3,000–£6,000 across the same home — often 40–60% less. For noise, secondary glazing's wide air gap often outperforms a like-for-like double-glazed swap. And for listed buildings, conservation areas and period homes, secondary glazing is usually the only route that keeps the original window, needs no planning permission and stays reversible. Double glazing wins where you want one sealed unit and the window can be freely replaced.
This is not really 'better or worse' — it is two different jobs. Double glazing replaces the window; secondary glazing keeps it and adds a pane behind it. Here is how they compare on the things that matter.
At a glance
- Secondary glazing~£3,000–£6,000 per home
- Double glazing~£8,000–£15,000 per home
- Noisesecondary often stronger (wide gap)
- Listed / period homessecondary glazing
- One sealed unitdouble glazing
How they compare
Double glazing swaps the whole window for a factory-sealed unit with two panes a few millimetres apart — excellent for everyday warmth and a clean, maintenance-light finish, but it changes the external appearance and costs the most. Secondary glazing leaves the original window in place and fits a second pane on the inside, typically with a much wider air gap. That wide gap is why it is strong on noise, and keeping the original window is why it suits heritage homes — but it is a second frame to open and clean rather than one sealed unit.
| Factor | Secondary glazing | Double glazing |
|---|---|---|
| Typical cost (3-bed) | ~£3,000–£6,000 | ~£8,000–£15,000 |
| Original window | kept | replaced |
| Noise reduction | strong (wide air gap) | good, usually less |
| Listed / conservation | usually suitable | often restricted |
| Reversible | yes | no |
General comparison for guidance; figures depend on your property. Sources: trade cost guides.
When to choose which
- Listed or period home? secondary glazing usually keeps the original window, needs no planning permission and is reversible.
- Noise the main problem? secondary glazing's wide air gap often gives more reduction than a like-for-like double-glazed unit.
- Tighter budget on warmth? secondary glazing improves draughts and heat loss for a fraction of full replacement.
- Window can be freely replaced and you want one sealed unit? double glazing is the cleaner long-term answer.
Not sure which suits your home?
We'll match you with a vetted secondary-glazing installer who surveys your windows and sets out honestly where secondary glazing is the right call and where it is not.
Frequently asked questions
Is secondary glazing cheaper than double glazing?
Usually yes. Secondary glazing for a typical three-bed home is often around £3,000–£6,000, against roughly £8,000–£15,000 to replace the windows with double glazing — commonly 40–60% less for the same property.
Is secondary glazing better than double glazing for noise?
For noise, secondary glazing's wide air gap often outperforms a like-for-like double-glazed unit, because the deep cavity between the panes does more to break up sound. The exact result depends on the glass and the gap.
Which is better for a listed or period home?
Secondary glazing, in most cases. It keeps the original window, normally needs no planning permission and is reversible, whereas replacing the window with double glazing is often restricted on listed and conservation-area properties.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific windows. They are guidance, not a quotation.