Secondary glazing: the option nobody quotes you for
Last reviewed: July 2026 · Fitted prices incl. VAT
Secondary glazing is a discreet second pane fitted to the room side of your existing window. The original window stays exactly as it is — which is why this is the standard route for listed buildings, conservation areas, and serious noise problems. Fitted, it costs £250–£450 per window; DIY magnetic systems start at £50. Window companies rarely mention it because a replacement window sells for £450–£750. Here is the honest comparison.
What it costs
| System | Typical cost per window | Notes |
|---|---|---|
| Fitted aluminium secondary glazing | £250 – £450 | Slim frames, hinged or horizontal-sliding panels, made to measure |
| DIY magnetic / clip-on acrylic | £50 – £150 | Removable panels; effective for draughts, modest for noise |
Large panes, shaped or curved windows, and openable vertical sliders price above the standard band. As with all glazing work, whole-house jobs cost less per window than one-offs.
Secondary glazing vs replacement double glazing
| Secondary glazing | Replacement double glazing | |
|---|---|---|
| Cost per window | £250 – £450 | £450 – £750 (uPVC) |
| Original window | Untouched — reversible | Removed and replaced |
| Listed / conservation | Usually fine (confirm locally) | Often refused or restricted |
| Noise reduction | Excellent — the wide air gap is the advantage | Good |
| Heat retention | Good improvement over single glazing | Best — engineered sealed cavity |
| Building Regs sign-off | Not required (internal addition) | Required — FENSA/CERTASS self-certified |
Where secondary glazing earns its keep
- Listed buildings and conservation areas — the original windows stay; consent problems mostly disappear (always confirm with the conservation officer first).
- Noise corridors — busy roads, flight paths, town centres. The wide gap between original window and secondary pane is what kills sound.
- Single-glazed period sashes you want to keep — the draught-proofing effect alone transforms comfort.
- Rented and short-tenure homes — DIY magnetic panels are removable and take the worst edge off winter without capital works.
Frequently asked questions
How much does secondary glazing cost per window?
Professionally fitted secondary glazing typically costs £250–£450 per window for a standard aluminium-framed panel. DIY magnetic or clip-on acrylic systems run £50–£150 per window. Large windows, curved panels and openable sliding units sit above the standard band.
Is secondary glazing as good as double glazing?
For heat, modern double glazing performs better because the sealed cavity is engineered and gas-filled. For noise, secondary glazing often wins — the much larger air gap between the original window and the secondary pane damps sound more effectively than the narrow cavity in a double-glazed unit.
Can I fit secondary glazing in a listed building or conservation area?
Usually yes — that is its main market. Because secondary glazing is fitted to the inside and leaves the original window untouched, it typically does not need listed building consent, though you should always confirm with your local conservation officer before ordering.
Does secondary glazing stop condensation?
It usually reduces condensation on the original window by keeping the inner surface warmer, but ventilation matters: trapped moist air between the panes can condense on the cold original glass. Good installations include trickle ventilation or breathable gaps to manage this.
Sources: cost bands compiled July 2026 from published UK installer and glazing price guides (Checkatrade, Which? cost data), cross-checked against regional quote data. Heritage guidance: consult your local authority conservation officer before altering windows in listed buildings.