Is secondary glazing worth it?
Where it makes sense against replacing windows, what it does for noise, and the cheap film version.
- Difficulty
- beginner
- Time
- 30 min
- Read
- 2 min
Short answer
Worth it where you cannot replace the windows — listed buildings, conservation areas, or where the cost is prohibitive. It is better than double glazing for noise and slightly worse for heat.
Secondary glazing is a second pane fitted inside the existing window. It is often dismissed as a compromise, but for noise it genuinely outperforms modern double glazing, because the wider air gap is what blocks sound.
Step by step
- Work out whether replacement is even possible.Listed buildings and conservation areas frequently prohibit it. Where that applies, secondary glazing is usually the only option rather than a compromise.
- Decide whether heat or noise is the priority.For noise, secondary glazing with a wide gap — 100mm or more — beats double glazing. For heat, double glazing performs better.
- Consider the cost difference.Secondary glazing typically costs substantially less than replacing windows, and can be fitted room by room as budget allows.
- Try the film version first if unsure.Shrink-fit insulation film costs very little per window and lasts a season. It genuinely works and it tells you whether the full version is worth it.
- Check how it will open.You still need to open the window for ventilation and for cleaning. Hinged, sliding and lift-out systems all exist; think about how the room is actually used.
- Think about condensation.The gap needs to be reasonably sealed on the room side and slightly vented to the outside, or moisture condenses between the panes. Ask how a given system handles this.
- Combine it with draught-proofing.Old windows leak air as well as heat. Sealing the original frame first improves the result considerably.
- Get quotes from specialists.It is a specialist trade rather than a general glazing one, particularly for period properties where the fit has to be sympathetic.
Tips
- Insulation film is remarkably effective for a few pounds per window. It is not attractive close up but from across a room it is nearly invisible.
- For a bedroom on a busy road, secondary glazing is often the single most effective improvement available.
- Keep the original windows maintained regardless. Secondary glazing protects them from weathering but does not remove the need for upkeep.
Questions people ask
Is secondary glazing as good as double glazing?
For heat, slightly worse. For noise, generally better — the wider air gap blocks sound more effectively than the narrow gap in a sealed unit.
Can I use it in a listed building?
It is usually the preferred option precisely because it is reversible and leaves the original windows intact. Check with the conservation officer first.