Slim double glazing for sash windows
Slim double-glazed units fitted into your existing sashes for warmth and quiet, with the original window kept — £980 + VAT per window.
Slim double-glazed units can be fitted into most original sashes without replacing the window. The old glass comes out, the rebate is prepared, the new unit is bedded in and the sash weights are re-balanced to carry the extra weight. £980 + VAT per window.
What is involved
- Survey to check the rebate depth and the condition of the sash
- Single glass removed and the rebate prepared or deepened
- Slim double-glazed unit bedded, beaded and sealed
- Weights changed so the heavier sash still balances
- Draught-proofing fitted at the same time if you want it
Doing this at the same time as draught-proofing or a full restoration saves a second visit and a second set of access costs.
Frequently asked questions
Can you put double glazing in my existing sash windows?
Usually yes. Slim double-glazed units are made to fit the existing rebate, so the original sash, glazing bars and frame all stay. Where the rebate is too shallow we deepen it or make a new sash to match the original profile.
How much does it cost?
£980 + VAT per window. That includes making good and reglazing, and a fixed written quote after the survey.
Will it look different?
Slim units are around 11–14mm against 4mm single glass, so the sash sits a touch heavier. From the street it reads as a traditional window — which is why this route is accepted in many conservation areas where replacement windows are not.
Is it warmer than secondary glazing?
It performs better than single glazing and keeps the window working as designed. Secondary glazing can insulate slightly better but adds a second frame inside and gets in the way of opening the sash.
Do the weights need changing?
Yes. The new glass is heavier, so the sash weights are changed or added to so the window still balances. That is part of the price.
Other sash window services
Double glazing near you
If slim double glazing is not an option
Some sashes are too slender to take a sealed unit without being weakened, and some conservation officers will not accept one at all. In both cases secondary glazing gives you the insulation and much better noise reduction with nothing removed from the original window. We compare the two properly in secondary glazing vs double glazing, and explain the consent position in listed buildings and conservation areas.