Double glazed sash windows typically cost £600 to £1,200 per window in uPVC, £1,200 to £2,500 in softwood and £1,800 to £3,500 in hardwood or Accoya, fitted, in 2026. If your existing sashes are sound, adding slim double glazing or vacuum glass to them can cost £600 to £1,500 instead. This guide compares every option so you can choose the right one for your home and budget.
Prices at a glance
| Option | Typical cost per window, fitted |
|---|---|
| New uPVC double glazed sash | £600 to £1,200 |
| New softwood timber double glazed sash | £1,200 to £2,500 |
| New hardwood or Accoya double glazed sash | £1,800 to £3,500 |
| Slim or vacuum glazing fitted into existing sashes | £600 to £1,500 |
| Secondary glazing (an alternative) | £180 to £400 |
London and the South East are typically 20 to 30% higher. Acoustic, low-E or decorative glass adds around 10 to 25%.
Typical prices by window size (softwood)
| Window | Typical cost, fitted |
|---|---|
| Small one-over-one | £1,000 to £1,500 |
| Standard two-over-two | £1,300 to £2,000 |
| Large six-over-six Georgian | £1,800 to £2,800 |
| Tall Victorian bay, per light | £1,500 to £2,500 |
| Full three-light bay | £4,500 to £8,000 |
Choosing the glass
- Standard double glazing (around 24mm units): best value and insulation, but thicker glazing bars.
- Slim double glazing (around 12 to 14mm): allows slimmer bars that look right on period homes; the usual choice in conservation areas.
- Vacuum glazing: only a few millimetres thick, insulates very well and can often go into existing sashes; costs more.
- Triple glazing: rarely used in sashes because of the weight and thickness.
Ask for the window’s U-value or energy rating. Replacement windows must meet building regulations, and an installer registered with a scheme such as FENSA or CERTASS can self-certify the work.
New windows or upgrade the old ones?
If your existing timber sashes are in good condition, upgrading them keeps the original frames and usually costs less. See can you double glaze existing sash windows? If they are rotten or have been badly altered, new windows make more sense. Our guide to sash window repair or replacement will help you decide.
Timber or uPVC?
uPVC costs roughly half as much and needs no painting, but looks chunkier and is often refused on period homes in conservation areas. Timber looks authentic, lasts longer and can be repaired. Compare them in uPVC vs timber sash windows, and the different timbers in timber sash windows: softwood, hardwood or Accoya.
Will double glazing save money?
Replacing draughty single glazing with well-fitted double glazing makes rooms warmer, quieter and less prone to condensation, and lowers heating bills. The exact saving depends on your home, the glass and how draughty the old windows were. If cost is the main concern, draught-proofing and secondary glazing give much of the benefit for less money.
Do you need permission?
- Most houses outside conservation areas can replace windows without planning permission.
- In conservation areas, flats and houses with Article 4 directions often need permission. See double glazed sash windows in a conservation area.
- Listed buildings need listed building consent. See our listed building windows guide.
Questions to ask for an accurate quote
- What is the glass specification, unit thickness and U-value?
- Are the glazing bars real, bonded with spacer bars, or stick-on?
- Weights and pulleys or spiral balances?
- Which timber, and what paint system?
- What is included: fitting, making good, disposal and draught-proofing?
- What guarantees cover the frame, glass and workmanship?
Get quotes for double glazed sash windows or browse double glazed sash window companies.
Frequently asked questions
How much do double glazed sash windows cost?
Typically £600 to £1,200 per window in uPVC, £1,200 to £2,500 in softwood and £1,800 to £3,500 in hardwood or Accoya, fitted, in 2026.
How much does it cost to replace all the sash windows in a house?
For a typical three-bedroom terrace with six windows, expect roughly £4,500 to £18,000, depending on the material and glazing.
Are double glazed sash windows worth it?
Usually, yes, if your current windows are draughty or beyond repair. If they are sound, upgrading the existing sashes or adding secondary glazing may be better value.
Can double glazed sash windows look traditional?
Yes. Slim double glazing, real or bonded glazing bars and traditional mouldings make them very hard to tell from originals.
Sources
Prices from the Best Builders sash window cost guide, updated September 2026.
Plain-English guides to repairing, draught-proofing and replacing period sash windows, from the SashWindow.co team.
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