Double Glazing · Updated August 2026
Blown Window Repair Cost UK 2026: Misted Unit Prices
A blown window — condensation trapped between the panes — means the sealed unit has failed, not the window. Replacing just the glass unit costs £75–£250 fitted for most casements, rising to £200–£450 for toughened patio-door glass. The frames stay put, which is why a unit swap runs at a fraction of the £400–£1,800 a full new window costs.
Blown window repair cost by unit — 2026
Supply and fit, glass unit only — frames, hinges and handles unchanged. Most fitters carry a call-out minimum of £80–£150 that covers the first unit.
| Unit | Typical cost | Time on site | Notes |
|---|---|---|---|
| Small casement unit (to ~0.5m²) | £75–£150 | Under an hour | Top openers, cloakroom windows |
| Standard casement unit | £100–£200 | ~1 hour | The commonest replacement |
| Large fixed / picture unit | £150–£300 | 1–2 hours | Two fitters above ~1.8m² |
| Patio door glass (toughened) | £200–£450 | 1–2 hours | Safety glass is required by regs |
| Bay window (3–5 units) | £300–£850 | Half a day | Per-unit price falls with quantity |
| Whole-house refresh (8–12 units) | £700–£1,900 | A day | Worth batching for the discount |
| “Demisting” (drill and vent) | £60–£120 / unit | Under an hour | Temporary — the seal is still failed |
Indicative 2026 UK prices, compiled from published installer pricing (Checkatrade, MyJobQuote and MyBuilder misted-unit guides, August 2026). Sealed units are made to measure - treat these as a budgeting guide and confirm against written per-unit quotes.
What changes the cost
| Cost factor | Typical impact | Why it matters |
|---|---|---|
| Unit size and shape | the base variable | Sealed units are priced per m2 and made to measure - arched and shaped units cost noticeably more |
| Glass specification | +20–40% | Toughened is compulsory in doors and low-level glazing; low-E (K) glass should match the originals or one pane reads darker |
| Access | +£30–£100 | Upper-floor units needing ladders or towers take longer and sometimes a second visit |
| Quantity | −15–30% per unit | The call-out is spread across the batch - doing one misted unit at a time is the expensive way |
| Frame condition | the replacement signal | If gaskets are perished or frames warped, new glass mists again - that money belongs in full replacement |
Blown window repair cost by UK region — 2026
Modelled from regional labour rates rather than measured in this category - materials cost much the same everywhere, the labour does not.
| Region | Typical installed cost | vs UK average |
|---|---|---|
| London | £120–£270/unit | +25–30% |
| South East | £110–£250/unit | +15–20% |
| South West | £90–£220/unit | +5% |
| Midlands | £90–£210/unit | baseline |
| North England | £80–£190/unit | −5–10% |
| Scotland | £80–£190/unit | −10% |
| Wales | £80–£190/unit | −10% |
| Northern Ireland | £80–£180/unit | −15% |
Getting it priced properly
1. Count and photograph every misted unit
Fitters price per unit and discount by quantity. One phone photo per window is enough for a firm per-unit quote.
2. Get the glass spec in writing
Toughened where regulations require it, low-E to match the originals, and trickle-vent or Georgian-bar details noted - the quote should name them all.
3. Check the frames before you spend
Press the gaskets and check corners for warp. Sound frames make a unit swap the obvious win; failing frames mean new glass will mist again.
What blown window repairs cost - 2026
Every figure comes from the cost table above.
Blown window repair — frequently asked questions
A double-glazed sealed unit whose edge seal has failed. The desiccant in the spacer bar saturates, moisture creeps between the panes and shows as misting or droplets you cannot wipe off. The glass unit needs replacing; the window itself usually does not.
“Demisting” services drill the unit and vent or flush it for £60–£120. It clears the visible mist for a while, but the seal is still failed and the insulating gas is long gone — most units mist again. Treat it as a cosmetic stopgap, not a repair.
When the frames are sound, yes — a unit swap typically costs £75–£250 against £400–£1,800 for a full new window. When gaskets are perished or frames warped, the new unit will fail early and full replacement is the honest advice.
Two visits: one to measure, then about an hour per unit to fit once the made-to-measure units arrive — usually one to two weeks later. Beads are removed, the unit swapped and the window back in use the same hour.
Related glazing guides
When repair stops making sense: full window prices.
A realistic figure for full replacement in 30 seconds.
The national installers compared on price and guarantees.
Reviewed by the BestBuilders editorial team on 12 August 2026 · Next scheduled review: November 2026 · See our editorial standards.