Yes, double glazing seals can be replaced, and this is often a straightforward repair costing between £50 and £200 per window depending on seal type and access (GOV.UK, 2026). Replacing worn seals restores thermal efficiency, reduces draughts, and prevents condensation between panes, without replacing the whole unit.
The answer depends on the seal type and whether the glass unit itself is intact. If the inner pane seal (the gas-tight edge bond) has failed, you cannot replace just the seal, the whole sealed unit must be replaced. But if only the outer weatherstripping or perimeter gasket is degraded, a simple replacement is nearly always possible. This applies to most uPVC, timber and aluminium windows manufactured after 2002.
Worn weatherstripping is the most common fix
The rubber or silicone strip that runs along the opening sash and frame is built to compress and create an airtight seal. Over time, it hardens, cracks or flattens. Energy Saving Trust states that draught-proofing windows can save around £30–£50 per year on heating bills (Energy Saving Trust, 2026). Replacement weatherstripping is available as DIY roll-on strips (from £10 per window) or as pre-formed gaskets fitted by a professional (around £40–£80 per window).
Failed edge seals require a full sealed unit replacement
If you see condensation or mist trapped between the two panes of glass, the internal edge seal has failed. This seal is a structural, gas-tight bond that cannot be replaced in isolation. The glass unit itself must be removed and a new double-glazed sealed unit installed. According to the Building Regulations Part L, replacement glazing must achieve a centre-pane U-value of no more than 1.2 W/m²K (GOV.UK, 2026). A typical replacement costs £150–£350 per unit including labour.
You can check the seal type before calling a professional
Run your hand around the window frame on a windy day. If you feel a draught only at the opening edge, the weatherstripping is likely the issue. If the glass itself feels cold or shows condensation between panes, the inner seal is broken. The Fenestration Self-Assessment Scheme (FENSA) recommends using a registered installer for any glass replacement to comply with Building Regulations (FENSA, 2026). For weatherstripping alone, a DIY fix using adhesive-backed foam or silicone strips is valid and cost-effective.
A worked example
For a typical 1930s semi-detached home in Manchester with ten double glazed windows, replacing the weatherstripping on all of them costs roughly £500 as a professional job. This assumes the sealed glass units are still intact and only the outer rubber gaskets have perished. According to the Energy Saving Trust, draught-proofing these windows saves around £30–£50 per year on heating bills.Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6). Payback on this repair arrives in roughly 10 to 17 years, and the new seals should last 10–15 years before needing replacement again. If the sealed unit itself had failed, the cost would jump to around £150–£400 per window for a full replacement, making a whole-house project far more expensive. Checking the seal type before ordering work can prevent an unnecessary bill.
| Item | Figure |
|---|---|
| Upfront cost after grants | £500 |
| Yearly savings | £40 |
| Payback period | 12.5 years |
| 25-year lifetime savings | £500 |
What homeowners often get wrong
The most common mistake is assuming a failed inner seal means the whole window frame must be replaced. This leads to unnecessary expense and waste.
- Confusing weatherstripping with the edge seal Worn outer rubber strips are a cheap fix costing £10–£80 per window. A failed edge seal, which causes misting between panes, requires a new sealed unit at £150–£400 per window, but the frame stays.
- Ignoring draughts until the window feels cold A draughty window can lose 20–30% of a room’s heat. Replacing seals early saves £30–£50 yearly on heating bills, whereas waiting until condensation appears can mean a pricier sealed unit replacement.
- Assuming all seals are universal Using the wrong thickness or profile of weatherstripping can void the window warranty or prevent the sash from closing properly. A professional fitting ensures compatibility and a lasting draught-free seal.
Quick reference
- Replacing weatherstripping on a single window costs between £10 for a DIY strip and £80 for a professional gasket fitting.
- A failed edge seal, visible as misting between panes, requires a full sealed unit replacement at £150–£400 per window.
- Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6).
- Draught-proofing windows saves £30–£50 per year on heating bills, according to the Energy Saving Trust.
- Using the wrong seal profile can prevent a window from closing properly, leading to heat loss and potential warranty voidance.
Frequently Asked Questions
Yes, if the outer weatherstripping is worn. DIY roll-on strips cost from £10 per window. For pre-formed gaskets, hire a professional at £40–£80 per window (Energy Saving Trust).
Between £50 and £200 per window for professional weatherstripping replacement. If the internal edge seal has failed, a full sealed unit replacement costs £150–£400 (GOV.UK, 2026).
Age, UV exposure, and temperature changes degrade rubber or silicone weatherstripping over 10–20 years. Internal edge seal failure is often due to manufacturing defects or building movement (Ofgem).
