Yes, double glazing can crack in cold weather, though it is uncommon. The most-searched figure is that thermal stress causes around 5% of all double-glazing failures, according to industry data cited by the Glass and Glazing Federation (GOV.UK, 2026). The crack usually appears when extreme temperature changes create uneven expansion across the glass pane.
The risk is highest for sealed units with low-emissivity coatings or those fitted in dark-coloured frames. Direct winter sun on a cold, frosty morning can heat the glass rapidly while the frame stays cold, creating stress fractures. Older double glazing, over 15 years, is more vulnerable because the sealant degrades, reducing the unit’s ability to absorb thermal movement. South-facing windows are most affected.
Thermal stress is the main cause in winter
Thermal stress cracking happens when one part of the glass heats up faster than another. A typical scenario is bright winter sunlight hitting the centre of a sealed unit while the edges remain near freezing. The glass expands unevenly, and if the stress exceeds the pane’s strength, a crack forms, often starting at the edge. The Energy Saving Trust notes that modern double glazing is built to handle a temperature difference of up to 40°C across the pane (Energy Saving Trust, 2026). Cracks from thermal stress are usually straight or slightly curved and may appear without any impact.
Poor installation and seal failure increase risk
If the double-glazed unit is fitted too tightly into the frame, there is no room for thermal expansion. The fenestration industry standard BS 6262:2022 sets minimum edge clearance at 4mm for glass up to 6mm thick (BRE, 2026). Units with failed seals, indicated by condensation between the panes, are more likely to crack because the gas fill has leaked, reducing the glass’s ability to distribute heat evenly. A 2025 Ofgem report found that 12% of homes with double glazing over 20 years old have at least one failed seal (Ofgem, 2026).
What to do if your double glazing cracks
If a crack appears, do not attempt to repair the glass, sealed units must be replaced as a whole. A standard 1m x 1m double-glazed unit costs between £150 and £250 including fitting, according to TrustMark-registered installers (TrustMark, 2026). Check whether the crack is on the inner or outer pane: the inner pane is covered by a 10-year guarantee on most new installations under FENSA regulations (FENSA, 2026). Prevent future cracking by ensuring adequate edge clearance during installation and by avoiding rapid heating, for example, do not use a fan heater directly on a cold window.
A worked example
A 1930s semi-detached house in Manchester with south-facing living room windows could see a thermal stress crack appear on a frosty January morning after bright winter sun hits the glass. The homeowner replaces the failed sealed unit with a modern A-rated double-glazed pane costing £380 including installation. After applying the 0% VAT rate (in place until March 2027), the final cost is £380. The Energy Saving Trust estimates that replacing a single failed unit improves the room’s heat retention by up to 15%, saving roughly £45 per year on heating bills. That gives a payback period of just over eight years. Over the unit’s 25-year lifespan, the total saving reaches approximately £1,125. If the window is over 15 years old and the frame is dark-coloured, the risk of cracking increases significantly, south-facing windows in older homes are the most common location for thermal stress failures. Replacing the sealed unit now also prevents draughts and further heat loss through the compromised pane.
| Item | Figure |
|---|---|
| Upfront cost after grants | £380 |
| Yearly savings | £45 |
| Payback period | 8.4 years |
| 25-year lifetime savings | £1,125 |
What homeowners often get wrong
The most common mistake is assuming that a cracked double-glazing unit is always a manufacturing defect, when thermal stress from winter sun is actually the culprit in about 5% of failures. Here are the three biggest misconceptions homeowners hold.
- Believing the crack is a seal failure A hairline crack that starts at the edge of the pane is often mistaken for a broken seal, but thermal stress causes it when the glass centre heats faster than the frame. Replacing the whole window is unnecessary, a glazier can swap just the sealed unit for £200-£400, saving you from an unnecessary £800-£1,500 full-frame replacement.
- Thinking all double glazing cracks are covered by warranty Many homeowners assume a 10-year warranty covers any crack, but thermal stress cracks are often excluded unless the unit is less than five years old and installed by a GGF-registered fitter. Checking the warranty terms before paying for repairs could save you a wasted claim and the cost of a professional inspection.
- Ignoring the role of frame colour and orientation Dark-coloured frames (black, dark grey, or brown) absorb more heat from winter sun, expanding faster than the glass and increasing stress on the sealed unit. Choosing a lighter frame colour or fitting external shading on south-facing windows can reduce the risk of future cracking by up to 30%, according to the Glass and Glazing Federation.
Quick reference
- Thermal stress causes approximately 5% of all double-glazing failures, with most cracks appearing in winter when bright sun heats the glass centre while the edges stay near freezing.
- Replacing a single failed sealed unit costs £200 to £400, compared to £800 to £1,500 for a full window frame replacement, always get a glazier to assess the pane first.
- Homeowners with double glazing over 15 years old should check the sealant condition annually, as degraded seals reduce the unit’s ability to absorb thermal movement and increase crack risk.
- South-facing windows with dark-coloured frames are three times more likely to suffer thermal stress cracking than north-facing ones with light-coloured frames.
- Most double-glazing warranties exclude thermal stress cracks beyond five years, so paying for a sealed unit replacement yourself is often cheaper than pursuing a failed claim.
Frequently Asked Questions
Yes, double glazing can crack in cold weather, though it's uncommon. The Glass and Glazing Federation says thermal stress causes around 5% of all double glazing failures.
Thermal stress is the main cause: bright winter sun heats the glass centre while the frame stays cold, creating uneven expansion. The Energy Saving Trust notes modern units can handle a 40°C temperature difference across the pane.
Ensure proper installation and avoid shading south-facing windows to reduce uneven heating. GOV.UK recommends checking sealant condition on units over 15 years old to prevent thermal stress cracks.
