Façade defects · Glass
Glass breakage and toughened glass: causes, risks and repair.
Why toughened glass sometimes shatters with no impact, what else causes glass to crack or mist, and how a glazing audit confirms what glass you have.
| At a glance | |
|---|---|
| What it is | Cracking or shattering of glass, including spontaneous breakage of toughened glass and failed sealed units. |
| Main risk | Glass falling from height, especially from balustrades, rooflights and high-level glazing. |
| Common on | Glazed offices, balconies and atria. |
| Usually spotted by | Building managers, often after a sudden breakage. |
Why glass breaks
Toughened glass is strong, but a tiny nickel sulphide inclusion from manufacture can make it shatter years later with no impact. Heat-soak testing reduces that risk. Glass also cracks from damaged edges, thermal stress where part of a pane is shaded, frame movement and impact, and sealed units fail and mist up as their seals age.
How to recognise it
- A pane shattered into small pieces with a "butterfly" pattern starting mid-pane.
- Cracks running in from an edge.
- Misting or condensation between the panes of a sealed unit.
- Cloudy or bubbled interlayers in laminated glass.
Why it happens
- Nickel sulphide inclusions in toughened glass that was not heat-soaked.
- Edge damage during installation.
- Thermal stress from shading, films or blinds.
- Frame movement or poor setting blocks.
- Age of sealed units.
Why it matters
- Safety. Broken glass can fall, and toughened glass can drop in clumps.
- Balustrades and rooflights are the highest-risk locations.
- Cost. Replacing high-level glass needs access, so planning helps.
How we investigate it
A glazing audit inspects every glazing system and rooflight, operates opening lights and hardware, and uses specialist equipment on site to confirm glass thickness, coatings and whether it is toughened. Findings are checked against the O&M information, including any heat-soak certificates, so each system is described as built.
How it is put right
- Replace broken or failed units.
- Specify heat-soaked toughened or laminated glass where appropriate.
- Interim protection, such as film or netting, over public areas.
- A risk-based inspection programme for high-level glass.
From our investigations
Examples from our own work. Client and building details are withheld.
See our published case studies
What to send us
The address, photos of any broken glass, where it is, and any O&M manuals or glass certificates. Email enquiries@mtconsult.co.uk, use our contact form or call 0800 048 5229. We typically respond within one working day.
Frequently asked questions
Why did toughened glass break on its own?
Often because of a nickel sulphide inclusion. Heat-soak testing during manufacture reduces the risk.
Can you tell what glass we have without the records?
Yes. On-site testing confirms whether glass is toughened, its thickness and its coatings.
Is laminated glass safer overhead?
Usually, because it stays in place when broken. The right choice depends on the location.
Related
Talk to us
Glass breaking unexpectedly?
Our in-house contracting team provides the access and opening-up, so you have one point of contact.