Ever wondered what makes some glass safer than others? It’s not just about thickness or quality — it’s about how the glass is made. Tempered glass, also known as toughened glass, is designed to reduce the risk of injury by breaking into small, blunt fragments rather than sharp, dangerous shards.
Knowing whether your glass is tempered is important not just for peace of mind, but for safety and compliance. In the UK, building regulations require safety glass in certain high-risk areas, like doors and low-level windows. Here’s how to tell if the glass in your home meets those standards.
Key Takeaways
- Tempered glass is required by UK Building Regulations in specific locations like doors, low windows, and side panels near doors for safety reasons.
- You can identify tempered glass through its permanent stamp, distinctive stress patterns visible through polarised sunglasses, smooth edges, and subtle surface characteristics.
- The use of safety glass, like tempered glass, has dramatically reduced glass-related injuries, with hospital attendances dropping from 210,000 annually in the 1980s.
What Is Tempered Glass and Why Does It Matter?
Tempered glass, also known as toughened glass, is specially treated to be stronger and safer than regular glass. The manufacturing process involves heating the glass to around 600°C and then rapidly cooling it. This creates a compressed outer layer and tensile stress in the centre.
The result? Glass that’s about five times stronger than standard annealed glass.
The key differences between tempered and regular glass are:
But why does it matter whether your glass is tempered or not?
Safety Benefits
The most important reason is safety. When tempered glass breaks, it shatters into small, relatively harmless cube-shaped pieces rather than sharp, dangerous shards.
This significantly reduces injury risk.
UK hospital statistics tell the story. In the early 1980s, glass injuries accounted for approximately 210,000 hospital visits annually.
More recent data shows childhood injuries from playground glazing at around 40,000 per year, with the decline linked to increased use of safety glass.
That’s a lot of prevented injuries.
Legal Requirements
In the UK, building regulations require safety glass in specific “critical locations”: Part K of the Building Regulations addresses safety glass requirements. Tempered glass must comply with BS EN 12150-1 standard.
- Glazing within 800 mm of floor level
- Glazing within 300 mm of a door edge and below 1500 mm
- Any door glazing below 1500 mm
Compliance is typically demonstrated through FENSA certificates or local authority inspection in England and Wales.
Visual Methods to Identify Tempered Glass
Let’s look at how you can spot tempered glass through simple visual inspection.
Look for the Permanent Stamp
The easiest way to identify tempered glass is to find the permanent stamp. Section 7 of BS 6262-4:2005 requires the mark to be permanently marked with:
- BS EN 12150 or older BS 6206 classification mark
- CE mark or (from 2025) UKCA logo
- The manufacturer’s details
- Year of manufacture
This stamp is typically found in one corner of the glass panel.
No stamp visible? Don’t worry. There are other ways to check.
Examine the Edges
Tempered glass has distinctive edges. Look for smooth, slightly rounded edges that appear fire-polished.
Regular annealed glass typically has sharper, less finished edges.
This test works best on glass that’s not installed in a frame, as the edges are often hidden once fitted.
Surface Characteristics
Toughened glass often shows a faint surface wave known as “roller wave” distortion. This becomes visible when light reflects across the surface at certain angles.
Try this: Look at reflections in the glass under good lighting. If they appear slightly wavy or distorted, that’s a clue the glass might be tempered.
Testing Methods for Identifying Tempered Glass
Beyond visual inspection, there are several tests you can perform to find out if the glass is tempered.
The Polarised Light Test
This is perhaps the most reliable DIY test. Tempering creates internal stress patterns that become visible when viewed through polarised light.
Here’s how to do it:
- Get a pair of polarised sunglasses
- Look through the sunglasses at the glass
- Rotate the sunglasses or change your viewing angle
- Look for dark stripes or rainbow “zebra” patterns
These patterns appear because of the stress distribution within tempered glass. Regular glass won’t show these patterns.
No polarised sunglasses? You can also use your phone’s LCD screen. Place it behind the glass and look through both.
Breakage Pattern Test
Important: This method is for reference only. Never break glass on purpose just to identify it — it’s dangerous and unnecessary.
If glass happens to break, tempered glass will shatter into small cubes approximately 6-10 mm across. Regular glass breaks into large, sharp, irregular shards.
This difference is the key safety feature of tempered glass.
Professional Verification Methods
For absolute certainty, professionals use specialised equipment:
- Table-top polariscopes that map residual stress (from £300)
- Heat-soak testing subjects the glass to 290°C for 2 hours to test durability
- Impact compliance tests for certification purposes
| Verification Method | DIY Friendly? | Reliability | Notes |
|---|---|---|---|
| Permanent stamp | Yes | Very high | Easiest method, but the stamps can wear off |
| Polarised light test | Yes | High | Requires polarised sunglasses |
| Edge examination | Yes | Medium | Some regular glass may have finished edges |
| Professional polariscope | No | Very high | Definitive but requires a specialist |
| Breakage pattern | No! | High | NEVER break the glass to test! |
Conclusion
Identifying tempered glass is straightforward once you know what to look for. The certification mark is your most reliable indicator, but the polarised light test offers a great DIY alternative.
Taking time to verify your glass type isn’t just about ticking a regulatory box. It’s about ensuring the safety of everyone in your home or building.
With glass-related injuries historically numbering in the hundreds of thousands annually in the UK, it’s a small effort for significant peace of mind.
Remember, when in doubt, consult a professional glazier who can provide expert assessment and documentation of your glass type.
Frequently Asked Questions
Do I legally need tempered glass in my house?
Yes, in those "critical locations" defined in Part K of the Building Regulations. Safety glass can be either tempered or laminated, but most installations use tempered glass. Non-compliance could affect home insurance and property sales.
How can I test my glass without removing it?
Check for a BS EN 12150 or CE/UKCA stamp. If you can't find one, use the polarised sunglasses test to look for stress patterns. For definitive results, consult a professional glazier with a polariscope.
Is laminated glass the same as tempered?
No. Laminated glass sandwiches a plastic interlayer between glass panes and holds together when broken. It satisfies safety glass requirements but doesn't have the dice-like breakage pattern of tempered glass. Markings will show BS EN 14449 instead of BS EN 12150.
Can tempered glass be cut or drilled after production?
No. Once glass has been tempered, it cannot be cut, drilled, or otherwise modified without causing it to shatter. All cutting, drilling, and edge work must be done before the tempering process.
