What is Tempered Glass? Why Does California Require It in Tub or Shower Surrounds?


Tempered glass is something that you only appreciate when things go wrong. It’s significantly more expensive than regular (annealed) glass, but a lot cheaper than your hospital bills if you fall through annealed glass. Tempered glass is a kind of safety glass that is five or six times stronger than normal glass. It’s because of this extra strength and other safety attributes that it is required by the California Building Code in bathrooms and other dangerous areas of the house. If you need some tempered glass installed in your bathroom, talk to Tim Hmelar and his team at The Kitchen and Bath Company of Palo Alto.

The main difference between tempered and annealed glass is the way that it is treated. For glass to be tempered, it either needs to undergo a chemical treatment, or it is heated up to well over 1000 ̊F and then rapidly cooled with drafts of air. This process puts the outer surfaces under compression and the inner surfaces under tension. The compressive forces close-up the surface flaws that would have otherwise existed in the glass. Not only does this make the glass stronger, but it also makes it crumble into granular chunks when it does break. These are much less likely to seriously injure a person than the large shards of normal glass.

The only downside of tempered glass apart from the cost is that it cannot be worked once it has been tempered. Any impact, such as cutting or grinding, will cause the glass to fracture. This is why it needs to be the perfect size and shape before it is fired.

Because of the additional strength of tempered glass, it is more resistant to impacts, earthquakes or fires. The California Building Code requires it to be used in many high risk areas, such as in doors, near stairs and wet areas such as bathrooms. The high risk of slipping in bathrooms make tempered glass a necessity to reduce injuries. Any glass in a wet area, where the bottom edge is less than five feet above a standing or walking surface, needs to be made of tempered glass.