No, you cannot cut tempered glass with a glass cutter — and attempting to do so is both dangerous and ineffective. Tempered (toughened) glass is specifically engineered to shatter into small, relatively harmless pebbles when broken, which means any attempt to score and snap it will cause the entire pane to explode rather than cut cleanly. This is a fundamental property of the glass itself, not a limitation of your tools or technique.
Why Tempered Glass Cannot Be Cut
Ordinary annealed glass is cut by scoring the surface with a hardened wheel, then applying controlled pressure to snap it along the score line. This works because annealed glass has no internal stress.
Tempered glass is made by heating annealed glass to around 620°C and then rapidly cooling it. This process creates a layer of high compressive stress on the outer surfaces and tensile stress in the core. The result is glass that is roughly four to five times stronger than ordinary glass — but that stored energy means any significant nick, score, or chip to the surface will cause the entire pane to shatter instantly into thousands of small fragments.
There is no DIY workaround. No special glass cutter, no slow scoring technique, and no home tool will allow you to cut tempered glass to size. It simply cannot be done once the tempering process is complete.
How to Identify Tempered Glass
Before you do anything, confirm whether the glass you're dealing with is actually tempered. Look for:
- A permanent etched or printed mark in one corner — usually showing the manufacturer's name, the standard (such as AS/NZS 2208), and the word "toughened" or "tempered"
- Use in safety-critical locations — under the NZ Building Code (in particular Clause F4: Safety from Falling and Clause G12), tempered or laminated safety glass is required in shower screens, low-level glazing, doors, sidelights, and other hazardous locations
- A slight iridescent sheen or faint distortion visible when viewed at an angle in polarised light
If you're unsure, treat the glass as tempered and consult a glazier.
What Are Your Actual Options?
If you need a piece of tempered glass in a specific size or shape, here are the legitimate paths forward:
1. Order Custom-Cut Tempered Glass
Tempered glass must be cut to size before the tempering process, then tempered as a finished piece. A professional glazier or glass supplier can manufacture a pane to your exact dimensions. This is the standard approach for shower screens, splashbacks, balustrades, and door panels.
2. Replace Like-for-Like
If a tempered pane has broken or you need a replacement, a glazier can measure up and supply a correctly sized replacement. Always use a qualified glazier for safety-critical glazing — see Licensed Building Practitioners for guidance on when licensed work is required.
3. Consider an Alternative Glass Type
For some applications, laminated glass may be suitable. Laminated glass can be cut (with the right tools and experience), though this is still a job best left to a professional glazier.
Safety Risks of Attempting to Cut Tempered Glass
If you attempt to score tempered glass, the pane is very likely to shatter suddenly and without warning. The risks include:
- Serious lacerations from flying glass fragments
- Eye injury — always wear safety glasses around glass, even when just handling it
- Injury to bystanders nearby when the pane lets go
WorkSafe NZ provides guidance on working safely with glass and managing the hazards of broken glazing. Even disposing of a shattered tempered pane requires care — wrap fragments in thick cardboard or newspaper before placing in your general waste bin.
NZ Building Code and Safety Glazing Requirements
In New Zealand, safety glazing requirements are set out under the NZ Building Code. Glazing in hazardous locations — including shower enclosures, doors, sidelights, low-level windows, and balustrades — must comply with AS/NZS 2208: Safety Glazing Materials in Buildings. Using the wrong type of glass in these locations is a Building Code compliance issue and could affect your home insurance.
If you're replacing glazing in a safety-critical location, check with your local council whether a building consent is required. Many like-for-like glass replacements fall under Schedule 1 exemptions, but it pays to confirm — requirements can vary. See MBIE Building Performance for more information on consents and exemptions.
What a Homeowner Can Safely Do
- Measure up the opening carefully and note the glass type before calling a supplier
- Remove broken glass safely using thick gloves, safety glasses, and sturdy footwear
- Temporarily board up a broken opening with plywood to secure the home
- Source quotes from local glaziers
Cutting, drilling, or otherwise modifying tempered glass is not a homeowner DIY task — full stop.
When to Call a Professional
Call a qualified glazier whenever you need:
- A custom-sized tempered or laminated glass pane
- Replacement glazing in a shower, door, balustrade, or other safety-critical location
- Advice on which glass type meets the NZ Building Code for your specific situation
- Removal and disposal of a large broken pane
A professional glazier has the equipment, knowledge, and supplier relationships to get the right glass made to size safely and to code. You can find qualified local glaziers on tradedirectory.co.nz.
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