If you're replacing a window, installing a shower screen, or adding a glass balustrade, you've probably come across the terms toughened glass and laminated glass. Both are classed as safety glazing, but they're made differently, behave differently when broken, and are suited to different situations. Here's what every NZ homeowner needs to know.
How Toughened Glass Is Made
Toughened glass (also called tempered glass) is standard float glass that has been heated to a very high temperature and then rapidly cooled. This process puts the outer surfaces under compression and the core under tension, making the finished pane several times stronger than ordinary glass of the same thickness.
The key characteristic of toughened glass is how it breaks: when it does fail, it shatters into thousands of small, relatively blunt pebble-like fragments rather than large, sharp shards. This dramatically reduces the risk of serious cuts — which is why it's classified as safety glass.
Important limitation: toughened glass cannot be cut or drilled after it has been processed. All sizing, hole-drilling, and edge work must be done before toughening. If you order the wrong size, the whole pane must be remade.
How Laminated Glass Is Made
Laminated glass is made by bonding two or more panes of glass together with one or more interlayers — typically a tough plastic film called PVB (polyvinyl butyral) or, in higher-spec applications, SGP (SentryGlas). The layers are fused under heat and pressure.
When laminated glass breaks, the fragments stick to the interlayer rather than falling away. The pane may crack and craze, but it generally stays in one piece — much like a car windscreen. This "hold-together" behaviour is its defining safety advantage.
Laminated glass can also be specified with acoustic interlayers to reduce noise transmission, or with UV-filtering interlayers to protect furnishings — useful in sunny, north-facing NZ rooms.
Key Differences at a Glance
| Feature | Toughened Glass | Laminated Glass |
|---|---|---|
| Strength | Very high impact resistance | Moderate (depends on thickness) |
| When broken | Crumbles into small pebbles | Cracks but stays in place |
| Security after breakage | No — opening created immediately | Yes — pane holds together |
| Sound reduction | Minimal | Good (with acoustic interlayer) |
| UV protection | No | Yes (with UV interlayer) |
| Can be cut after manufacture | No | Yes (some types) |
| Typical cost (guide only) | Generally lower | Generally higher |
Where Each Type Is Required in NZ
The NZ Building Code sets out where safety glazing is mandatory. The relevant clauses are Clause F4 (Safety from Falling) and Clause F2 (Hazardous Building Materials), and glazing in critical locations must meet NZS 4223, the New Zealand standard for glazing in buildings.
Toughened glass is commonly specified for:
- Shower screens and wet area enclosures
- Sliding and hinged glass doors
- Low-level windows (where the bottom of the pane is close to floor level)
- Oven and appliance doors
Laminated glass is commonly specified for:
- Overhead glazing (skylights, glass roofs) — because if it breaks, the pane stays in place rather than raining fragments down
- Balustrades and frameless glass barriers — where the glass must continue to provide a barrier even after impact
- Bushfire-prone areas — laminated glass performs better under radiant heat
- Security glazing — intruders cannot quickly clear a broken pane
- Acoustic applications — double glazing with a laminated pane significantly reduces traffic noise
For balustrades in particular, MBIE Building Performance guidance and NZS 4223 generally require laminated glass (or laminated toughened glass) because a balustrade must remain a barrier even when damaged.
Can You Combine Both?
Yes — laminated toughened glass is a thing. The glass is toughened first, then two toughened panes are laminated together. You get the strength and small-fragment breakage of toughened glass combined with the hold-together safety of laminated glass. This is the premium option for balustrades, pool fencing, and overhead glazing where both strength and post-breakage integrity are critical.
NZ Climate Considerations
New Zealand's climate varies enormously — from the humid, salty air of coastal areas to the UV-intense summers of Central Otago and Hawke's Bay. Laminated glass with a UV interlayer can help protect interior furnishings and flooring from fading. In high-wind zones (common in Wellington and exposed coastal sites), your glazier may recommend thicker or laminated units to meet wind-load requirements under NZS 4223.
For double-glazed units (IGUs), either toughened or laminated glass can be used as one or both panes — your glazier will advise based on the location and Building Code requirements. BRANZ has useful guidance on glazing performance in NZ conditions.
When to Call a Professional
Glazing work in critical locations — including balustrades, pool fencing, shower screens, and any glazing covered by the Building Code — should always be installed by a qualified glazier. Incorrect glass specification or installation can result in a failed building inspection or, worse, a serious injury.
While a homeowner can replace a simple like-for-like pane in a low-risk location, any work that involves:
- Structural glazing or balustrades
- Wet areas (showers, bathrooms)
- Overhead glazing
- New openings or alterations requiring a building consent
…should be handled by a professional. You can find qualified local glaziers on tradedirectory.co.nz.
Safety note: Never attempt to handle large glass panes without proper PPE (cut-resistant gloves, safety glasses). Broken glass — even toughened glass pebbles — can cause serious eye and skin injuries.