Laminated vs tempered glass for impact rating
For impact-rated glazing the laminated layer does the rating: its PVB or SGP interlayer holds shattered glass in place, which is what the projectile test measures. Tempering strengthens a single pane but turns failure into full breakage, so a tempered-only lite fails the large-missile criterion. Impact lites are built as a laminated core — typically a tempered or heat-strengthened outer pane, the interlayer, and an inner pane — inside an IGU where insulation is wanted.
The impact chain, step by step
A projectile test (ASTM E1996 / Miami-Dade format) hits the lite at speed, then applies positive and negative pressure cycling. The lite passes if the interlayer retains the glass fragments: no hole through which a hand can reach, no opening that fails the pressure cycle. Tempered glass on its own breaks into dice and releases — which is exactly why it is never the whole answer for impact, only one layer of it.
The interlayer is the structural member. Standard PVB holds fragments; SGP (sentry glass) interlayers are stiffer and carry load longer after breakage, which matters on larger lites and on lites that must stay weathertight after a strike.
How the lite is actually built
A typical impact IGU on our schedule is a laminated core within a double-glazed unit: for example a tempered outer pane, the interlayer, a clear or low-E inner pane, the air (or argon) cavity, and a second pane. The outer pane can be tempered or heat-strengthened; the laminated member carries the residual load. Single-pane lites — doors, some skylight positions — use the laminated build on its own, which is why impact doors are heavy and need the matching hardware.
Glass thickness and cavity width follow the test target: the missile size, the wind speed class, and the pressure differential set the build. That is why the data sheet for an impact unit lists the glazing configuration as a whole, not a pane thickness alone.
What it does to the hardware
An impact lite can be two or three times the weight of a clear pane of the same size. The sash follows: multi-point locking on every engagement, reinforced hinges, and on lift-slide systems a bearing that carries the extra mass on the track. When a drawing shows impact glazing on a slider, the quotation should show the upgraded hardware schedule with it — a standard slider rail under a laminated lite is a failure waiting for the first hurricane.
How to specify it on your schedule
- State the test target: missile, wind speed class, and the listing you need (Miami-Dade NOA / FBC for Florida, AS 2208 cyclone for Australia).
- Name the lite type per position: laminated IGU, laminated single, with low-E or solar-control where the schedule calls for it.
- Leave the build to the test report: the exact pane/interlayer/cavity combination is confirmed against the configured unit, and the report ships with the document pack.
Questions
No — it is a layer. Tempering the outer pane of a laminated lite adds strength against the first strike; the interlayer does the retaining.