Why insist on laminated inner panes?
Protection for building users
The primary concern with any overhead glazing is the safety of people beneath it. If a rooflight's inner pane breaks, a laminated construction ensures that glass fragments remain adhered to the interlayer rather than falling and potentially causing injury to building occupants below. In contrast, toughened glass , while stronger than standard glass, shatters into small pieces upon breakage, which can still fall and pose a risk to people underneath.
While British Standards allow for the use of toughened glass in certain circumstances where rooflights are less than 5 metres above floor level (subject to risk assessment), we align with the Rooflight Association's recommendation that inner panes should always be laminated, regardless of height or location.
Non-fragility performance
Beyond protecting those beneath the rooflight, proper specification must also consider maintenance staff and others who may access the roof. A rooflight with appropriate laminated glass can achieve non-fragility classification, meaning it can prevent someone accidentally walking or falling onto it from falling through, even if the glass is already broken or damaged.
It's important to note that non-fragility is measured on the entire roof assembly – the glass specification, the framing system, and how the glass is secured all play vital roles. Not all laminated glass will automatically achieve a non-fragile classification; an enhanced specification may be necessary.
Testing and classification
Industry standards define a clear fragility test sequence that provides a standardized approach to testing glazed roofs, resulting in classifications that help specifiers select the right solution for each application:
- Class 0: Walk-on rooflights with unrestricted access
- Class 1: Can resist substantial impact without fracturing and remains retained by the supporting framework. Once/if fractured, it can resist a static load.
- Class 2: Similar to Class 1 but permitted to break under impact. Still required to withstand a static load after fracture.
- Class 3: No direct standing on glass. Requirement for falling equipment to not penetrate the glass.
The testing takes into consideration both the threat of people falling onto the rooflight (soft body impact test) and tools or equipment falling onto it (hard body impact test), as well as the residual strength of the glazing if the glass breaks (static load test).