Here at The Rooflight Centre, we are often asked about our range of walk-on rooflights for their businesses. But it is often the case that our customers don’t require a walk-on at all, but instead need non-fragile rooflights made of toughened glass.
Non-Fragile & Walk-On Glass: What’s The Difference?
Walk-on rooflights are usually placed on roof terraces over the top of basement rooms, which is why they must be suitable to walk on. But non-fragile rooflights can be used for this same purpose. They are strong enough to prevent a person from falling through the glass should they slip or trip while doing activities on a rooftop.
Non-fragile glass may also be used in areas where footfall could occur but isn’t expected frequently, such as in emergency escape areas in the event of a fire.
Safety Classifications
Non-fragile rooflights and toughened glass must be tested before use by following the guidelines in place set by The Advisory Committee For Roof Safety and the Centre for Window & Cladding Technology respectively
Firstly, ACR(M)001:2005 ensures the inspection of rooflight assemblies along with any additional accessories to ensure the rooflight and its components can support the load of someone stumbling or falling onto the glass.
Secondly, the often relied upon CWCT 66 & 67 deals specifically with glass rooflights and sloped glazing. Depending on the size and specifications of your glass, the results of these tests are likely to differ. To avoid expensive testing, rooflights may be deemed to comply with the CWCT TN92 assuming the framing system has the correct features and recommended glass specifications already in place.
We have categorised these specifications below in simple terms:
Class 0
Is outside the scope of either the TN66 or 67, but the glass is designed to be walked upon in areas like roof terraces where there is a room below.
The upper pane of the toughened glass will either be 25mm, 31.5mm, or 33mm thick, which makes it strong enough to withstand a uniform distributed load of 2500N/m2 for commercial use and a concentrated load of 2000N for domestic use.
This class advises that walk-on rooflights in public or commercial settings should be designed, assessed, and implemented to meet the increased loads associated with higher pedestrian traffic.
Class 1
Class 1 refers to walk-on rooflights that are manufactured to be walked on infrequently for maintenance areas but are not intended for everyday foot traffic.
10mm of toughened glass generally proves robust enough for this purpose during the testing phase. The inner pane of glass should be 9.5 or 11.5mm of annealed laminate depending on the size.
Class 2
Class 2 is the ‘default’ non-fragility classification, as the glass used in this class is designed to prevent a person from falling through them if they were to trip and fall onto the rooflight.
The upper pane of glass can break and is permitted to do so, but the bottom layer mustn’t be displaced from the glazing, else there would be no prevention of someone falling through. Depending on the size, 9.5 or 11.5mm of annealed laminated glass with a 1.5mm PVB interlayer is sufficient in most cases.
Class 3
This class specifies fragile rooflights that should only be installed where there is no risk to anyone and no chance of someone falling through the glass. This is comparatively fragile glass that is blocked off by barriers on flat roof surfaces to prevent anyone from getting close to the rooflight.
In all cases, more economical specifications can be used, providing that testing has been carried out on samples of the same dimensions and glass specifications as the roof glazing is being installed.
The architect who designs any given building should conduct a risk assessment to determine which classification of non-fragile glass is needed.
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Here at The Rooflight Centre, we help to decide which type of glass your rooflight should have. Fortunately, we have a selection of choices suitable for any type of rooflight, from walk-on rooflights to Korniche Roof Lanterns. Contact us now if you’re interested in any of our products! Or email us at rooflights@lonsdalemetal.co.uk.
