Non-Fragile & Walk-On Rooflights: What You Need to Know

At the Rooflight Centre, we are often asked about our range of walk-on rooflights, when in fact the building in question would only require a non-fragile, ‘man-safe’ glass.

an image of ecogard rooflights

Non-Fragile & Walk-On Glass: What’s The Difference?

Walk-on rooflights are manufactured with areas like roof terraces or over the top of basement rooms in mind, which means that they are designed to be walked across at frequent intervals.

Non-fragile rooflights on the other hand, are designed to be strong enough to prevent someone from falling through the glass should they slip or trip whilst carrying out maintenance or other activities on a rooftop. The non-fragile glass may also be used in areas where footfall could occur but isn’t expected on a frequent basis, such as in emergency escape areas in the event of a fire.

Safety Classifications

There are two different testing procedures undertaken by The Advisory Committee For Roof Safety and the Centre for Window & Cladding Technology respectively.

Firstly ACR(M)001:2005 inspects rooflight assemblies along with any accessories to ensure the installation and its components can support the load should someone stumble or fall onto the glass.

Secondly, the often relied upon CWCT 66 & 67 deals specifically in glass rooflights and sloped glazing.

Different sizes and specifications of glass are likely to offer different results, so to avoid expensive testing, rooflights may be deemed to comply with CWCT TN92 assuming the framing system has the correct features and the recommended glass specifications.

Below, we’ve categorised these and explained them 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 toughened and laminated glass will be either 25mm, 31.5mm or 33mm thick which makes it strong enough to withstand a uniform distributed load of 2500N/m2 and a concentrated load of 2000N for domestic use.

Walk-on rooflights in public or commercial areas should be designed, assessed and implemented to meet with the increased loads associated with higher pedestrian traffic.

Class 1

an image of the annealed laminate glass

Class 1 refers to rooflights that are manufactured to be walked-on infrequently for maintenance areas but are not hardy enough 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 this glass 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, which means that the bottom layer mustn’t be displaced from the glazing system as it wouldn’t prevent 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

 an image of a guard over the rooflight

Are fragile rooflights that should only be installed where there is no risk to anyone and no chance of someone falling through the glass. These are usually protected by barriers on flat roof surfaces to prevent anyone coming into the vicinity.


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 being installed.

Most importantly, the designer of the building should first carry out a risk assessment to determine which classification of non-fragile glass is needed.

For more information about what we’ve covered in this blog, or any of other products give us a call on 020 8801 4221 or drop us an email at