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Non-fragile rooflights are designed to be strong enough to prevent a person from falling through the glass should they slip or trip whilst carrying out maintenance, cleaning or other activities on the rooftop (subject to risk assessment).
The term ‘non-fragile’ indicates that the surface of the rooflight or flat roof window is durable, resilient, and suitable to be trafficked.
However, this is misleading, as non-fragile ratings apply to a broad range of rooflights, each with significant variation in terms of their resistance to impact.

Non-fragile classifications can be applied to polycarbonate, glass and GRP rooflights. However, there are a number of circumstances affecting impact resilience within this category, including the installation method used, and the coating applied to the surface.

The non-fragile classification is applied to rooflights which are considered resistant to impacts from falling objects (or people), and maintain an equivalent level of impact resistance to that maintained across the surface of the roof overall.

Despite the initial non-fragile classification ascribed to a particular rooflight, it’s important to recognise that certain scenarios may affect the level of impact resistance over time. A rooflight which suffers an apparently inconsequential scratch may be subject to UV damage over time, which weakens the fixture and affects resistance to subsequent impact.

Rooflights with a non-fragile classification are assessed according to the roof loading capacity, as opposed to floor loadings; as a result, even non-fragile rooflight fixtures are not recommended to be walked upon. New rooflight installations should always be designed as non-fragile, and be installed using specified components and approved methodology, to maximise the longevity of the non-fragile classification.


CWCT testing for rooflights identifies a rating (Class 1, 2 or 3), according to performance under a standardised assessment.
A specified weight is released in a controlled fall under gravity, at critical points, to monitor impact resistance.
CWCT TN66 & 67 deals specifically in glass rooflights and sloped glazing.

Class 0

Outside the scope of either CWCT TN66 or 67, but the glazing is designed to be walked upon in areas like roof terraces where there is a room below

Class 2

Class 2 is unsuitable for traffic, but resistant to breakage in the event of surface impact.

Class 1

Class 1 is categorised as suitable for infrequent trafficking for brief maintenance or cleaning.

Class 3

Class 3 is a ‘fragile’ classification, requiring additional safety considerations.


Frequently asked.

For glass rooflights and roof windows, what is the safest choice?

A product that has been tested and achieved a Class 1 rating will provide the highest levels of safety for occupants. The product will feature a defined overall glass specification and laminated inner pane/s.

What is laminated glass?

Laminated glass is constructed of two sheets of glass which are bonded together with interlayers to form a permanent bond. If the glass is damaged, these interlayers act like a ‘glue’ to hold the fragments in place ensuring the glass does not break up into large jagged shards or hundreds of little pieces, protecting occupants below. 

Where can I find more information?

CWCT publishes a wide range of advice relating to testing and certification, more information can be found on their website: https://www.cwct.co.uk/