Updated guidance on rooflight non-fragility classifications from NARM

  • 24 Aug 2021

NARM, the National Association of Rooflight Manufacturers, has published an updated version of its Quickguide 08. It is entitled ‘Understanding CWCT Classifications of Rooflight Types’.

The CWCT (Centre for Window & Cladding Technology) tests for non-fragility comprise of soft body and hard body impact tests as well as a load retention test.

They are intended to identify what glass size and type of rooflight can be deemed safe for anyone that might be working on or adjacent to the glass from outside as well as protect anyone that may be below the glass. 


There are four classifications assigned by the CWCT standards, these are classes 0, 1, 2 & 3. Simple descriptions of the classifications and applications relevant to them are provided in the document.

Stuart Middle, NARM’s Technical Committee Chairman, comments: “Recent developments in glass rooflight design, including the rise in popularity of so-called ‘walk-on’ rooflights, have led to a degree of confusion around their specification.

“This document has been produced to provide a quick overview to help specifiers avoid potentially dangerous mistakes.”

NARM Quickguide 08 is available from the NARM website. This also hosts a wide range of other technical documents covering different aspects of rooflight specification.

Download a free copy of the document here

For further information, visit

For further information, please contact NARM using the contact details on our website, where you will be directed to the appropriate person.

Visit NARM's website

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