The test and classification for non-fragility is detailed in a the ACR[M]001 ‘Red Book’. Broadly speaking, the highest classification for most roof assemblies will be Class B. It is a classification for the whole roof assembly irrespective of the presence of a rooflight, so a rooflight cannot have a better classification than the roof it is fitted into. Class A is only achievable if no element of the roof assembly is damaged during the ACR test – something that is generally only possible with roof constructions designed to resist high impact loadings such as those with concrete decks and rooflights designed for floor type loadings. For more information on this subject, check out the ‘Non-Fragility’ section of our technical manual.