The fire rating of a single ply membrane is determined through standardised testing methods, which take into account the complete flat roof system from the structural deck upwards. There are different fire ratings for construction products depending on what is being tested; for a flat roof system, the resistance of the roof to external fire exposure is usually of most interest.
Tested against the European standard EN 13501-5, the leading flat roofing systems achieve a rating of BROOF(t4), the best available. Tested to the UK national standard BS 476-3, the leading systems achieve a rating of AA, AB or AC (AA being the best, and where the first letter represents the time to penetration and the second letter the spread of flame).
These results can be considered approximately equivalent, but should not be assumed to mean exactly the same thing, since the two test methods are different. The European standard takes precedence as the method to follow and declare to, but the national class test declarations remain in common parlance.
Results of fire testing help to assess the suitability of a roof system against national building regulations, including the distance from adjacent buildings or “relevant boundaries” that the roof system can be used.