Fire safety standards for flat roofs
Even though there isn’t a comprehensive ban on combustibles within roofs, sections of ADB specifically address fire safety in roof structures, for example in the context of passive fire protection through compartmentation.
Compartment structures (including walls and floors) are fire-resistant constructions in buildings designed to delay fire moving between compartments and prevent it from spreading quickly through the rest of the building. Fire-rated compartment elements buy extra time and allow people in other areas of the building better chances of escape.
A roof can contribute to the internal spread of fire where it passes over the heads of compartment walls – which is why it’s vital to address intricate places like junctions. It’s essential to ensure fire cannot spread via the roof build-up or bypass compartments to enter new zones, nor continue penetrating through the roof structure itself.
Section 8.26 of ADB Volume 2 states, “To reduce the risk of fire spreading over the roof from one compartment to another, a 1500mm wide zone of the roof, either side of the wall, should have a covering classified as BROOF(t4), on a substrate or deck of a material rated class A2-s3, d2 or better.”
This means that the substrate – the insulation layer – must achieve a Euroclass reaction-to-fire rating of at least A2, and the roof covering across the wall junction must be classified as BROOF(t4).
A BROOF(t4) rating, however, does not relate to a fire resistance test. This classification only considers how a roof system reacts to external fire exposure when subjected to burning brands, simulated wind and radiant heat – it doesn’t assess how the system behaves in a fully developed fire.
Roof systems containing combustible materials can achieve a BROOF(t4) rating, but running combustible insulation over the head of a fire-rated wall can prove insufficient in a fire.
To de-risk their buildings and simplify their route to compliance, a growing number of designers and developers are specifying non-combustible insulation throughout the whole roof.