External fire ratings of flat roofs are vital to protect the inhabitants of a building and the people and properties nearby when fire breaks out.
The Building Regulations Part B (Fire Safety) part B4 covers the requirement of the external walls and roof of a building to adequately resist the spread of fire over the walls/roof of the building, and from one building to another.
Section 10 covers roof coverings. In the case of flat roofs, the covering will usually consist of the deck, vapour control layers, insulation, waterproofing membranes, and any other layers and spaces.
The performance of roof “coverings” or build ups, is assessed by the application of tests which produce a rating for that build-up.
The rating or Class consists of two letters, one for each of two tests which correspond with the requirement to prevent a) penetration of fire and b) spread of flame into the building below.
This gives a combined classification from AA to DD, with A being the highest class and D being the lowest.
The tests have been developed to simulate likely situations where there is a fire nearby in a building or on a boundary.
The first of the two letters relates to the Fire Penetration Test.
• “A” means no penetration occurred during the 60-minute penetration test.
• “B” means penetration occurred after 30 minutes;
• “C” means penetration occurred in less than 30 minutes, and
• “D” means penetration occurred during the Preliminary Test.
The second of the two letters relates to the Spread of Flame Test.
• “A” means no spread of flame occurred during the 3-minute spread of flame test.
• “B” means the flame spread less than 533mm during the test;
• “C” means the flame spread more than 533mm during the test, and
• “D” means the product continued to burn for longer than 5 minutes after the pilot flame was removed, or the flame spread was greater than 381mm during the Preliminary Test.
An AA rating therefore means fire penetration has not occurred within an hour of the test commencing and there was no spread of flame.
In comparison, BB means test specimens were penetrated in not less than 30 minutes and the spread of flame was less than 533mm.
SIG’s SIGnature Torch-On System, exclusive to SIG Design & Technology, achieves an AA rating. The SIGnature range is a torch-applied built-up bituminous membrane roofing system. The range was recently awarded the BBA (British Board of Agrément) certification. Each membrane option features an EXT.F.AA fire rated system build up as standard.
SIGnature is manufactured from bitumen membranes using polyester reinforcements with mechanical strength and dimensional stability. The reinforcements are impregnated and then coated with specially formulated SBS (Styrene Butadiene Styrene) modified bitumen or APP modified bitumen.
A cold applied self-adhesive underlay is available, and the option of either torch applied, or self-adhesive aluminium lined vapour control layers accompanied by a full range of insulation and ancillary products ensures a full system warranty.
A choice of different SIGnature Underlays determines the warranty period; which is either 20 years, or 25 years if the underlay is used in conjunction with the SIGnature Fire Rated Cap Sheet.
View SIGnature - torch-applied built up roofing system Product Entry