In my previous two posts (part 1, part 2) I have outlined the two routes offered by the Building Regulations 2010 Approved Document B (Vol. 2) at B4 (‘External Fire Spread’) to meet the statutory requirement that:
The external walls of the building shall adequately resist the spread of fire over the walls…
The first route, also sometimes called Option 1, or the ‘linear option’, is to satisfy the requirements of paragraphs 12.6 to 12.9. With regard to the fire properties of materials used in cladding systems for buildings over 18m in height, the requirements are in brief:
a) 12.6. External surfaces should be UK Class 0 OR European Class B or better. The relevant UK tests are BS 476-7 and BS 476-6. The European tests are EN ISO 11925-2 and EN 13823. All four tests are surface tests.
b) 12.7 Insulation products should be of ‘limited combustibility’. They should pass EITHER the BS 476-11 750º C furnace test OR the EN ISO 1182 750º C furnace test OR the EN ISO 1716 calorific test. These are combustibility tests.
The second route, also sometimes called Option 2, is for the entire cladding system to pass a large-scale test to BS 8414.
I will now describe the fire properties of the main two components used in the cladding system at Grenfell Tower, and discuss whether they could satisfy the Approved Document B4 requirements, through either of these two routes.