The Grenfell Tower cladding did not comply with UK building regulations and was the “principal” reason for the fire’s rapid and “profoundly shocking” spread, the inquiry report said.
Once the fire had taken hold of the building’s exterior, it was “inevitable” that it would find its way inside, Sir Martin Moore-Bick said.
The judge said he still found the rapid engulfment of the tower by flames “profoundly shocking” despite having viewed footage many times over.
He concluded that the “principal reason” the flames shot up the building at such speed was the combustible aluminium composite material (ACM) cladding with polyethylene cores which acted as a “source of fuel”.
The decorative crown then furthered its spread, he said.
Corporations involved with the refurbishment of the tower, in which the panels were added, previously urged the public inquiry not to make “premature” findings on the compliance of the building.
They also said the evidence heard in phase one was too provisional and insufficient for the judge to reach any firm conclusions for the spread of fire on the exterior of the building.
Arconic, which supplied the cladding on the outside of the block, said a “confluence of unfortunate circumstances” rather than the “mere presence” of the panels had caused the spread of the west London fire.
Stephen Hockman QC, representing the company, argued that any conclusion on compliance would “plainly” be premature.
But Sir Martin said he saw “no good reason for deferring to a later report what is no more than a self-evident conclusion”.
He said: “In circumstances where Arconic does not, and could not sensibly, dispute the rapidity and extent of the spread of fire over and around the building (and indeed in its closing statement put forward a number of mechanisms by which it says that could have occurred), I can see no rational basis for contending that the external walls of the building met UK requirement B4(1}, whatever the reason for that might have been.”
His findings are expected to be welcomed by survivors, who had called for Sir Martin to conclude that the high-rise was non-compliant with building regulations and that the 24-storey block failed its residents.
The judge continued: “If any of the core participants had put forward a reasoned argument to the effect that the exterior walls of the building complied with requirement B4(1}, the position might be different, but none has sought to do so.
“I think it is right therefore that I should say at this stage that on completion of the main refurbishment the external walls of the building did not comply with requirement B4(1) of Schedule 1 to the Building Regulations.”
The judge said it seems likely that some aspects of the design of the cladding system and shape of the tower contributed to the speed at which the fire raced up the tower.
And he said he also thinks it “more likely than not” that the insulation behind the cladding contributed to the rate and extent of the fire spread.
However, this must be investigated further in phase 2 for him to reach a more definite conclusion.
He said: “I should like to be able to do so, because I think it would be in the public interest to obtain a better understanding of how these materials behave in conjunction with each other when exposed to fire.”