The 1,000 page report has been published by inquiry chair Martin Moore-Bick. It presents the findings and recommendations from the first stage of the inquest.
The first phase examined evidence and testimonies of survivors and first responders, establishing a timeline of the night in June 2017 when a fire in a high-rise building killed 71 people, most of whom had become trapped in the smoke-filled tower as fire spread around the external walls.
"There was compelling evidence that the external walls of the building failed to comply with Requirement B4(1) of Schedule 1 to the Building Regulations 2010," said Moore-Bick
"They did not adequately resist the spread of fire having regard to the height, use and position of the building. On the contrary, they actively promoted it."
The Building Act 1984 and the Building Regulations 2010 states that externals walls of buildings should be able to resist the spread of fire, and that alterations made to existing buildings should not make the building noncompliant.
Fire spread to cladding via plastic window frame
Built in 1974 as council housing, Grenfell Tower underwent a multi million pound refurbishment from 2015 to 2016.
Aluminium composite material (ACM) rainscreen panels with a polyethylene core and insulation panels made with polyisocyanurate (PIR) foam were used to create a new exterior wall around the existing reinforced concrete walls.
The fire was in the cladding system before the first firefighters arrived in the kitchen of Flat 16, where the fire started, at 1.14 am on 14 June 2017.
The refurbishment scheme that introduced the cladding system will be examined more thoroughly in the second phase of the inquiry, but experts and survivors testified about the origin and spread of the fire.
"Although it was not originally my intention to reach conclusions in Phase One about the tower’s compliance with the Building Regulations, I can see no good reason why that question should not be determined now so far as it relates to the external facade," said Moore-Brick
"I accept that the construction of the Building Regulations is ultimately a question of law and there is compelling evidence that requirement B4(1) was not met in this case. It would be an affront to common sense to hold otherwise."
Experts concluded that the most likely way the fire got into the cladding was through a hole made when hot smoke from a standard electrical appliance fire made the uPVC window jamb deform.
Combustable insulation materials around the window frame then ignited, experts concluded, before setting fire to the ACM panels.
Unusual spread of fire caused by decorative plastic crown
It took less than 20 minutes for flames to spread vertically up the tower within the ACM rainscreen, fuelled by their cores of polyethylene – a combustible synthetic thermoplastic polymer most commonly used for making plastic bags and packaging.
PIR and phenolic foam in the insulation boards behind the cladding also contributed to the fire rate and spread.
Exposed polyethylene in the decorative crown that topped the tower melted and dripped as it burned, starting additional fires further down the building, which also spread upwards. This was how the fire travelled across all the faces of the building, until the whole tower was burning from the outside in.
Fins of cladding had been fixed at the top of the building on the pre-cast concrete architectural crown. They served no function beyond decoration. As the crown burned it acted like a "linear fuse" spreading the fire horizontally said Luke Bisby, an architecture professor at the University of Edinburgh and expert witness for the report.
Gaps had been deliberately left between the new wall of cladding and insulation, and the old concrete wall, to allow ventilation and any water that got in to dry out. But on the night of the fire this cavity allowed the fire to reach the materials that fuelled it.
Cavity barriers with strips that expand in the event of fire and block the gaps had been installed, but the investigation also found they were poorly fitted and had gaps between them. However, experts said that in a fire where the flames were inside the ACM panels, such as Grenfell Tower, the barriers would have been little use halting the spread of the flames.
The fire on the outside of the building got into the flats when the heat caused the windows to fail. Extractor fans in kitchens deformed and dislodged, also letting the fire in. Some fire doors failed or were propped open.
Construction industry and government fire safety standards will be investigated
A fire that spreads horizontally and can engulf a high-rise building in under three hours is unusual, said Moore-Bick.
"With that in mind, I intend in Phase Two of the Inquiry to examine (among other things) the extent to which the regime for testing materials intended for use in external walls (including thermoplastic polymer materials such as polyethylene) and the regulations governing their use were, and are, adequate to identify and control the potential dangers from downward and horizontal as well as vertical flame spread," he said.
"I shall also examine what was and should have been known, both by those in the construction industry and by those in central government responsible for setting fire safety standards, about the particular dangers posed by thermoplastic polymers."
Cladding manufacturers Arconic and the refurbishment contractor Rydon pushed back against Moore-Brick making a judgement about building regulations at this stage in the report. However, Moore-Brick insisted the evidence that Grenfell Towers walls did not resist the spread of fire was all too obvious.
"I can see no rational basis for contending that the external walls of the building met requirement B4(1), whatever the reason for that might have been," said Moore-Brick. "There is therefore no good reason for deferring to a later report what is no more than a self-evident conclusion."
Next the inquiry will look at how those responsible for the installation of the cladding system and replacement windows – including Arconic, Rydon, and architects Studio E – were satisfied that Grenfell Tower met building regulations.
"I am satisfied that, although many different factors played a part, the principal reason why the flames spread so rapidly up the building was the presence of the ACM panels with polyethylene cores, which had high calorific value, melted and acted as a source of fuel for the growing fire," he said.
Moore-Brick has made no recommendations about cladding yet, but the government has already banned similar cladding materials and buildings with similar systems can now apply for a government fund to help get it removed and replaced.
More lives could have been saved by an early tower evacuation
Although 227 people escaped the tower that night, Moore-Bick's inquiry also said that more lives could have been saved if the decision to evacuate the tower had been made earlier.
The report highlighted how the London Fire Brigade failed to recognise that compartmentalisation had failed and the tower needed to be evacuated. There was no evacuation plan for the tower, and incident commanders had not been trained on how fires on high rise building facades can spread.
If the decision to evacuate had been made between 1.30am and 1.50am, when the stairways were still relatively smoke-free more people could have been saved.
"I am acutely conscious that those who were on duty that evening were faced with an unprecedented situation for which they were not properly prepared and that both personnel and systems were overwhelmed by the scale of the disaster," said Moore-Bick
"It is right to say at the outset that those in the control room and those deployed on the incident ground responded with great courage and dedication in the most harrowing of circumstances."