The report by fire investigation experts BRE Global was leaked to the Evening Standard and reveals deficiencies beyond the flammable cladding panels and insulation.
BRE Global's investigation findings, which emerged yesterday, concluded that the fire would not have spread beyond Flat 16 -- where a single fridge-freezer caught fire -- had the tower's original façade not been reclad.
The fire investigation experts also concluded that refurbishment carried out between 2014 and 2016 had failed, in several fundamental areas, to meet the fire safety standards set out in the building regulations. The 210-page interim report identified gaps around windows, incorrectly fitted cavity barriers meant to stop fire, and dozens of missing or faulty door closers as contributing factors that helped the fire to spread.
Kensington and Chelsea Tenant Management Organisation, the social housing arm of the Royal Borough of Kensington and Chelsea, was the client for the work.
BRE Global's report, dated 31 January 2018, said: "The original façade of Grenfell Tower, comprising exposed concrete and, given its age, likely timber or metal frame windows, would not have provided a medium for fire spread up the external surface. In BRE's opinion -¦ there would have been little opportunity for a fire in a flat of Grenfell Tower to spread to any neighbouring flats."
The fire experts found instead that "deficiencies" in the new façade's construction had provided fuel for fire to spread. Their report identified five significant breaches of the building regulations, which were directly implicated in the loss of life.
Cavity barriers which were intended to expand and seal the gap between the tower's concrete surface and the cladding should a fire occur were of "insufficient size specification". Designed to close a 25 mm gap, the cavity barriers were installed with a 50 mm gap. Some had been installed upside down or back to front, which BRE Global concluded had aided the fire's spread.
The second breach related to the window frames, which were "significantly narrower than the gap between the concrete surfaces of the columns, 150 mm narrower," leaving large spaces at the end.
These gaps were filled with a rubberised membrane, rigid foam insulation and uPVC lightweight plastic panels. However, BRE Global concluded that "none of the materials used would be capable of providing 30 minutes' fire resistance", adding that this allowed "a direct route for fire spread around the window frame into the cavity of the façade -¦ and from the façade back into the flats".
The third and fourth breaches related to the insulation foam used and the aluminium composite material used in the façade, which had a polyethylene (plastic) core. Both were identified as "combustible" and "provided a medium for fire spread".
Finally, the report found that almost half (45%) of the door closers on the 120 flats between the fourth and 24th storeys of the tower were missing or not working. This meant that doors were left open when residents evacuated the building, allowing smoke and fire into the single stairway used to escape the 24-storey, 70m tower.
BRE Global noted that the individual breaches relating to the cladding system assumed far greater importance when "considered in combination as opposed to when they occur in isolation".
The Evening Standard reported that the findings could feed into the public inquiry, which is due to start on 21 May.