A leaked interim report for the Metropolitan Police offers the most detailed assessment yet of the failures in the refurbishment of the building.
It concludes that the fire would not have spread beyond flat 16 on the fourth floor and would not have claimed even a single life if the original facade of the building had not been over-clad between 2014 and 2016.
Parts of the building were also close to collapse at the height of the blaze, but thicker than presently required floor slabs and columns appeared to have saved the building.
According to the London Evening Standard, which has seen a leaked copy of the draft report produced by experts at BRE Global, the refurbishment of the building failed to meet fire safety standards on several counts.
There were gaps of 15cm between the window frames and concrete columns. These were plugged with a rubberised membrane, rigid foam insulation and uPVC lightweight plastic panels, the paper reported.
These materials provided a fuel that allowed the fire originally to spread to the facade and later penetrate other flats as it spread up the exterior of the building.
Cavity barriers failed to seal the void between the original concrete building fabric and the external aluminium composite material cladding during the fire. These fire blocks were often too small, or incorrectly installed found investigators.
This allowed fire to spread rapidly through a chimney effect, particularly up exterior column lines.
The BRE report also finds insulation fitted to the outside of the building was combustible, allowing fire to spread up and across sections of the facade.
ACM cladding panels had flammable polyethylene or plastic cores this allowed fire to spread upwards and across the building ,with burning droplets of polyethylene also falling and igniting combustible materials below.
Taken together the failings in the cladding system proved of greater significance taken together than in isolation.
The report also identifies a lack on door closers which meant that as tenants fled many were left open allowing smoke and fire to spread through corridors, impacting on residents escape down the single stairwell.
It also says that Grenfell should have been fitted with a wet riser main to aid firefighting rather than a dry riser and only enough room around the building for single fire engine to get close to supply water.
The report has not explicitly concluded whether the design or installation was at fault and whether works were approved or inspected.