A series of engineering, construction and council-related errors over 20 years led to the catastrophic collapse of the CTV building in the second major Christchurch earthquake, a Royal Commission has found.
Prime Minister John Key said the commission's report, released this afternoon, made for "grim and sobering reading".
He said the findings would be of little comfort to the friends and families of the 115 people who were killed in the collapse of the six-storey office block - the biggest loss of life in the February 22, 2011 quake.
The Royal Commission concluded that the engineering design of the CTV building was deficient in a number of ways. It should never have been issued with a building permit by the Christchurch City Council in 1986 because it was not built to the standards of the time.
A number of defects occurred during the construction of the office block, which was poorly supervised by the construction manager.
The Royal Commission also found that after the first major quake in September 2010 the CTV building was "green-stickered" by a rapid assessment team and later by three council building officials, none of whom was an engineer.
The report came after the intensive eight-week hearing which heard testimony from more than 80 witnesses, including collapse survivors, eyewitnesses, building designers, architects, engineers, builders, and inspectors.
The report said that principal engineer Alan Reay did not provide adequate supervision to the structural engineer employed to work on the project, David Harding.
Mr Harding was "working beyond his competence" because he had not designed a complex multi-storey structure before, and was inexperienced in the use of a computer modelling program relied on for the design.
As a result, many of the building's features were non-compliant.
Despite the council's buildings engineer Graeme Tapper holding concerns about the structural designs, he signed it off in September 1986.
The commission found that Mr Tapper and his colleagues had been convinced by Dr Reay that their concerns were unfounded.
After the CTV building collapsed, a number of construction defects were found. While the foreman of the construction was found to be competent, his construction manager Gerald Shirtcliff did not carry out proper or regular inspections at the site.
At one point the contruction was not supervised for five months.
Stuctural weaknesses in the building were identified during its sale in 1990, but the remedies may have weakened the building's ability to withstand seismic activity.
The commission also found that after the September 2010 quake, council assessments declared the building safe without expert advice from an engineer.
Commissioners noted that even if an engineer had been present, there was no guarantee the building would have received a yellow sticker, instead of a green sticker.
Government would not give an official response to the latest part of the Royal Commission's investigation until next year. Mr Key said he wanted to release the report to give the families of the dead access to the information as soon as possible.