The findings could open the door for legal claims by victims' families.
Brian Kennedy, whose wife Faye died in the CTV building collapse, said that family members would first likely want to hear from the designers, builders and inspectors at the inquiry and then "take it from there."
He said the report helps give him at least some sense of closure.
"It gives me a feeling that I understand exactly what happened, how quick it happened, and that thank god it didn't happen to other buildings," he told The Associated Press.
The department concluded that load-bearing concrete columns were reinforced with insufficient steel, making them brittle, and that the columns' asymmetrical layout made the building twist during the quake, placing extra strain on those columns.
The report didn't specify who was to blame for the shortcomings - the architects who designed the structure, the construction company who built it, or the officials who inspected it. An ongoing inquiry into the earthquake may find some more answers to those questions.
The department has handed its report to New Zealand police, for them to determine whether there is any criminal culpability.
Alan Reay Consultants, which carried out the building's initial structural design, disagreed with the report.
"Personally I feel incredibly torn," Reay said in a statement, issued immediately after the report came out. "I have huge empathy for the families waiting for answers, but these reports are technically inadequate ... Some of the assumptions made in the reports are highly questionable."