Last month's disaster killed more than 1,100 workers and highlighted the hazardous working conditions in Bangladesh's $20 billion garment industry and the lack of safety for millions of workers who are paid as low as $38 a month.
"The owner used extremely poor quality iron rods and cement," committee head Khandker Mainuddin Ahmed told The Associated Press a day after submitting the report to the government. "There were a series of irregularities."
The report found that building owner Sohel Rana had permission to build a six-story structure and added two floors illegally so he could rent them out to garment factories. Past statements from authorities said the owner had permission for a five-story structure and added three floors illegally.
The report also said the building was not built for industrial use and the weight of the heavy garment factory machinery and their vibrations contributed to the building collapse. Those factors had previously been cited.
The ground on which the building was built was not fit for a multi-story building, the report said.
"A portion of the building was constructed on land which had been a body of water before and was filled with rubbish," Ahmed said.
The committee recommended that Rana and the owners of the garment factories be sentenced to life in jail if they are found guilty of violating building codes.
Rana, three engineers and four factory owners have been arrested.
The building was shut down briefly after workers spotted cracks in its walls and pillars a day before the April 24 collapse. But the garment factory workers were called back to work, many of them forcefully.
More than 2,500 people were rescued shortly after the disaster. The committee urged the government to ensure that all those injured receive free medical treatment.