GS Engineering and Construction will completely rebuild its apartment complex in Incheon after an underground parking lot collapsed in April due to poor construction.

The apartment complex, being built by GS E&C and developed by Korea Land and Housing Corp. (LH), was set to be completed in October.

GS E&C will tear down and reconstruct 17 apartment buildings for 1,666 households in Geomdan New Town in Incheon. The reconstruction will cost the builder around 500 billion to 1 trillion won ($384 million-$768 million).

The company's decision came with the apartment complex’s future residents calling for the reconstruction, as the collapsed underground parking lot was located between two apartment buildings and beneath a children’s playground. There were no casualties in the collapse.

As the demolition schedule has not been settled, it is estimated that the complex’s move-in period will be pushed back four to five years. Residents were scheduled to start moving in from December this year.

The construction firm’s announcement came after the Ministry of Land, Infrastructure and Transport’s inspection team announced that the apartment complex’s underground parking lot was demolished due to construction failures throughout the project, from its design, superintendence and construction.

On April 29, a slab roof of an apartment complex’s underground parking lot collapsed around 11:25 p.m. The parking lot was located between two apartment buildings.

The ministry established an inspection committee to investigate the accident for two months. The committee concluded that the cause was due to missing steel rebars.

The construction project’s design overlooked the inclusion of steel rebars, which serves the function of connecting the upper and lower reinforcement. Some of the rebars that were included in the design were also not installed. Weight additionally gained during landscaping added pressure on the roof, leading to its collapse.

The inspection team concluded that it was unlikely that the steel rebars were intentionally left out. “Steel rebars’ impact on construction costs is not significant, so it’s hard to say it was intentional,” said Hong Geon-ho, head of the inspection team.

Additionally, the ministry’s inspection team found that the strength of the concrete used for the roof ignored safety standards. According to the standards, the concrete’s strength should be at least 20.4 megapascals. The strength of the concrete taken from the collapse site was around 16.9 megapascals.

LH also was found lacking in checking the quality of materials used during construction. According to the Construction Technology Promotion Act, a developer must conduct quality control checks at least once a year during construction. LH did not conduct quality control checks even once.

The ministry held both GS E&C and LH accountable for the incident and plans to announce disciplinary actions next month. LH also issued an apology and vowed to come up with measures to prevent similar accidents from occurring in the future.