A roughly 100-page report on factors that caused a ceiling to collapse at the recently-built Harjurinne School in Loviisa was published on Thursday.
Construction of the school was completed in 2014, but last November some 60 square metres of the cafeteria's ceiling collapsed, bringing down piles of rock wool insulation and construction materials onto the floor.
The school was closed at the time and no one was injured by the falling construction materials, but the incident marked the third time that month in which a school ceiling collapsed in Finland.
Skanska, the construction firm that built the school, took responsibility for the incident and vowed to repair it. According to the school that work has recently been completed.
The report, issued on Thursday by the municipality's building inspection department, found there were several reasons behind the collapse, according to Loviisa's senior building inspector, Miia Hento.
"In some parts of the ceiling too many nails were used, up to four in some places, and none of them stayed in place. If you drive in nails that are too close together, they do not hold adequately," Hento said, adding that using several nails in one spot actually has less holding strength than using just one nail in the right spot.
She also said that some of the ceiling's nails were not hammered in the right spots. Some of the ceiling's wood planks had split because nails had been driven into the ends of them but didn't reach other boards.
"The boards were nailed directly into the truss and the whole structure fell down," Hento said.
No matching blueprints
Apart from the nails not being able to hold the ceiling in place, there is the possibility that too much rock wool insulation was used in some part of the structure, according to the report. The amount of insulation may have added pressure to the ceiling's weak points and contributed to its collapse.
During construction of the school, Skanska workers had been working from several different blueprints that did not match each other, according to the report.
"[Drawings of] the pipes and plumbing were included in some of the blueprints but were not in the building plan's sectional drawings. No one created a blueprint that included everything," Hento said.
She said however that the pipes installed along the ceiling are adequately fastened and have not loosened.
The repair work needed after the ceiling collapse is now complete and the cafeteria was opened to students on Monday, according to the school.