What was the cause of the balcony collapsing in the novel, In the Middle of the Night?

It initially appears that the fire may have contributed to the disaster, yet it turns out that the fire had nothing to do with the balcony collapsing. The real cause of the tragedy was structural weakness pinpointed by building inspectors earlier who warned that the balcony was in danger of falling, but their admonitions to fix the balcony were ignored by Mr. Zarbor.