New mandatory building inspections introduced in Berkeley, California as a direct result of the tragic balcony collapse which killed six young people and injured seven others have found that almost one in five multi-unit properties in the city had unsafe water damaged balconies, decks or stairwells.

According to a new report from housing authority, the City of Berkeley, at least 402 properties - or 18% - had moisture or water damage that raised significant safety concerns.

However some 28% of the city's multi-unit building owners did not respond to the authority's request to carry out inspections, so the number of those with water-damaged exterior elements could be higher.

The new mandatory inspections were introduced by the authority in the wake of the tragedy last June in an effort by officials to ensure nothing similar could happen again.

The inspections were part of a three-pronged approach to improve safety, along with new restrictions on building design, and new specifications for building materials that were less likely to retain moisture.

The mandatory inspections relate to staircases, decks, balconies and other exterior structures in multi-unit buildings.

A spokesperson for the city of Berkeley said that many of the units that had been found to be unsafe had already been repaired and the remainder were currently underway.

He said that following the tragedy, the Berkeley city authority had "not only worked incredibly hard to investigate the situation" but had also "proposed and implemented a series of measures involving decks, balconies, staircases and other exterior structures to try and prevent such an accident from happening again".

He also said that the new inspections programme introduced because of the tragedy had  "had a direct, dramatic impact on increasing safety for people in Berkeley".

The families of the six deceased and the seven survivors are currently suing 35 companies, through the California courts, for damages.

Separately the Alameda County District Attorney is carrying out a criminal investigation; the results of which are expected in a matter of weeks.