THREE separate investigations are underway into why a fourth-storey balcony at a relatively-new US apartment complex collapsed.
California planning inspectors have now ordered a full review of the building code compliances and the design specifications for the balcony.
An Oakland civil engineer, speaking to The San Francisco Chronicle, said his initial inspection of accident scene photos indicate timber supports were affected by dry rot due to rainwater.
"This appears to be a classic case of...dry rot (due to) rainwater," Gene St Onge said.
Berkeley officials now want to clarify why the balcony collapsed.
All balconies at the Library Gardens complex off Kittredge Street in Berkeley, California, have been 'red flagged' - or closed - until further notice.
The complex was only built in 2007 and is popular both as accommodation for University of California (UC) students and for European students working for the summer.
The complex is owned by a Texas-based firm which manages over 400,000 apartments across the US.
Investigations into the tragedy - the third such major US balcony collapse in 12 years - are underway by the Berkeley planning inspector, the Berkeley Police Department and the Alameda County Coroner.
However, none of the probes is being treated as criminal investigations.
The fourth-storey balcony collapsed onto the third-floor balcony after its supports failed, throwing the 13 occupants onto the street below.
City of Berkeley spokesman Matthai Chakko said planning inspectors visited the site immediately.
"The balcony for the affected unit, as well as the three other similar balconies in the building, have each been red-tagged, prohibiting access to those areas," he said.
"The city has ordered the property owner to immediately remove the failed balcony and to perform a structural assessment of the remaining balconies within 48 hours.
"The building finished construction in January, 2007."
Berkeley Police officer Ethell Wilson confirmed they had received a report at 12.10am about a party at the property at 2020 Kittredge Street.
However, no unit attended the scene as a formal complaint was not lodged.