Dry rot a possible cause of balcony collapse that killed six in Berkeley
Structural and engineering experts in the US have pointed at dry rot as being the possible cause of the balcony collapse that left six students dead in Berkeley.
Three separate investigations are under way 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.
Mayor Tom Bates said the tragedy was a "wake-up call". He added that city officials planned to inspect 13 other buildings under construction in the city to ensure they are safe.
An Oakland civil engineer, speaking to the San Francisco Chronicle newspaper, said his initial inspection of accident scene photos indicated timber supports were affected by dry rot due to rainwater.
Gene St Onge stressed that while his assessment was preliminary, it appeared to be a classic case of there being inadequate waterproofing at the point where the deck meets the house.
"If the waterproofing is substandard, rainwater can enter the building, causing dry rot, which can destroy the wood members within a short time, - ie only a few years from construction," he said.
Bernard Cuzzillo, a mechanical engineer who owns a Berkeley laboratory and studies why structures fail, came to the scene to view the damage and take photographs.
He said the wood structure of the balcony - which sat beyond a set of French doors - appeared to have been exposed to rain and that the "wood joists were obviously degraded due to dry rot".
He was not involved in the official investigations.
Other experts said the balcony should have been designed to carry a weight of 3,000lbs, and if there were 13 people on it with an average weight of 200lb each (14st 4lbs) then that would equate to 2,600lbs - well within the limits. This increased the focus of the investigations onto structural construction.
However, Berkeley officials would not speculate on what may have caused the balcony to break away.
"In 48 hours we should know more," said Matthai Chakko, a city spokesman.
Carrie Olson, who was on the Berkeley Design Review Committee that approved the building in 2001, said the balcony that collapsed was intended largely as decoration, and was "definitely not large enough to be what the city would call an 'open space balcony', where groups of people could stand outside," according to The San Francisco Chronicle.
It said Olson abstained from the 2001 vote that approved the building.
As the investigation began officials identified three similar balconies at the 177-unit apartment complex out of concern that they might not be structurally sound.
The city officials have ordered the property owner to "perform a structural assessment of the remaining balconies within 48 hours".
Investigations into the tragedy - the third such major US balcony collapse in 12 years - are being carried out 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, tipping the 13 occupants onto the street below.
City of Berkeley spokesman 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," he added.
"The building finished construction in January 2007."
The complex was only built in 2007 and is popular both as accommodation for University of California 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.
Library Gardens, which consists of two buildings, is described on its website as the "premiere choice for convenient Berkeley apartments".