Three separate investigations into the tragic deaths are likely to focus on the possibility that dry rot caused the balcony to collapse.
California planning inspectors have ordered a full review of the building code compliances and the design specifications for the balcony.
An Oakland civil engineer said his initial inspection of accident scene photos indicate timber supports were affected by dry rot due to rainwater.
Gene St Onge said: "This appears to be a classic case of ... dry rot (due to) rainwater."
The building was subject to regulations set in 1998 and the balcony should have held 27kg per square foot. It was built between 2005 and 2007.
Berkeley officials want to clarify precisely why the balcony collapsed. A specialist team of construction experts has been drafted in to investigate the mysterious tragedy.
All balconies at the Library Gardens complex off Kittredge Street in Berkeley, California, have now been 'red-flagged' or closed until further notice.
The complex is popular both as accommodation for University of California (UC) students and for European students working for the summer.
On the Library Gardens website, the complex, with manicured lawns and a landscaped courtyard, is described as the "premier choice for convenient Berkeley apartments." Units rent for $2,150 to $4,000 (€1,900 to €3,500) a month.
It is located just 5km from UC's Berkeley campus and is also close to the popular Fisherman's Wharf area, where many Irish students obtain summer work. The complex is owned by a Texas-based firm that manages 400,000 apartments across the US.
Greystar, the property management company that oversees the apartment complex, issued a statement last night in which it said "our hearts go out to the families and friends of the deceased and those injured in this tragic accident".
It said it has taken "precautionary steps" to limit access to other balconies in the complex while police carry out their investigation.
Investigations into the tragedy - the third such major US balcony collapse in 12 years - are being led by the Berkeley planning inspector, the Berkeley Police Department and the Alameda County Coroner.
Homicide officers were among those at the scene yesterday but none of the probes are being treated as criminal investigations.
A statement from the City of Berkeley last night said it has ordered the property owner to remove the failed balcony and to carry out a structural assessment of the remaining balconies within 48 hours.
"The City will be retaining possession of the collapsed materials...Once the damaged materials are removed from the building, they will be taken to a City facility and will remain under City control," it added.
Inspectors have been inside the apartment and have carried out "up-close, aerial investigation using cranes to examine the damage". Results of their investigation are expected to be known in several days' time.
The Irish consul in San Francisco said that his office would be assisting other Irish who lived in the apartment block to find new accommodation.