Neil McCarthy of the Cotchett Pitre McCarthy law firm in San Francisco also said dry rot was by far the most common cause of balconies collapsing.
His comments to RTÉ Radio came as Berkeley city council released housing inspection documents showing the apartment complex where the six Irish students were thrown to their deaths was twice in breach of regulations because of suspected dry rot in 2013.
Official reports show damage to flooring was discovered in a main hallway in the complex and also within an apartment on the third floor, one floor below where the students had gathered.
The documents record that remedial work was carried out at the two locations and the building was issued with a certificate of compliance in early 2014.
Mr McCarthy said he had worked on six balcony collapse cases in the last 15 years, some resulting in fatalities. “It’s just alarming that this pattern keeps continuing,” he said. He added that there were two frequent causes, number one being dry rot – a common problem with wooden structures in the damp coastal region.
“The second is structural design defect. In this case, based on the photographs, the most likely cause at this stage is dry rot.” Mr McCarthy said balcony collapses were “100% preventable”.
“The purpose of a balcony is to have a group of people out there relaxing enjoying the view,” he said. “With that understanding it is fully incumbent upon the building owner to make sure the building is safe.
“The problem we have in the bay area is that people treat balconies like they are an appendage. A balcony is one of the greatest safety risks to human life in the home and sadly people don’t treat it like it is.” He said official post-construction inspections were “hit and miss” and so the onus was on the property owner to carry out their own safety checks.
“With simple inspections you can detect if there’s rot in a balcony. In two or three years from now there’ll be another story like this because people are simply not vigilant enough in maintaining the safety of their buildings.”
Cousins Ashley Donohoe and Olivia Burke were remembered at a ceremony over the weekend as kind, fun-loving young women who shared a bond of twins even though they grew up an ocean apart – one in California and the other in Ireland.
A bagpipe player led a brief procession of family and friends carrying the coffins into St Joseph Catholic Church in Cotati, where many present at the packed churched wiped away tears.
The Rev Daniel Whelton said that growing up, the girls would dress alike to try to fool their parents into thinking they were twins.
Mr Whelton said Ms Donohoe’s mother told him the two were embracing when they died. “In life they were together and in death they are together,”he said.
The other four victims - Eoghan Culligan, Niccolai Schuster, Lorcan Miller and Eimear Walsh - were mourned at a Friday night vigil in Oakland attended by family members and dozens of their fellow Irish students, including some who saw them in their final moments.
Hearses carried the four metal coffins into St Columba Catholic Church. Family members huddled together in the rectory for about an hour before entering the church for a private viewing.