The Berkeley apartment balcony that collapsed last week, killing six people and injuring seven, was supported by laminated wooden beams that are considered especially vulnerable to water damage and became “severely dry rotted,” a city inspection report released Tuesday showed.
The balcony directly below the one that gave way during a 21st birthday party for a visiting Irish student at 2020 Kittredge St. was also badly rotted and was condemned as a structural danger, the city said.
City officials said they are seeking new regulations “to enhance the safety of all current and future buildings in Berkeley” in the aftermath of the collapse of the fifth-story balcony early June 16.
They stressed that beyond that, the city’s response to the collapse is at an end.
Berkeley is not conducting an investigation into whether anyone should face criminal charges, officials said. And although outside experts have said that problems during construction could have led to the rapid onset of rot in the 8-year-old building, Berkeley’s report did not go into what allowed the balcony supports to be exposed to moisture.
“Our analysis is complete and we, the city, are not going to be conducting any further investigation,” said Eric Angstadt, the head of planning for Berkeley.
The changes that officials are proposing would subject new balconies and other waterproofed structures in multiunit buildings to more rigorous requirements for materials, inspection and ventilation. The regulations would also require routine inspections for new and existing multiunit buildings within six months after the rules take effect and then once every five years. The inspections would be paid for by building owners.
The city’s Building and Safety Division concluded that the 176-unit Library Gardens apartment complex on Kittredge Street, where five Irish nationals and a Rohnert Park woman died in last week’s collapse, met state building code requirements in effect when it was completed in 2007 and that all mandated inspections had been carried out.
In a memo summarizing the investigation, the manager of the Building and Safety Division, Alex Roshal, wrote that the balcony that collapsed and the one beneath it had been designed and constructed in the same way.
Both were supported at the bottom by stucco-covered laminated wood beams that held a layer of an engineered wood product called oriented-strand board. The beams and board were topped by a waterproof membrane and undefined “base sheet material,” Roshal wrote. That material was then covered by two inches of concrete.
Laminated beams are subject to more stringent water-exposure restrictions than traditional lumber, Roshal said in his memo. Experts say that is because they are more vulnerable to damage and rot from moisture.
Oriented-strand board is also considered more prone to water damage than traditional plywood. Plywood was the material called for in the building’s architectural plans. Although the finding was cited in Roshal’s memo, city officials at a news conference said they were not aware of any deviation from the plan.
Independent experts who have examined close-up photos of the damage for The Chronicle have said the waterproofing material on the collapsed deck appeared to have been punctured, possibly during construction. However, Roshal’s memo does not say how the water reached the balcony supports, and Angstadt said at the news conference that officials would not look further into it.
“We’re not making any sort of formal causal determination,” he said. “It’s outside the scope of the building inspector’s duties.
“What our observations were is that there was severe deterioration of the wooden structural members, the most likely cause of that deterioration was dry rot, and the most likely contributor to dry rot is moisture infiltration,“ Angstadt said.
“So we don’t know and we’re not going to know or determine how the moisture got into the assembly,“ he said, adding that the city’s plan is to keep water out of“closed assemblies in the future.“
Onne Broek, a forensic inspector who checks buildings for water damage in litigation cases, said engineered lumber such as that used in the collapsed balcony is composed of individual“flaked“ strands pressed and glued together to form strong, stable support joints and beams.
“When you get water, because it’s a wood fiber material, it wants to go back to its original shape,“ Broek said.“It will start falling apart. We’ve seen laminated strand lumber decaying in less than three years.“
If the material becomes too wet, Broek said,“you will start seeing decay very rapidly.“
Roshal said that neither the deck that collapsed nor the condemned one beneath it had air vents. Some experts say such vents could have enabled the deck beams to dry out when they were exposed to water. Roshal noted that city building codes did not require such vents.
Angstadt said building officials would ask the Berkeley City Council to call for pressure-treated wood or galvanized steel for use on balconies in multi-unit buildings, instead of relying on moisture-proof membranes to prevent damage. Owners would be required to pay for inspections that would look for evidence of dry rot on existing buildings.
Any such recommendations would have to go before the state building standards commission for ratification, Angstadt said.“These are the requirements that the building officials think would do the most likely to minimize the chance of this happening again,“ he said.
The Kittredge Street building has two other balconies, neither of which used the cantilevered support system found in the failed decks. Both the surviving balconies were free of water damage, Roshal said.