US officials are today set to confirm that dry rot was the primary cause of the San Francisco balcony collapse which resulted in six students falling to their deaths.
In one case, a timber balcony beam was found to be so degraded by the water-based fungus the wood had been reduced in places to little more than dust.
Other beams were blackened by the fungus with tell-tale white blotches.
Seven other students, all Irish and in San Francisco on J1 student visas, were hurt, two of them with critical injuries, when the fourth-storey balcony failed at 12.41am last Monday.
City of Berkeley officials will release the preliminary findings of their investigation within the next 24 hours.
Overloading has already been ruled out as a cause with the balcony, supported by eight timber joists, designed and built to be capable of handling 1,770kg, or the weight of 25 young men and women.
It has also emerged that two years ago inspections revealed suspected dry rot in an apartment on a floor below that from which the Irish students fell to their deaths. The inspection conducted on September 11, 2013 found evidence of dry rot in an interior floor deck.
The building developers, Segue Construction, insisted the Berkeley incident is totally unrelated to the settlement of construction litigation cases in San Jose and Millbrae, which cost the firm $6.5m.
Both claims were lodged over allegations of water damage to balconies.
Segue is also the focus of an ongoing breach of contract court case which alleges "water intrusion causing tangible property damage" in Colma, California.
The focus of the City of Berkeley probe is now on what caused the dry rot in a building just eight years old.
Central to the probe is a waterproof membrane which, under planning regulations, must be wrapped around supporting timber beams in the so-called 'podium construction' of the Library Gardens complex.
The membrane is designed to protect weight-bearing timber beams from water and from dry rot, which is a significant threat in California.
"The design drawings appear to have called for proper waterproofing," former Brentwood building inspector Lloyd Dinkelspiel said
Last weekend, engineering inspectors acting for the building owners and lease managers, Blackrock and Greystar, began inspections of the properties.
The families of the 13 victims are not understood to have made legal contact with the City of Berkeley or anyone connected with the 160-unit Library Gardens complex.