The latest edition of the building codes (which is quite recent) may dictate deck size based on potential occupancy. All of that will become prevalent during the investigation. The codes are there, the architects/engineers have to follow them as a minimum in their design as well as the constructors (what is in effect at the time of construction). In-depth knowledge and application of these codes are essential in order to be licensed by the State Board as Architects/Engineers. The same goes for contractors doing the construction as an overcheck process and valid qualification of the work being performed. It is the ultimate responsibility of both agencies to remain up to date on all code changes and requirements. It is the ultimate responsibility of the inspectors to ensure that both the design intent and the construction methods are accurately applied and are in compliance to the exist revision of the code manual.
Safety factors are applied after the static and live loading loading requirements are determined which are based on the building codes. Safety factors are not applied to safety factors.
My last causal factor covers the material condition you mention. I did however, neglect to include the potential lack of maintenance or repairs of the structure by the owner.
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