As a 62 unit MF, this might not have been administered out of a residential code. Since the IBC/IRC may not have been used, it is possible it was UBC, or based on the location in the profile, whatever commercial code would have been in use in Canada?? If codes there/then are similar to ours today it could have likely been specified by the designing engineer. But that is all speculation, as we don't know where or what codes were enforced or used, or if an engineer designed it. Either way, as stated, in ICC land they are not mandatory.