Interesting claim. Wikipedia is unsure but uses the floor count meaning in the article. > The name derives from the maximum permissible five floors of combust

Interesting claim. Wikipedia is unsure but uses the floor count meaning in the article. > The name derives from the maximum permissible five floors of combustible construction (Type III or Type V) over a fire-resistive Type I podium of one floor for "5-over-1" or two floors for "5-over-2", as defined in the United States–based International Building Code (IBC) Section 510.2.[1][4] Some sources instead attribute the name to the wood framing of the upper construction; the IBC uses "Type V" to refer to non-fireproof structures, including those framed with dimensional lumber.[5][6]