No idea, but the rule is a 2 staircase requirement. All building 2 floors and higher in most of Canada and US must require 2 staircases which means that they take up more room in a building and limit the possible room configurations in the building as well. The reason for 2 staircases is because of the increased fire hazards US and Canadian homes faced due to using wood for home construction unlike in Europe where extremely fire resistant materials are used. The host indicates that fire deaths have dropped significantly because of fire retardant technology throughout US and Canadian homes that makes the 2 story rule pointless for home less than 6 stories tall.