(1) Where a storm drainage system is connected to a public combined sewer, a trap shall be installed between any opening in the system and the drain or sewer, except that no trap is required if the opening is the upper end of a leader that terminates,
(a) at a roof that is used only for weather protection,
(b) not less than 1 000 mm above or not less than 3.5 m in any other direction from any air inlet, openable window or door, and
(c) not less than 1 800 mm from a property line.