The Ontario Building Code | Steel Pipe
7.2.6.7. Steel pipe
(1) Except as provided in Sentences (2) and (3), welded and seamless steel pipe shall not be used in a plumbing system.
(2) Galvanized steel pipe may be used in a drainage system or a venting ="http://thehandyforce.com/interior/bathroom-renovations/" title ="Toronto Bathroom renovation inspiration">venting system above ground inside a building.
(3) Galvanized steel pipe and fittings shall not be used in a water distribution system except,
(a) in buildingsof industrial occupancy, or
(b) for the repair of existing galvanized steel piping systems.
(4) Galvanized steel pipe and fittings shall conform to ASTM A53/A53M, "Pipe, Steel, Black and Hot Dipped, Zinc-Coated Welded and Seamless".
(5) Where galvanized steel pipe is used in a drainage system, it shall be used with drainage fittings.
(6) All steel pipe of 4 in. size and smaller shall be schedule 40 or heavier and fittings of less than 2 in. size shall be galvanized screw fittings.
In Plain Language
Except in specific permitted cases, welded and seamless steel pipe can't be used in a plumbing system, though galvanized steel pipe is specifically permitted in drainage or venting systems under those exceptions.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.