Understanding Ontario plumbing rough-in requirements prevents costly do-overs and failed inspections. This covers OBC drain/waste/vent requirements, supply sizing, and permit obligations for GTA renovation projects.
Ontario Plumbing Code Key Requirements
Drain slope: All horizontal drains must slope minimum 1:50 (2%). Preferred is 1:40 for drains up to 3-inch diameter.
Trap-to-vent distance: Maximum 1,350mm (4.5 ft) for 1.5-inch trap arm. 1,800mm maximum for 2-inch trap arm. Critical constraint for basement bathroom additions.
Stack sizing: 3-inch minimum for toilet connection. 4-inch stack if serving more than one toilet.
Basement Bathroom Addition
Adding a bathroom below the main drain exit typically requires a sewage ejector pump ($2,500-$5,000 installed). Gravity drainage is possible only if the basement floor level is above the municipal sewer connection point.
Full basement bathroom rough-in (toilet, sink, shower): $4,000-$8,000 labour plus materials. Add $3,000-$6,000 for concrete saw-cut and patch.
Supply Pipe Materials
PEX: Most common new installation. Flexible, freeze-resistant, $0.50-$1.50/ft. No lead concerns.
Copper: Traditional, 50+ year lifespan, $2-$5/ft. Required in some commercial applications.
Permit Requirements
All new plumbing installations require a plumbing permit in Ontario. Rough-in inspection required before walls are closed. Budget $150-$400 for GTA permit fees.
Complete guide with diagrams: Ontario Plumbing Rough-In Guide 2026 - Drain, Waste, Vent and Supply Requirements – Telegraph