Bathroom rough-in plumbing means installing the supply lines (hot and cold water) and drain/vent pipes that will eventually connect to fixtures (toilet, sink, shower, tub). Rough-in happens after framing, before drywall — when walls are open and pipes are accessible. The work requires precise measurements (fixture rough-in dimensions vary), proper slope on drains (1/4 inch per foot), and code-compliant venting.
This guide is an overview of the work involved. Plumbing permit and licensed plumber are typical for full bathroom rough-in; this is not first-time DIY plumbing.
Before you start
Three things to settle:
1. Fixture rough-in dimensions vary by manufacturer. Toilet drain location: 12 inches from rear wall (typical) or 10/14 inch (older homes). Tub drain: typically 16-18 inches from one end. Shower drain: location per pan choice. Sink supply: typically 22-24 inches above floor; drain: 18 inches above floor. Get manufacturer's spec for each fixture before roughing in.
2. Drain slope and vent location. Drains slope at 1/4 inch per foot (1:48). Each fixture vented within code-specified distance of trap (typically 5-6 ft for 2 inch pipe). Wrong slope or distance: drain doesn't work, traps siphon dry.
3. Permit + inspections mandatory. Plumbing permit required for any new bathroom in Ontario. Inspector verifies rough-in before drywall (rough-in inspection), again after fixtures (final). Without permit: can't legally use, can't sell.
What you'll need
Tools
- PVC saw or pipe cutter
- PEX cutter
- Crimp tool (PEX) or compression wrench (copper)
- Drill with bits
- Tape measure
- Level
- Pencil
Materials
- PVC drain pipes and fittings (1.5 inch, 2 inch, 3 inch as needed)
- PVC primer and cement
- PEX or copper supply pipe (1/2 inch typical)
- PEX fittings (crimp or compression)
- Toilet flange (PVC, matched to drain)
- Tub/shower mixing valve (rough-in body)
- Pipe straps for hanging supply lines
- Insulation for hot water lines
Get fixture spec sheets before roughing in
Every fixture has specific rough-in dimensions. Toilet: 12 inch typical from wall to drain centre, but verify your toilet.
Wrong rough-in = fixture doesn't fit. Re-rough is hours of work.
Manufacturer spec sheets show exact dimensions; print and reference.
Step-by-step instructions
Plan layout based on approved drawings
From bathroom design drawings: locations of toilet, sink, tub, shower.
Reference fixture rough-in specs.
Mark on subfloor or framing where each rough-in connects.
Run main drain to existing main
Connect new drain runs to existing main drain.
Slope: 1/4 inch per foot.
PVC pipe with PVC primer and cement at joints.
Wider pipe for downstream sections (3 inch for toilet drain, 2 inch for sink/shower).
Install toilet drain and flange
3 inch PVC pipe to toilet location.
Drain elbows up through subfloor at marked location.
Toilet flange installs flush with finished floor (or 1/4 inch above).
Flange anchored to subfloor with screws.
Install tub/shower drain
2 inch PVC drain to tub or shower location.
Trap (P-trap) below floor level.
Specific drain location per tub/shower spec sheet.
Install sink drain
1.5 inch drain in wall behind sink location.
Stub out at 18 inches above floor.
P-trap connection occurs at sink install (after rough-in).
Run vent pipes
Each fixture vented within code distance of trap.
Vents rise vertically through framing.
Connect to main vent stack (existing) or run new vent through roof.
PVC pipe, primer, and cement.
Run hot and cold water supply
PEX or copper from main water supply.
Hot water (insulated to retain heat).
Cold water.
To each fixture's location.
Stub out: typically 22-24 inches above floor for sink, in valve body for tub/shower.
Install tub/shower mixing valve rough-in
Mixing valve body installed in wall.
Hot and cold supply connect to valve inlets.
Outlets: shower head and tub spout pipe stub outs.
Per valve manufacturer's installation depth from finished wall surface.
Pressure test before drywall
Cap all open ends.
Pressurize supply lines to 100+ PSI; verify no drops.
Add water to drain system; verify no leaks at joints.
Hold pressure for 30+ minutes.
Schedule rough-in inspection
Inspector verifies pipe sizes, slope, connections, vent placement.
Pass: continue with insulation and drywall.
Fail: fix and re-inspect.
Common mistakes that cost you
- Wrong fixture rough-in dimensions. Fixture doesn't fit. Always verify spec before roughing.
- Insufficient slope. Drains don't drain. 1/4 inch per foot mandatory.
- Missing or wrong venting. Traps siphon dry; sewer gas. Code-specified vent placement.
- Unpressed PEX or untested joints. Hidden leaks behind drywall. Always pressure-test.
- DIY without permit. Code violations, insurance issues. Always permit.
Frequently asked questions
Can I do bathroom plumbing rough-in myself?
With Ontario homeowner plumbing permit: yes for own residence.
Most homeowners hire licensed plumber.
Cost drivers: number of fixtures, drain and vent routing, whether you're moving existing lines, slab vs. joist access, and finish-floor conditions.
DIY mainly saves on labour, but you still carry materials, the homeowner plumbing permit, and inspection — and any rework if it fails.
What's the typical rough-in for a toilet?
Drain: 12 inches from finished wall to drain centre (most common).
Some toilets: 10 inch or 14 inch — verify before purchase.
Supply: 7 inches above floor, 6 inches to one side of drain.
How do I connect to existing plumbing?
Existing copper supply: cut, install transition fitting, run new PEX from there.
Existing main drain: cut and install T-fitting at branch point.
Older galvanized supply: best to replace entirely (galvanized degrades).
When to call us instead
Bathroom rough-in plumbing is part of every basement and bathroom renovation. Our licensed plumbers handle it as part of the scope.
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