Ontario's new building code came into force on January 1, 2025, and every permit issued since then runs under it. Most of the talk has been about framing and insulation. But your plumbing lives in that code too — Part 7 of the Ontario Building Code, aligned with the 2020 National Plumbing Code — and it's the part that decides whether your basement stays dry and your drains stay quiet.
Here's what it means when you touch the plumbing in your house.
1. Renovate the plumbing, and the current code comes with it
Swap a faucet or a toilet like for like and nothing changes. But move a fixture, add a bathroom, or finish a basement, and the new work gets inspected against the current code — not the code from when your house was built.
That's where surprise costs come from. The rough-in you planned might need a different vent run, a different drain route, or protection that wasn't there before. Better to know at the quote stage than at inspection.
2. Below-grade fixtures need sewer backup protection
Ontario's rule is simple: fixtures installed below grade, where they could be hit by a surcharge from the public sewer, need protection — a backwater valve. Subsoil drainage connected to the building sewer has to be protected the same way.
I install these for a living, and I can tell you the math. A backwater valve costs a few hundred dollars. A basement full of sewage costs tens of thousands and a fight with your insurance company. When you finish a basement or add a bathroom down there, this is not the line item to cut.
3. Vents and traps are what the inspector looks at hardest
Every fixture drains through a trap — the U-bend that holds water so sewer gas stays in the pipe where it belongs. For that trap to work, air has to get behind the water. That's the vent system, and it's the part nobody sees and everybody gets wrong.
Without proper venting, draining water siphons the trap dry, and then your bathroom smells like the sewer. Distances from fixture to vent, how vents tie together, where air admittance valves are allowed and where they aren't — this is all code, all checked, and all a lot cheaper to do right before the drywall goes up.
4. Basement suites need real plumbing, not just fixtures
The 2024 code made secondary suites more flexible, and I get asked about basement suites in Barrie constantly. What makes a suite legal on the plumbing side:
- Drainage and venting roughed in to code for every fixture, including a bathroom roughed in under the slab if you're planning ahead
- Shut-off valves so the suite's water can be isolated without shutting down the whole house
- Backwater protection for the below-grade fixtures
- A floor drain or pan where the laundry sits, so a leak doesn't become a flood
A suite roughed in wrong doesn't just fail inspection — it caps what your house is worth.
5. Radon gets in through your plumbing
The new code requires a radon rough-in in new homes, and here's the part nobody mentions: radon doesn't just come through cracks. It comes up through your sump pit and your floor drains — the plumbing openings in your slab.
A sealed sump lid and traps that stay wet (or have trap primers) are plumbing details that double as radon protection. If your basement ever gets tested and comes back high, these are the first places a mitigation crew looks.
6. On a septic system? Different rulebook
If your house isn't on a municipal sewer, your plumbing answers to Part 8 of the code — the septic rules — and this is where rural homeowners around Orillia and Muskoka get caught.
Your septic tank and leaching bed were sized for your house as it was built: the number of bedrooms and fixtures sets the design flow. Add a bathroom, a bedroom, or a basement suite, and you can push past what your system was designed for. The fix isn't optional — the system may need to be enlarged or replaced, and that work needs its own permit and inspection.
The code also sets minimum distances between your septic system and your well, your house, and your lot lines. So "we'll just put the new bed over there" isn't how it works. If you're planning an addition or a suite on a septic property, the septic check comes first — before the design, not after.
The bottom line
Plumbing code isn't bureaucracy. It's the difference between a basement that floods with sewage and one that doesn't, between drains that smell and drains that don't. When you get a quote for plumbing work in a renovated or finished space, ask whether it's priced to the current code — because that's what it will be inspected to.
Need plumbing work done right the first time? Free estimates, 24/7: https://conceptsplumbing.ca — or book a service call: https://calendly.com/conceptsinc/plumbing-estimate-service
Free Estimates. Honest Solutions.
— Mark Johnston, Concepts Plumbing, (705) 715-1513
