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Most of the work happens at the rough-in stage, once the framing is up and before the walls are closed. The plumber brings water to each fixture location, runs drains at a steady slope to the stack or building drain, and adds the venting that lets them flow. After the new piping is tested and inspected, the walls are finished, and the plumber returns to set the fixtures once tile, cabinets and counters are in.
Because it changes the plumbing system itself, this is the work that plumbing codes, permits and licensing rules are written for. Careful planning at the start, from the exact position of each fixture to where the shut-off valves will sit, costs little and spares you from opening finished walls later.
Plumbing installation projects: bathroom rough-ins, kitchen moves, basement suites and additions
- New bathroom or powder room: hot and cold supplies plus a vented drain for the toilet, the sink and the tub or shower, often in a space that never had plumbing.
- Kitchen relocation or island sink: moving the sink means new drain and vent routes, and an island is harder to vent because there is no wall above it.
- Basement bathroom or suite: when fixtures sit lower than the sewer connection, a pumped system lifts the wastewater, and drains are usually cut into the slab.
- Laundry room or wet bar: a standpipe or laundry sink drain, supply valves you can reach, and a floor drain where the layout allows.
- Addition: new supply and drain branches extended from the existing system, which has to be able to carry the extra fixtures.
- Repiping during a renovation: replacing aging supply lines while the walls and ceilings are already open.
Rough-in plumbing explained: supply lines, drains, vents and the finish stage
Rough-in is everything behind the walls and under the floor. Supply lines branch from the main to each fixture and end in capped stubs or valves at the height and spacing the chosen fixture needs. Drains must fall continuously toward the stack, each fixture gets a trap that holds water to block sewer gas, and vents let air into the system so water drains smoothly and the traps aren't siphoned dry. A toilet flange, shower drain or vanity outlet placed a little off is easy to move now and costly to move once the tile is down, which is why fixtures are usually chosen before rough-in starts.
Before anything is covered, the new piping is tested for leaks and, where a permit applies, inspected. Insulation, drywall, waterproofing and tile follow. The finish stage comes last: the plumber sets the toilet, connects the vanity and sink, installs the trim on the shower or tub valve, and runs each fixture to check the flow and look for leaks at every connection.
PEX or copper for new supply lines, and how the piping is laid out
Most new supply piping in Canadian houses is either PEX or copper, and a plumber will choose based on the existing system, access through the framing, the layout and local practice. Both give good service when they are installed to the manufacturer's instructions and the local code; the differences are practical rather than a question of one being safe and the other not.
- PEX: flexible tubing that bends around framing in long runs with few joints; its fittings and crimp or expansion tools must belong to the same system, and it has to be kept out of sunlight.
- Copper: rigid and long proven, neat on exposed runs and near the water heater, joined by soldering or mechanical fittings, with care taken around wood framing when soldering.
- Home-run manifold: a separate line from a central manifold to each fixture, often with a valve for each, so one fixture can be shut off without affecting the rest.
- Trunk and branch: a main line with tees to each fixture, the traditional layout with copper, which uses less pipe and fewer long runs.
- Drains and vents: new work usually uses plastic drain pipe, sized for the fixtures it serves and supported so it keeps its slope.
Shut-off valves in new plumbing: planning where the water can be turned off
A renovation is the cheapest moment to make the plumbing easy to control. When each fixture and each new branch has its own reachable valve, a future leak or repair means closing one handle instead of draining the whole house. Quarter-turn valves are easier to close fully than old multi-turn stops, and a label on each branch valve tells the next person what it serves.
- Put individual stops under every sink and behind every toilet, reachable without removing a drawer or panel.
- Plan an access panel or removable trim for tub and shower valves so the cartridge and stops can be serviced later.
- Give a basement suite, an addition or a new bathroom its own labelled branch valve.
- Add isolation valves for the water heater, the dishwasher, the fridge water line and the washing machine.
- Have the main shut-off checked before work starts, since the plumber will rely on it and an old valve that won't close is best replaced now.
Backflow and cross-connections: protecting drinking water in new plumbing
The City of Toronto describes backflow as the undesired reversal of water flow against its normal direction. At home it can happen wherever the drinking water supply is linked to something that could push or siphon dirty water back into the pipes: a hose left in a laundry tub or a pail of cleaner, a lawn irrigation system, a hydronic heating boiler, or the drain line of a water treatment unit. Such a link is known as a cross-connection.
Good new plumbing avoids these links by design, with an air gap where a supply or appliance drain discharges, vacuum breakers on hose connections, and a suitable backflow preventer where an irrigation or heating system ties into the supply. Toronto's backflow prevention program targets industrial, commercial and institutional properties, larger residential buildings and construction sites rather than houses, but the same risk exists at home, so ask your plumber how each new connection is protected.
Plumbing permits, inspections and licensed plumbers for new installations
Adding fixtures, running new drains or rerouting piping changes the plumbing system, and municipalities generally expect a permit and inspections for it. The City of Toronto, for example, issues a stand-alone plumbing permit for plumbing work that isn't related to other construction on the building, and its fee schedule lists fixtures, piping, water services and drains among the items covered. When the plumbing is part of a bigger renovation, ask whether it falls under the project's permit or needs its own, and book the rough-in inspection before any wall is closed.
Hire a plumber qualified for new work in your province. In Quebec, that means a contractor with the appropriate Régie du bâtiment du Québec licence, which plumbing contractors obtain through the CMMTQ; the narrow exception for owners of a single-family home they live in doesn't lift the obligation to meet the code. Elsewhere, ask for the licence or trade certificate your province requires, and leave any gas piping to a qualified gas technician.
Plumbing and the other trades: sequencing a renovation rough-in
New plumbing shares the walls and floors with every other trade, and most rough-in headaches come from the order of the work rather than the pipes themselves. A short meeting on site before rough-in, with the layout marked on the floor, settles who goes where.
- Framing comes first, and a wall may need to be thicker to hold a drain and vent; cutting or drilling joists and studs beyond what the framing allows is a question for the designer or an engineer, not something to improvise.
- Drains and ducts compete for the same joist spaces, so the plumber and the heating contractor lay out their routes together.
- The electrician wires exhaust fans, heated floors, jetted tubs and any pump once the plumbing routes are set.
- Pipes in exterior walls or unheated spaces are insulated or rerouted before drywall goes up.
- Waterproofing and tile follow the plumbing inspection, and the tiler needs the final drain and valve positions.
- Cabinets and counters are installed before the finish plumbing, so sinks and faucets can be set and connected.
Plumbing Installation: frequently asked questions
What does rough-in plumbing include?
It includes the hidden part of the job: supply lines to each fixture location, drains with their traps, vents, and the connections to the existing stack and main. It ends with capped pipes at the right spots, a leak test and, where required, an inspection. Setting the toilet, sink and faucets is the finish stage, done after the walls are completed.
Do I need a permit to add a bathroom?
Usually, yes. A new bathroom adds fixtures, drains and vents, which is exactly the kind of change municipalities regulate. Check with your municipality's permit office before work starts; in Toronto, plumbing that isn't part of other construction has its own stand-alone plumbing permit.
Is PEX as good as copper for a renovation?
Both are accepted and both last when properly installed. PEX is quicker to run through open framing and has fewer joints; copper is rigid and neat on exposed runs. Your plumber's choice usually depends on the existing piping, the layout and where the pipe will be exposed to heat or sunlight.
Can I put a bathroom in a basement below the sewer line?
Yes, with a pumped system that lifts the wastewater up to the sewer connection. It needs its own vent, a sealed pit and an electrical connection by an electrician, and a permit is generally required. If the sewer is deep enough, the fixtures can drain by gravity through lines cut into the slab instead.
Can a kitchen sink be moved to an island?
Usually, but the drain has to run under the floor to the stack at a steady slope, and venting is the tricky part since there is no wall above the sink. The plumber will use a venting method your local code accepts, so plan it before the island and flooring are ordered.
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Written by the LokalMatch editorial team. Reviewed by Zubair Afzal on September 10, 2026. How we write and check our guides