Bathroom & Kitchen Renovation Plumbing: What to Plan Before You Demo

Every year I get calls from homeowners mid-renovation who've just discovered something unexpected behind the walls — galvanized pipes that need replacing, drains that don't line up with the new layout, or a hot water tank that can't keep up with the new soaker tub they just bought. These surprises are avoidable if you plan the plumbing before you start the demo.

Whether you're renovating a bathroom, gutting a kitchen, or doing both at once, the plumbing work is usually the most critical part of the project. It determines your layout, drives your timeline, and can make or break your budget. Let me walk you through what to think about before you pick up a sledgehammer.

Before You Demo: The Plumbing Assessment

Before any demolition begins, you need a plumbing assessment. This isn't just about what you want the finished room to look like — it's about understanding what's behind your existing walls and under your floors.

What a Pre-Renovation Assessment Covers

• Existing pipe condition: What materials are your current supply and drain lines? Copper, galvanized, PEX, ABS, cast iron? Older homes may have galvanized steel pipes that are corroded and should be replaced while the walls are open.
• Drain locations: Where are the existing drain lines and vent stacks? Moving a toilet drain, for example, requires access to the subfloor and can be one of the most expensive plumbing changes.
• Water supply capacity: Can your existing supply lines handle additional fixtures? Adding a double vanity or a body spray shower system may require upsized supply lines.
• Hot water capacity: Your current water heater may not support a large soaker tub or rain shower. This is a good time to evaluate whether you need a hot water tank replacement.
• Shut-off valves: Older homes often lack individual shut-off valves at each fixture. The renovation is the perfect time to add them.

Bathroom Renovation Plumbing

Layout Changes

The biggest cost driver in bathroom renovation plumbing is moving fixtures. Keeping fixtures in the same locations (or close to them) is the most cost-effective approach. Here's how fixture moves affect your budget:

• Toilet: Moving a toilet is one of the most expensive changes because it requires relocating the 3" or 4" drain line. If you can keep the toilet in the same location, do it.
• Shower/tub: Moving a shower or tub involves relocating both supply lines and the drain. The drain is the bigger challenge, especially if the shower is on a concrete slab.
• Vanity/sink: Vanities are the easiest fixture to relocate because the supply and drain lines are smaller and more flexible.

Common Bathroom Plumbing Upgrades

• Replacing old shut-off valves with quarter-turn ball valves
• Upgrading to a thermostatic shower valve (consistent temperature even when someone flushes a toilet)
• Adding a second sink to the vanity
• Installing a heated towel rack (requires a dedicated water line for hydronic models)
• Upgrading the toilet to a low-flow or dual-flush model
• Adding floor drain requirements for walk-in showers

Kitchen Renovation Plumbing

Sink and Dishwasher Considerations

The kitchen sink is the hub of kitchen plumbing. When you move or upgrade the sink, everything connected to it is affected:

• Drain connection: The sink drain connects to the main drain stack. Moving the sink across the kitchen means extending the drain line, which must maintain proper slope.
• Dishwasher: The dishwasher connects to the sink's drain and hot water supply. Its placement is limited by the distance to these connections.
• Garbage disposal: If you're adding a disposal, the drain setup changes and you may need a dedicated electrical circuit as well.
• Pot filler: A wall-mounted pot filler over the stove requires a cold water line run to that location during the renovation.

Gas Line Changes

If you're switching from an electric to a gas range, or adding a gas line for a new range location, this requires a licensed gas fitter. Gas line work must be permitted, inspected, and pressure-tested before it can be used.

What to Do When Walls Open Up

Once demolition starts and you can see inside the walls, take advantage of the opportunity. This is the time to address problems that would be expensive to fix later:

• Replace galvanized pipes: If you find old galvanized steel water lines, replace them with PEX or copper. Galvanized pipes corrode from the inside, restrict flow, and will eventually leak.
• Add shut-off valves: Install quarter-turn ball valves at every fixture for easy maintenance in the future.
• Upgrade vent lines: Proper venting prevents slow drains and gurgling. If your existing venting is inadequate, now's the time to fix it.
• Insulate pipes: Any supply lines running through exterior walls should be insulated to prevent freezing.
• Address water quality: If you're on well water, a renovation is a good opportunity to plan for water treatment. Your plumber can pre-plumb for a softener or filtration system.

Timing Your Plumbing Within the Renovation

Plumbing work typically happens in two phases during a renovation:

Phase 1: Rough-In (After Demo, Before Drywall)

• Relocate or install new supply lines
• Move or extend drain and vent pipes
• Install shower valve bodies and tub drains
• Run any new gas lines
• This phase must be inspected before walls are closed

Phase 2: Fixture Installation (After Finishing)

• Install sinks, faucets, and vanities
• Set toilets
• Install shower heads, trim kits, and accessories
• Connect dishwasher and other appliances
• Final testing and adjustments

The gap between these two phases is when the other trades do their work — drywall, tiling, painting, and flooring. Poor scheduling is one of the biggest reasons renovations run over budget. Make sure your contractor and plumber coordinate timing closely.

Renovation vs. New Construction Plumbing

Renovation plumbing is generally more complex and more expensive per fixture than new construction plumbing. In new construction, you're working with open framing and clean access. In a renovation, you're working around existing structures, dealing with surprises in the walls, and trying to connect new work to old systems. The CMHC's renovation planning resources can help you budget and plan for these complexities. This is why having an experienced plumbing services team matters.

Choosing Fixtures: Practical Considerations

When selecting fixtures for your renovation, keep these practical plumbing considerations in mind:

• Water pressure requirements: Some rain shower heads and body spray systems require higher water pressure than older homes can provide.
• Drain compatibility: Not all tubs and sinks fit every drain configuration. Confirm compatibility before purchasing.
• Mounting requirements: Wall-mounted faucets and toilets need specific blocking and framing installed during the rough-in phase.
• Water efficiency: Low-flow fixtures save water and reduce the load on your hot water tank and septic system. Look for products with the ENERGY STAR Canada or WaterSense certification for the best water and energy savings.

Frequently Asked Questions

How much does renovation plumbing cost?

Renovation plumbing costs vary widely depending on the scope of work. Replacing fixtures in their existing locations is the most affordable option. Moving fixtures, adding new ones, or replacing old piping costs more. The best way to get an accurate estimate is to have a plumber assess your project before demolition begins — this avoids the costly surprises that drive budgets up.

Can I move my toilet to a different wall during a bathroom renovation?

Yes, but it's one of the more expensive plumbing changes. The toilet connects to a 3" or 4" drain line that runs through the floor or subfloor. Moving it requires rerouting this drain while maintaining proper slope. If your bathroom is on a concrete slab, the concrete may need to be cut and repaired, adding significant cost.

Should I replace old pipes during a renovation?

If your walls are already open and you have old galvanized steel pipes, absolutely replace them. Galvanized pipes corrode from the inside, restricting water flow and eventually leaking. Replacing them with PEX or copper while the walls are accessible costs a fraction of what it would cost to do as a separate project later.

Do I need a permit for renovation plumbing in Manitoba?

Yes. Most plumbing changes beyond simple fixture swaps require a permit in Manitoba. This includes moving fixtures, adding new fixtures, replacing supply or drain lines, and any gas line modifications. Your plumber should handle the permit process and schedule required inspections. Unpermitted work can create issues when selling your home.