How much does it cost to replace all the supply and drain lines during a bathroom gut reno in the GTA?

Replacing all supply and drain lines during a bathroom gut renovation in the GTA typically costs $3,500–$8,000 for plumbing alone, depending on the scope, pipe material, accessibility, and whether you're working in a house or a condo.

When you strip a bathroom down to the studs, it's the ideal time to replace aging plumbing — and in many older Toronto homes, it's not optional. If your home was built before 1970, there's a good chance you're looking at galvanized steel supply lines that are corroded and restricting water flow, and cast iron drain stacks that may be deteriorating from the inside out. Homes in established neighbourhoods like the Danforth, High Park, Leaside, and the Beaches commonly have this original plumbing, and a gut renovation is your one chance to replace it without tearing apart finished walls later.

Supply Line Replacement

Replacing copper or galvanized supply lines with new copper or PEX typically runs $1,500–$3,500 for a standard bathroom. PEX (cross-linked polyethylene) has become the dominant choice in GTA bathroom renovations because it's faster to install, resistant to freeze damage — a real consideration given Toronto's winters where temperatures regularly hit -15 to -20°C — and costs less in both material and labour. Copper remains a solid choice and is preferred by some Toronto plumbers, but it costs roughly 30–40% more in materials and takes longer to install due to soldering.

A typical bathroom supply line replacement includes new hot and cold lines from the main stack or manifold to the shower valve, vanity faucet, and toilet. If your existing shut-off valves are gate-style (the round handle type common in older GTA homes), your plumber will replace them with quarter-turn ball valves at each fixture — a small upgrade that makes a huge difference in an emergency.

Drain Line Replacement

Drain and waste line replacement runs $2,000–$5,000 depending on complexity. This includes the toilet drain (typically 3-inch or 4-inch ABS), shower or tub drain (2-inch), vanity drain (1.5-inch), and all connecting vent piping. If the existing cast iron stack needs to be replaced with ABS within the bathroom, expect to be at the higher end of that range.

The Ontario Building Code requires specific drain pipe sizes, slopes (minimum 1/4 inch per foot for horizontal runs), and venting configurations. Every fixture needs a properly sized trap and must be connected to the vent system to prevent sewer gas from entering your home. Your licensed plumber will ensure all rough-in work meets code before the City of Toronto plumbing inspector arrives.

What Affects the Final Cost

Several factors push costs higher in the GTA market. Accessibility is the biggest variable — if drains run through a concrete basement floor, cutting and patching concrete adds $500–$1,500. Condo renovations are more complex because you're working with shared plumbing stacks that cannot be modified, and any work near the stack requires careful coordination. Permit fees for plumbing work in Toronto typically run $150–$400, and inspection scheduling can add a day or two to your project timeline.

A licensed GTA plumber will typically quote this work as a flat rate rather than hourly ($85–$150/hour), which protects you from cost overruns. Always confirm that the quote includes permits, inspection coordination, and all materials.

The Bottom Line

If you're already doing a gut renovation, replacing supply and drain lines adds roughly 15–25% to your total project cost but eliminates the risk of plumbing failure for the next 40–50 years. Trying to save money by leaving old galvanized or deteriorating cast iron behind new tile is one of the most common regrets GTA homeowners report after a bathroom renovation. Get matched with a bathroom contractor for a free estimate on your project through Toronto Bath Remodeling.