How much does it typically cost to replace a rotten shower subfloor and re-waterproof everything in a Richmond Hill bathroom?

Replacing a rotten shower subfloor and re-waterproofing in Richmond Hill typically costs $3,500–$8,500 for the subfloor and waterproofing work alone, with total project costs reaching $12,000–$25,000 once you account for new tile, fixtures, and finishing trades.

The wide range reflects how far the water damage has spread. A localized soft spot directly under the shower base is a very different scope than rot that has wicked into the surrounding bathroom floor, travelled into wall framing, or compromised the floor joists below. Until a contractor opens the floor, nobody can give you a firm number — and any quote you receive before demolition should be structured with a clear allowance for additional rot discovered during the work.

What Drives the Cost in Richmond Hill

Richmond Hill's housing stock is heavily weighted toward 1980s–2000s suburban homes — two-storey and backsplit layouts with second-floor master ensuites or main bathrooms sitting above finished basements or living spaces. When the shower subfloor in one of these bathrooms fails, water has often been travelling silently for years before the soft spot becomes noticeable underfoot. By the time you feel the floor flex, the OSB or plywood subfloor is typically saturated, the floor joists may have surface mould or early rot, and the bottom plates of the surrounding stud walls may be compromised as well.

The subfloor replacement itself — cutting out the damaged section, sistering or reinforcing any affected joists, and installing new 3/4-inch tongue-and-groove plywood or OSB — runs $1,500–$3,500 depending on the extent of damage and how much structural reinforcement is needed. If joists need sistering or partial replacement, add $500–$1,500 for that carpentry work. A licensed contractor should also inspect the ceiling below for water staining, which signals that moisture has been dripping through — that ceiling may need repair as well.

Re-waterproofing is where you absolutely cannot cut corners. The correct approach for a shower rebuild in 2025 is a full sheet membrane system like Schluter Kerdi or a liquid-applied membrane like Laticrete Hydro Ban or Mapei AquaDefense applied over cement board or a foam shower tray. The membrane must cover the entire shower floor, all walls up to at least 6 inches above the showerhead rough-in, and integrate properly with the drain assembly. A properly installed waterproofing system costs $800–$2,000 in materials and labour for a standard 3x4 or 3x5 shower — and it is the single component that determines whether your new shower lasts 20 years or fails again in five.

The Full Scope Reality

Most Richmond Hill homeowners doing this repair end up with a near-complete shower rebuild, because once the tile comes off and the subfloor is replaced, you are essentially starting fresh. Budget for: demolition and disposal ($500–$1,200), subfloor replacement ($1,500–$3,500), structural repairs if needed ($500–$1,500), cement board and waterproofing ($800–$2,000), new porcelain tile for the shower ($2,500–$5,000 installed for a standard shower), new shower drain ($200–$500), and new shower valve and trim if the existing one is being replaced ($600–$1,500 installed by a licensed plumber). A new glass door or enclosure adds another $1,200–$3,500.

You will also need a plumbing permit from the City of Richmond Hill (York Region) if the drain is being modified or relocated, and an ESA electrical inspection if any electrical work is involved (heated floor, exhaust fan, etc.).

Practical Tips

Get the contractor to photograph and document all rot and damage before closing the walls — this protects you and gives you a clear record of what was found and repaired. Ask specifically how they plan to handle the drain-to-membrane transition, because this joint is where most shower waterproofing failures originate. A Schluter Kerdi-Drain or equivalent bonding flange that integrates directly with the membrane is the right answer.

Do not let anyone talk you into applying RedGard or a liquid membrane directly over drywall in the shower — cement board or a foam substrate is the correct base. And if mould is found in the wall cavity during demolition, that needs professional remediation before the shower is rebuilt, not just a bleach wipe-down.

Toronto Bath Remodeling can match you with experienced Richmond Hill bathroom contractors who handle exactly this type of water damage rebuild. Browse local professionals through the Toronto Construction Network directory at torontoconstructionnetwork.com/directory?category=bathroom-renovations or get matched for a free estimate on your project.