How much does it cost to replace the floor under a toilet?

Quick Answer

Replacing the floor under a toilet typically costs $200 to $600. The average cost is around $400. The exact price depends on factors like the size of the area being replaced, the materials used, and if plumbing modifications are needed. In most cases, the toilet must be removed to access and replace subflooring. This involves disconnecting and capping water lines. Rotted or damaged subfloor panels are cut out and replaced with new plywood or OSB. Floor leveling compound or self-leveling underlayment may be required to create a smooth, even surface for the new flooring. Labor accounts for 50-70% of the total project cost.

What’s Involved in Replacing Subflooring Under a Toilet

Replacing the subfloor under a toilet is moderately complex. Here are the basic steps involved:

  • Turn off water supply and flush toilet to empty tank
  • Disconnect and remove toilet
  • Cap water supply lines
  • Cut out damaged subfloor with saw or utility knife
  • Install new plywood/OSB subfloor panels
  • Use leveling compound if needed to create flat surface
  • Reinstall toilet on new subfloor
  • Reconnect water supply lines
  • Turn water back on and test for leaks
  • Caulk around base of toilet

The existing flooring around the toilet is not usually affected. However, if vinyl, laminate, or wood flooring runs under the toilet, it may need to be removed and reinstalled after the subfloor replacement.

Subfloor Materials

Plywood and oriented strand board (OSB) are the most common subfloor materials used under toilets:

  • Plywood – Moisture-resistant plywood like CDX is ideal for bathrooms. Thickness is typically 3⁄4″. Avoid particleboard as it can swell and delaminate when exposed to moisture.
  • OSB – OSB is a sturdy, affordable subfloor choice. Look for panels rated Exposure 1 for wet areas.

The subfloor should be thick enough to feel solid when walked on, without flexing or squeaking. Consult local building codes for minimum thickness guidelines. Match the existing subfloor thickness if possible.

Cost Factors

Several factors affect the cost to replace subflooring under a toilet:

  • Size of the repair – A larger area of damaged subfloor will require more materials and labor to replace.
  • Subfloor material – OSB is cheaper than plywood.
  • Toilet modifications – Adjusting supply lines, valves, flanges or drains adds cost.
  • Access issues – Subfloors are harder to replace in tight spaces.
  • Floor leveling – Leveling products add $10-$25 per bag.
  • Flooring removal/replacement – Taking up surrounding flooring increases labor time.
  • Plumbing modifications – Moving pipes, drains or vents is time consuming.

Get multiple estimates to find the best price if replacing a large section of subfloor under a toilet.

DIY vs Hiring a Professional

Homeowners comfortable using tools can DIY subfloor replacement under a toilet:

Pros of DIY:

  • Save on labor costs
  • Greater schedule flexibility
  • Sense of accomplishment

Cons of DIY:

  • Inexperience can lead to mistakes
  • Project takes more time
  • Physical demanding work
  • Proper disposal of old materials

Hiring a professional ensures the job is done right but costs more in labor:

Pros of hiring a pro:

  • Experienced with plumbing disconnection
  • Proper tools to cut out subfloor
  • Knowledge of building codes
  • Smoother finished surface
  • Warranty on work

Cons of hiring a pro:

  • More expensive, $200-$400 for labor
  • Wait time for contractor scheduling
  • Variable service quality

Cost to Replace Subfloor Under Toilet by Location

Subfloor replacement costs vary across the country based on labor rates:

City Cost Range
Seattle, WA $350 – $550
Atlanta, GA $300 – $450
Houston, TX $250 – $400
Philadelphia, PA $400 – $600
Chicago, IL $350 – $500
Phoenix, AZ $250 – $400
San Antonio, TX $250 – $400
San Diego, CA $400 – $600
Dallas, TX $300 – $450
San Jose, CA $350 – $550
Jacksonville, FL $300 – $450
Indianapolis, IN $300 – $450
Austin, TX $300 – $500
Columbus, OH $350 – $500

Get free estimates from local contractors to determine exact costs in your area. Expect to pay more for emergency repairs or rush jobs.

Toilet Subfloor Damage Causes

Several issues can damage the subfloor under a toilet:

  • Leaks – Leaks from the toilet, supply line, drain pipe or wax ring slowly rots the subfloor.
  • Installation issues – Improper toilet installation can crack or warp subfloor panels.
  • Moisture – Urine, spills, condensation or excess humidity rots the subfloor over time.
  • Weight – Heavy loads cause the subfloor to depress or fracture.
  • Dry rot – Bacteria and fungi feed on the subfloor causing decay.
  • Pests – Termites, carpenter ants or rodents can damage the subfloor.

Prevent subfloor damage by fixing any leaks immediately. Also caulk around toilets and use bathroom exhaust fans to minimize moisture issues.

Toilet Subfloor Preparation

Proper preparation is key to a successful subfloor installation under a toilet:

  • Remove old fasteners, adhesive or vapor barriers from the subfloor.
  • Scrape off wax ring residue using a putty knife.
  • Cut substrate panels slightly larger than the space to allow trimming.
  • Dry fit subfloor pieces to ensure proper fit.
  • Follow manufacturer’s installation guidelines for spacing and fastening.
  • Prime subfloor panels before applying leveling products if needed.

Taking time to prep helps prevent squeaks, damage to flooring or leaks when reinstalling the toilet.

Cost to Repair Rotted Subfloor vs. Complete Replacement

For minor damage under one section of a toilet, subfloor repair by cutting out and replacing only the rotted area costs $150-$300. This saves money compared to replacing the entire bathroom subfloor.

However, if there is extensive damage or the leak source is unidentified, a full subfloor replacement may be needed. This costs an average of $1,200-$1,800 for a 5×7 bathroom.

The choice depends on:

  • Extent of damaged area – Smaller patches are cheaper to replace
  • Access to damaged subfloor – Repair is harder in tight spaces
  • Match to existing subfloor – Replacing the whole subfloor ensures an even surface
  • Ability to find and fix leak – Repair is temporary if leak persists

Getting professional advice is recommended to determine the best option.

Alternative to Replacing Toilet Subfloor

For minor subfloor damage, an alternative to replacement is using an epoxy patch kit:

  • Kits contain two-part epoxy compound to fill holes or dents
  • Levels out damaged area for smooth toilet installation
  • Much quicker than cutting out and replacing subfloor
  • Costs only $25-$50 per kit
  • Not recommended for large areas greater than 16” x 16”

DIYers can easily apply epoxy patch products. It works as a temporary repair but does not address extensive rot or structural issues.

Toilet Subfloor Code Requirements

The International Residential Code (IRC) outlines minimum standards for toilet subfloors:

  • Subfloor must be smooth, rigid and free of decay
  • No more than 1⁄4” variation in surface flatness over 32”
  • Framing spacing under subfloor not to exceed 16” o.c.
  • Minimum subfloor thickness over joists: 3⁄4” plywood or 23/32” OSB
  • Fasten panels at 6” o.c. around perimeter, 12” o.c. with screws or 8d nails
  • 1⁄8” spacing allowed between panels
  • Seams offset from framing members by at least 4”

Consult local building codes for any additional subfloor requirements or restrictions in your area. Failing to follow code can void permits or cause plumbing leaks.

Conclusion

Replacing the subfloor under a toilet generally costs $200 to $600 depending on the repair size, materials, and if flooring removal or plumbing modifications are required. DIY is possible but involves disconnecting the toilet and cutting precise openings. Hiring a pro ensures proper building code compliance and finishes the job quicker with fewer mistakes. Prevent subfloor damage by fixing toilet leaks immediately before extensive repairs become necessary.