Subfloor Repair Cost Calculator

This is the single biggest driver of cost. A small soft spot under 20 sq ft might be a half-day patch job at $150-$300 in labor. A bathroom where the subfloor has been wet for months can require replacing 100+ sq ft, sistering multiple joists, and treating for mold - a job that runs $1,500-$4,500. Before budgeting, probe the perimeter of any soft area with a screwdriver; rot often extends 12-18 inches beyond where you feel the give.

OSB (oriented strand board) is the cheaper repair material at $25-$35 per sheet for 3/4-inch tongue-and-groove panels, but it swells if exposed to moisture again. 3/4-inch plywood costs $45-$65 per sheet and handles humidity better - most contractors use it for bathrooms and kitchens even if the original subfloor was OSB. Cement board ($15-$25 per sheet) is required under tile in wet areas and adds material cost but prevents future water damage from causing rot.

Joist sistering - attaching a new full-length joist alongside a damaged one - adds $200-$600 per joist depending on length and access. If joists are structurally compromised (hollow from rot or insect damage), they may need full replacement rather than sistering, which can require temporary support beams and runs $500-$1,500 per joist. A crawl space inspection or floor probe before committing to a repair budget is essential.

Subfloor access from above is standard but requires removing the floor covering first. Crawl space access from below adds labor time - tight crawl spaces under 18 inches of clearance can double the labor rate as contractors work in cramped conditions. Finished ceilings below the subfloor (like a first-floor bathroom over a finished basement) add cost for ceiling repair after sistering. Expect $100-$300 extra for tight crawl space work; $400-$800 if finished ceiling below needs patching.

The subfloor is always under something - carpet, vinyl, tile, hardwood, or laminate. Carpet removal is cheap ($0.50-$1.50 per sq ft). Tile removal is expensive and slow at $2-$5 per sq ft. Hardwood removal that preserves the boards for reinstallation costs $3-$6 per sq ft in labor. If the floor covering is being replaced anyway (common when subfloor damage is extensive), the removal cost is absorbed into the flooring project - but budget for it separately if you're patching and reinstalling.