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 with modest labor. A bathroom where the subfloor has been wet for months can require replacing 100+ sq ft, sistering multiple joists, and treating for mold, which pushes the job toward the top of the range. 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 for 3/4-inch tongue-and-groove panels, but it swells if exposed to moisture again. 3/4-inch plywood costs more per sheet and handles humidity better - most contractors use it for bathrooms and kitchens even if the original subfloor was OSB. Cement board 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 - is typically priced per joist (HomeAdvisor puts sistering at $100-$300 per joist and Fixr puts joist replacement at $125-$315), 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. 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 slow the work and raise labor costs 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 extra cost for tight crawl space work, and more again if a finished ceiling below needs patching.

The subfloor is always under something - carpet, vinyl, tile, hardwood, or laminate. Carpet removal is cheap. Tile removal is expensive and slow. Hardwood removal that preserves the boards for reinstallation costs more 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.