Sagging Floors Over a Crawl Space: Causes and Fixes

Floors that bounce, slope toward the middle of the house or crack drywall above usually point to the framing under them. In homes on crawl spaces, common causes are posts set on poor footings, beams too small for their span, and wood weakened by moisture.

Added posts. Angi puts the average for a support post at about $2,500 (2026). Sistered joists run $150 to $325 each (HomeGuide). A new beam with posts is $1,000 to $5,000 (HomeGuide).

Moisture comes first. If moisture weakened the wood, a vapor barrier or encapsulation keeps the repair dry. See crawl space repair.