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How Are Sagging Floors Fixed?

Thursday, April 15th, 2021
sagging floors

Sagging floors are usually a visible sign of deteriorated structure somewhere below. In many cases, the factor causing this deterioration is water damage originating from above—such as severe indoor flooding— inside the crawl space. Chronic moisture in basements may also affect floor structure. Two components of the floor may be affected by sagging:


These are the wide wooden panels that lie directly below your flooring. Typically standard plywood or OSB (oriented strand board) subfloors can be affected by water damage inside the house due to flooding, ruptured pipes, or other causes. If water is present long enough to seep through flooring and saturate the subfloor, sagging may occur in spans of subfloor between the supporting joists beneath.  


Joists are wood beams, evenly spaced and running parallel to each other beneath your floor structure. Joists are vulnerable to water damage due to flooding in the crawl space from outdoor sources such as heavy rain or from chronic leaks in plumbing pipes routed through the basement. Water-related deterioration causes joists to weaken, resulting in sagging floors above.

Fixing Sagging Floors

In many cases, water-damaged subfloors must be entirely removed and replaced with new wood. However, if a wet subfloor is quickly opened up—flooring, tile, or other material removed—before it has absorbed too much water, and the material subjected to continuous drying processes by qualified water damage professionals, the wood may be effectively saved and sagging prevented. Once subfloor panels are fully saturated for any length of time, however, replacement of the affected wood is often necessary to prevent sagging floors and other deformation.  

Two methods may be applied to deteriorated floor joists that cause sagging floors. “Sistering” is a procedure where a sagging joist is jacked up to level, then a new, fully intact joist board is attached to the existing joist to straighten it and restore structural stability. Where the original board is not severely deteriorated, this eliminates the need to remove existing joists. Alternatively, multiple jacks may be utilized to level sagging floors, then each existing joist is removed and replaced with a new board.