Three Signs It’s Time to Replace a Subfloor

replace a subfloor

If water damage occurs inside a house, is it always necessary to replace a subfloor?  Made of standard plywood, particleboard, or OSB (oriented strand board), the subfloor is attached directly to the top of house floor joists. Because it’s a critical structural component that supports the weight of everything inside a given room, knowing whether it’s time to replace a subfloor is important.

Once a subfloor is significantly soaked due to water damage, it will not properly dry on its own. Intervention by qualified water damage specialists is required to mitigate potential consequences. Here are three factors to assess the condition and determine whether to replace a subfloor.

Type of Wood

The specific wood composition may be decisive in the decision to replace a subfloor.

  • Particleboard is most susceptible to water damage. This material swells rapidly when wet and permanently loses structural integrity. Following water damage, it’s often simpler and more cost-effective to replace a subfloor made of particleboard than try to salvage it.  
  • OSB (oriented strand board) is another composite subfloor type, but somewhat more resistant to water than particle board if the drying process is initiated in time.
  • Plywood is usually the most water-resistant subfloor and may be salvageable if the professional response includes water extraction, air drying, and dehumidification, as well as industry-standard decontamination methods.

Source of Water

If water damage is Category 1—“clean” water such as from a broken indoor water line—salvaging an OSB or plywood subfloor is most likely if treated rapidly.  

Category 2 “gray” water from overflowing fixtures and other unsanitary sources may contain microorganisms. Professional disinfection techniques must be applied to retain the floor.

If saturated by Category 3 “black” water—raw sewage or outdoor flooding— decontamination is not feasible and it will be necessary to replace a subfloor.

Timely Response

Generally, the maximum window of opportunity for salvaging a wet subfloor is 72 hours following water damage. After that time frame expires, toxic mold growth becomes an issue and it may be preferable to replace a subfloor in order to decisively eliminate this potential source of indoor contamination.

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