Water Damage to Subfloor Systems in Residential Buildings
Water damage to subfloor layers is easy to miss if you only watch the finish. Plywood or OSB under hardwood, tile, or carpet can stay wet after the face looks better. A wet subfloor is why a refinished hardwood fails, and why a new carpet should wait. This page is residential. Independent contractors measure and, when needed, open the assembly. We refer them. We do not invent a subfloor condition from a photo.
How water gets into a subfloor, and how you know
Supply leaks, appliance failures, wet crawlspaces, and wet slabs all reach this layer by different paths.
Meters should include the subfloor, not only the finish. Access from a basement or a crawlspace, if you have one, is often the honest way to see the underside. Soft spots, staining, swelling at joints, and a musty smell from a register or a closet are clues. OSB edges swell and can lose their fit. Plywood can often be dried if the water was clean and the time was short. Dirty water in a porous assembly is a removal discussion; see category 3 water damage.
The finished floor and the subfloor are a system. See water damage to hardwood floors, carpet water damage, and the hardwood cost page. A beautiful face with a wet underside is an incomplete job.
Drying versus replacement
Air at the edges is not always enough. Mats, openings, or removal may be required.
A contractor may use directed air, mats on a hardwood face, or removal of a section of finish to dry or to replace the panel. Replacement is more likely when the panel has swollen out of plane, when it is OSB that has failed at the edge, or when the water was unsanitary. Close the finish only after a documented dry standard. For crawlspace sources, see the broken-pipe-under-house page.
Frequently Asked Questions
Answers about drying a subfloor, OSB versus plywood, and when the finish has to come up.
Sometimes, if access from below exists or if mats and air can move moisture. Often a limited opening is needed. The contractor should say why.
Not as a slogan, but OSB tolerates wetting less well than good plywood. The decision follows the condition, not the brand name alone.
Because the hardwood can be the last thing to tell you. Cupping later, or odor, is how a skipped subfloor shows up.
A badly deteriorated subfloor can be. Stay off obviously soft floors and have them assessed. We refer water-damage contractors; a structural engineer is a different professional if the framing is in question.