The short answer
Signs of Rotting Subfloor
Walk barefoot across the room and press down with your weight. A rotting subfloor feels bouncy, soft, or spongy in certain spots, especially near toilets, sinks, or exterior walls. You might also notice the floor creaks more than usual, even in places that were quiet before.
Look for visual clues as well. Water stains, dark patches, or warped floorboards on the surface often mean moisture has reached the layer below. Gaps between baseboards and the floor, or a slight dip in the middle of a room, can signal that the subfloor has started to fail.
- Musty or earthy smell that persists
- Visible mold or mildew on floor seams
- Cracked or buckling floor tiles
- Doors that stick or no longer close properly
- Puddles or dampness that reappear after cleaning
Why Subfloor Rot Happens
Subfloor rot almost always comes from moisture that lingers too long. A slow leak in a pipe, an overflowing toilet, or a washing machine hose that drips behind the wall can soak the plywood or OSB under your flooring. Once wet, the wood starts to decay and loses its strength.
Humidity can also play a role. In warm, humid climates with rainy summers, moisture in the air may seep through cracks and keep the subfloor damp. Pay extra attention after heavy rain or storms, since water can find its way under floors more easily.
How to Test for Soft Spots
Use a small ball, like a tennis ball, and roll it across the floor. If it veers toward a particular area, that spot may have a slight depression from a sagging subfloor. You can also place a straightedge, such as a level, on the floor and check for gaps underneath.
Another simple test involves tapping the floor with the handle of a screwdriver. A solid subfloor sounds firm and dull, while a rotting one may sound hollow or give slightly under pressure. Be careful not to poke through the surface if the rot is advanced, as that could create a larger hole.
What to Do If You Suspect Rot
Stop using the affected area if the floor feels unstable. Move heavy furniture off the soft spots and avoid walking on them until the subfloor is checked. Turn off the water supply to any nearby fixtures if you suspect a leak, and wipe up standing moisture to prevent further soaking.
Contact local water damage pros for a thorough inspection. They can identify the source of moisture and assess how far the rot has spread. The sooner you act, the easier it is to contain the damage and avoid more extensive repairs to the floor joists or walls.
- Remove area rugs and wet padding right away
- Dry the surface with towels and a fan
- Check under sinks and around toilets for drips
- Keep the room ventilated to reduce humidity
Repair Options for Damaged Subfloor
Repairing a rotting subfloor usually involves cutting out the damaged section and replacing it with new plywood. The pros may also need to dry the area thoroughly and treat it for mold before installing the patch. This work often depends on how large the rotted area is and whether the floor joists are affected.
In some cases, the entire subfloor in a room may need replacement, especially if multiple soft spots exist or water has spread widely. Costs typically range from a few hundred to several thousand dollars, depending on the size of the room, the type of flooring on top, and the extent of the rot. After the repair, you can choose new flooring that suits your space.
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Call Now (386) 272-5697Frequently asked questions
Can a rotting subfloor be repaired without replacing it?
Small, isolated areas of rot can sometimes be repaired by drying the wood and applying a wood hardener or epoxy filler. However, if the subfloor has lost structural strength or mold has spread, replacement is usually safer. A pro can tell you whether a patch will hold or if a full section needs to go.
How long does it take for a subfloor to rot?
Rot can develop in as little as a few weeks if wood stays consistently wet, but it often takes months or years of moisture exposure. The speed depends on the type of wood, humidity levels, and whether the area has good airflow. You should address any water leak right away to slow the process.
Will insurance cover subfloor rot damage?
Policies vary, and your insurer decides what is covered. Sudden water damage from a burst pipe is more likely to be covered than gradual rot from a long-term leak. Check your policy and talk with your insurance company about your specific situation. They will let you know what applies to your claim.