How to Repair a Termite-Damaged Subfloor

The subfloor is the layer of plywood or OSB that sits directly on top of your floor joists. Because it is horizontal and often stays moist if there are leaks, it is a prime target for termite activity.

Signs of Subfloor Damage

Subfloor damage is often hidden beneath carpet, tile, or hardwood. Signs include:

• Soft Spots: Areas of the floor that feel "spongy" or give way when stepped on.
• Cracked Tile: Movement in a damaged subfloor will often cause the grout and tiles above to crack.
• Squeaking: As the wood is hollowed out, it loses its ability to hold nails firmly, leading to floor noise.

The Repair Process

Repairing a subfloor almost always requires removing the finished flooring above it.

1. Assessment

Remove a section of the finished floor to see the extent of the damage. Termites often travel along the edges of the plywood where it meets the joists.

2. Removal

Cut out the damaged sections of plywood. It is best to cut back to the center of the nearest healthy floor joist to ensure the new piece has a solid support to rest on.

3. Joist Inspection

Once the subfloor is removed, inspect the tops of the floor joists. Termites that eat the subfloor have almost certainly been active in the joists as well.

4. Installation

Install new plywood of the same thickness as the original. Use construction adhesive and screws (rather than nails) to ensure a quiet, solid repair.