Direct answer: If you suspect termite damage in a subfloor, first figure out whether the termites are still active and how far the wood loss goes. Small, old damage can sometimes be repaired after treatment, but widespread softness, sagging, or support damage is a contractor-and-pest-pro job.
Most likely: The most common real-world pattern is hidden wood loss around a damp area, crawlspace, rim area, or plumbing leak where termites had easy access and moisture helped them along.
A subfloor can look fine on top and be hollow underneath. Termites usually leave a thin surface skin while eating the wood inside, so the floor may feel spongy, sound papery, or dip near a wall, toilet, tub, or exterior edge. Reality check: by the time you feel it underfoot, the damage is often bigger than the first soft spot. Common wrong move: treating this like a simple squeaky-floor repair and covering it up before checking the framing below.
Don’t start with: Do not start by patching over soft flooring, adding screws, or buying plywood before you know whether the infestation is active and whether joists or supports are involved.
One section gives a little when you step on it, often near an exterior wall, bathroom fixture, or kitchen sink area.
Start here: Start by checking whether the area is dry or damp and whether you can inspect the underside from the basement or crawlspace.
The finished floor may not be broken, but tapping or walking over it sounds thin or papery.
Start here: Look for hidden wood loss from below before assuming it is just loose flooring.
The floor drops toward a wall, beam line, or plumbing area, sometimes with trim gaps or cracked caulk nearby.
Start here: Treat this as possible structural damage, not just surface subfloor damage.
You see mud tubes, blistered wood, shed wings, or galleries in exposed wood under the room.
Start here: Separate active termite activity from old repaired damage before planning any wood replacement.
Mud tubes, fresh-looking galleries, live insects, or new damage around damp wood strongly point to termites still working.
Quick check: Inspect exposed wood from below with a flashlight. Look for pencil-width mud tubes, hollow wood, and areas that break open easily with light probing.
The wood may be scarred and weakened, but dry, dusty, and inactive with no fresh tubes or live insects.
Quick check: Break a small loose fragment from already damaged wood if available. Old damage is often dry and brittle, with no moist mud packing or live activity nearby.
Rot is common around toilets, tubs, doors, and plumbing leaks, and it can feel almost identical underfoot.
Quick check: Rot usually follows obvious water staining or chronic dampness and tends to be darker, stringier, or crumbly rather than packed with mud or layered galleries.
If the floor sags, walls above show movement, or multiple adjacent areas feel weak, the problem is often beyond the subfloor sheet itself.
Quick check: From below, sight along the joists and look for crushed wood fibers, deep insect channels, split bearing points, or temporary shimming from a past repair.
If termites are still active, replacing wood first just gives them fresh material and hides the real problem.
Next move: If you find active signs, stop repair planning and arrange termite treatment first. After treatment, the damaged area can be opened and repaired with a clear scope. If you find no active signs, keep going. You still need to separate old insect damage from rot and find out how far the weakness runs.
What to conclude: The first decision is not what wood to buy. It is whether you are dealing with a live pest problem or leftover damage.
These two problems overlap all the time, and the repair only lasts if you fix the right cause.
Next move: If you find a clear moisture source, fix that source before any subfloor repair. If termite signs are also present, both issues need attention. If the area is dry and the damage pattern still looks insect-made, move on to mapping the size of the weak section.
What to conclude: A lot of 'termite damage' turns out to be rot, or a mix of both. The floor repair is only the finish work after the source is handled.
The visible soft spot is usually smaller than the real damaged area, especially with termites.
Next move: If the weak area is small and the joists look solid, you may be looking at a localized subfloor repair after treatment and moisture correction. If the weakness keeps spreading, crosses several joist bays, or reaches supports, plan for a larger structural repair scope.
Homeowners can sometimes handle a small, dry, well-defined subfloor patch. Structural termite damage is a different level of work.
Next move: If it is truly localized, you can move ahead with opening the floor and replacing the damaged subfloor section after termite treatment and source correction. If it is structural or uncertain, the right next move is a pest pro plus a qualified contractor, not a cosmetic patch.
Once you know whether the damage is active, wet, local, or structural, the next move becomes pretty straightforward.
A good result: A solid floor with dry wood below and no new termite signs means the repair path was correct.
If not: If the floor still moves, the damage was broader than the first opening showed, or the support framing needs repair.
What to conclude: The job is done when the pests are handled, the moisture source is handled, and the floor is solid again—not when the soft spot is merely covered.
It depends on how far the damage goes. A small, dry, inactive area with solid joists can often be cut back to sound wood and patched. If joists, rim board, or supports are damaged, the repair is bigger and usually needs a contractor.
Termite damage often leaves hollowed galleries and a thin outer skin of wood, sometimes with mud packing. Rot usually follows a leak or damp area and feels more fibrous, punky, or crumbly. In real houses, you can have both at once.
No. The termites may be long gone, and you may just be feeling the leftover wood loss. But you should not assume that. Check for live insects, fresh mud tubes, or new debris before repairing the floor.
If you see active termite signs, call a pest control company first so the infestation is treated before the floor is closed up. If the floor is sagging or framing is damaged, line up a contractor as well.
That is usually the wrong move. Screws and overlay material do not restore eaten-away wood underneath, and they can hide active damage. You need to know whether the subfloor and framing below are still sound first.
Not usually the concrete itself. The concern is the wood sitting near or on the foundation, such as sill plates, rim areas, joists, and subfloor edges. That is why checking the framing near the foundation matters.