How to Tell If Termite Damage Is Structural

Cosmetic versus structural termite damage

The question that actually matters with termite damage is not how bad it looks. It is what the damaged wood does. Damage to trim, paneling, a window casing, or a baseboard is cosmetic: unpleasant, worth fixing, but nothing depends on it. Damage to anything carrying weight (beams, girders, joists, sill plates, posts, studs in bearing walls, headers over openings) is structural, and that is the kind that affects your home's safety and value. Two pieces of wood with identical damage can be a weekend fix or a shored structural repair depending entirely on their job.

Step one: figure out what the damaged wood is doing

Before judging how deep the damage goes, identify the piece. In a basement or crawl space, the large timber running the length of the house is usually the main beam or girder, carrying the floor joists that rest on it. The joists are the repeated members spanning from the foundation to that beam. The sill plate is the flat piece sitting on top of the foundation wall, with the joists or wall framing resting on it. Posts carry the beam down to footings. If the damage is in any of these, assume structural until proven otherwise. If it is in a trim board, a stair skirt, or a shelf, it probably is not.

Clues you can check yourself

• Press damaged wood with a screwdriver. If it crumbles or the tip sinks in easily, the wood has lost strength.
• Tap suspect framing. A hollow or papery sound means it has been eaten out inside.
• Note whether the damaged wood is holding something up: a floor, a wall, a beam, or a stair.
• Watch for movement. Sagging floors, sticking doors, and new cracks signal load problems.
• Look low. Sills and crawl space framing near grade are where structural damage starts.
• Check where damage meets support. Joist ends resting on a sill or beam carry concentrated load.

Step two: judge how much of the cross-section is gone

A piece of framing gets its strength from its full depth and width. Termite galleries running along the grain remove wood from inside, so a joist might look whole from below while a large part of its interior is gone. Damage near the middle of a span or at a bearing end matters more than damage in a lightly loaded spot. This is the part a homeowner cannot reliably judge from the surface, and it is where probing along the length of each member becomes necessary.

Why a probe beats a glance

Subterranean termites leave a thin shell of sound-looking wood over a hollowed core, so the surface routinely understates the damage. A visual inspection, including the WDI report done for a home sale, records what can be seen; it is not designed to measure how far damage runs inside a board. Our guide to reading a termite inspection report covers that limit in more detail. The only reliable way to know how far structural damage runs is to probe the framing along its length and follow the damage to its edges, which is part of every assessment we do.

Signs that point toward structural damage

• Damage in a sill plate, beam, girder, post, or joist rather than trim
• A floor above the damage that sags, bounces, or has changed over time
• Damage at the end of a joist where it bears on a sill or beam
• Gaps opening between the foundation and the framing above it
• Doors and windows nearby that have gone out of square

Signs that point toward cosmetic damage

• Damage limited to trim, casing, paneling, or a non-bearing piece
• Framing near the damage that is firm under a screwdriver along its length
• No movement, sag, or cracking in the floors and walls above
• Damage that stops cleanly where a probe meets sound wood

If it is structural, what is next

Once it is clear the damage is structural, the path is straightforward: confirm the colony is treated by a licensed pest control company, assess the full extent, and rebuild the weakened wood to code. Depending on what is found, that may mean joist and subfloor repair or beam and sill replacement, usually with a permit and inspection. We give you a free on-site assessment and a clear written price so you know exactly where you stand.

Common questions

Can I just fill termite damage with wood filler or epoxy?

On trim and non-structural wood, filler can be a reasonable cosmetic fix once the colony is treated. On load-bearing framing, filler does not restore the strength the termites removed, so damaged structural wood needs to be reinforced or replaced.

Is a little termite damage on a joist a big deal?

It depends where it is and how deep it goes. Shallow surface damage in a lightly loaded spot may be minor, while damage at a bearing end or hidden deep inside the joist can matter a lot. Probing tells you which.

Should I have an engineer look at it?

For major damage to beams, girders, or multiple bearing members, or where a municipality asks for design details, input from a structural engineer can be appropriate. Many routine sill and joist repairs are handled to code by a qualified contractor.

Can I stay in my home during a structural termite repair?

In many cases, yes, because the work is often done from the basement or crawl space with the structure shored. Larger repairs that open floors or bearing walls may affect parts of the house for a period, which your contractor should explain in the scope.