Learning Center · Pier & Beam
Wood Rot vs Termite Damage Under a House
TWO KINDS OF DAMAGE, ONE CRAWL SPACE
ROT · FUNGUS ON WET WOOD
Works from the wet face inward, so the bad wood is the wood you can see. Dark cubes across the grain, or pale and stringy, and it stops once the water is gone.
TERMITES · INSECTS FROM INSIDE
Works from the inside out and leaves the surface looking sound. Hollow when tapped, layered galleries with the grain, mud tubes on the piers, frass below.
BOTH · ONE WET CRAWL SPACE
The water that rots a sill is the water that draws subterranean termites. Plenty of houses have the two of them in the same bay over the same leak.
Either way the wood gets repaired. Only one of the two also needs a pest treatment.
Rot and termite damage both turn crawl space lumber soft, and the way to tell them apart is where the damage started. Rot works from the outside in, so the wood you can see is the wood that failed. It darkens, cracks into cubes across the grain, and gives way evenly under a probe. Termites work from the inside out, so a board looks fine until you tap it, hear a hollow, and push a screwdriver through a thin shell into a honeycomb of tunnels. One is a fungus eating wet wood. The other is an insect colony eating your framing and living somewhere else.
What rot looks and feels like
Rot is a fungus, and it needs wood, air, and steady moisture. Take the water away and it stops. Brown rot eats the lighter material and leaves the wood dark, shrunken, and cracked into rough cubes across the grain, and once it dries it crumbles to powder between your fingers. That is the one people call dry rot, a poor name for something that only started because a board stayed wet. White rot bleaches the wood pale and leaves it spongy, pulling apart in fibers rather than cubes.
Either kind shows itself on the surface. The damage runs continuous from the wet face inward, the color is wrong, the smell is musty and earthy, and a sharp probe slides in and comes back with fibers on it. No tunnels, no pellets, no mud, and nothing alive in there.
Location tells you nearly as much as texture. Rot goes where water sits. The sill line where grade got built up against the wood, beam ends on damp piers, joists under a bathroom, and the subfloor over a weeping drain line.
What termite damage looks like
Termites leave the outside of a board alone on purpose. They eat the interior along the grain, following the softer spring wood, and what they leave is a stack of layered galleries separated by walls of wood left paper thin. Tap a run of framing with a screwdriver handle and a hollow note is the first real signal. Push the tip in and it punches through the shell into a void.
Subterranean termites are the common species in Central Texas, and they give you the best evidence. They nest in the soil and will not cross open air, so they build shelter tubes out of mud and saliva, roughly the width of a pencil, climbing piers, skirting, and foundation walls. A tube running up a pier to a beam is the clearest evidence a crawl space gives you, and their galleries are usually smeared with that same mud.
Drywood termites keep no soil connection and keep a tidier house. Their galleries are clean and free of mud, and they push their droppings out through small holes, so you find neat piles of hard pellets, called frass, on the dirt or on top of a pier below the damage. Carpenter ants tunnel to nest rather than to eat, leaving smooth galleries and shavings closer to coarse sawdust than pellets. In spring, swarmers leaving to start new colonies drop their wings along the sill line and in the corner webs.
The probe test that settles it
Bring a flashlight and a sharp screwdriver or awl, and hold the light low so raking light picks up texture. Work the members closest to the ground first, the sills, the beam ends, and the joists over anywhere that stays wet.
Tap before you probe. Sound wood rings solid, and hollow means something ate the middle out of it. Then probe, and watch how the wood gives. Rot yields evenly the whole way in and peels off in fibers or breaks into cubes. Termite damage resists for an instant, then gives all at once into a gallery. Fibers and crumbs on the tip are rot. Mud inside a tunnel, hard pellets, or a shell over hollow layers running with the grain is insects.
Then stop looking at the wood and look at the dirt and the masonry. Mud tubes on piers, skirting, or a foundation wall mean subterranean termites, whether the framing above them looks damaged or not.
Moisture is what put both of them there
The two share a cause, which is why homeowners keep finding them together. Rot fungus cannot start on wood that stays dry, and subterranean termites want damp wood for their own reasons, so they pass over dry lumber to reach a board that has been wet for years. Both end up in the same bay, over the same leak, along the same buried sill.
That is why correcting the water leads every crawl space scope we write. Grading, downspouts, drainage, and the leak under the floor come first, and the full toolbox is in crawl space moisture control. New lumber set into the same wet conditions ages the way the old lumber did, and a termite treatment over an uncorrected leak invites the next colony back to the same damp wood.
Which one changes the repair scope
The carpentry is largely the same either way. Sistered joists, replaced sill runs, beams spliced over a pier, all of it walked through member by member in floor joist and sill repair. What the call changes is how far the cut lines travel and who else has to work on the house.
Rot stops where the water stopped, so probe outward from the soft area until the wood is sound again and the boundary usually turns up near the stain line. Termite galleries follow the colony rather than the water, and they can run up a post, along a beam, and into framing that looks untouched from below. Sound wood gets probed a good distance past the last visible damage before anyone draws a line.
Neither one is automatically a pier job. Damaged wood is a wood problem, and the supports under it join the scope only when the floor elevations show a pier has actually moved. Where underpinning is warranted we install steel and hybrid piers at $600 to $1,000 each, those piers carry a lifetime transferable warranty, and a yearly performance follow-up inspection keeps eyes on the job afterward. The symptoms that send people under the house are listed in the signs a pier and beam foundation needs repair.
Who to call, and when a WDI report belongs in the file
Motmot repairs structure. We do not sell pest control, termite treatment, or bait systems, and we are not licensed to. When our ICC-certified inspectors find galleries, mud tubes, frass, or shed wings under your house, we photograph what we found, tell you which of the two it reads as, and tell you to call a licensed pest control operator before any carpentry goes in.
A wood destroying insect report, the WDI, is that operator's document rather than ours. A licensed pest inspector walks the crawl space and the perimeter and writes up evidence of active or previous infestation and any visible damage. A sale or a lender will ask for one, and it is worth having even when nobody asks, because it dates the finding and puts treatment and structural repair on the same timeline. Get the treatment scheduled so new lumber is not the first thing a surviving colony meets. The structural half of the work sits on our pier and beam foundation repair page.
If crawling under there yourself is not happening, that is a normal choice. What you get back from us is the call itself. Our ICC-certified inspectors tap and probe the suspect framing, photograph what is behind the soft spot, crumbling fiber or layered galleries packed with mud, and name the culprit so you know whether a licensed pest control operator gets the first call or the carpentry does. The lumber side of the work, walked member by member, lives in floor joist and sill repair. About a third of our inspections end with no repair needed, and the inspection is free.