Dry Rot or Termites? How to Tell What You're Looking At
You pushed a screwdriver into a window sill and it sank in like it was cake. Or you pulled off a piece of trim and the wood behind it just fell apart. Now you're wondering: dry rot or termites?
It matters, because the fix is different. Rot is a water problem. Termites are a pest problem. Treat the wrong one and the damage keeps going.
The short answer: dry rot cracks wood into small cubes and turns it brown and crumbly, and it almost always sits where water gets in. Termites hollow wood out from the inside and leave tunnels plus either mud (subterranean termites) or tiny six-sided pellets (drywood termites). If the surface is cracked into squares, think rot. If the surface looks fine but the inside is tunneled, think termites.
Dry rot vs termite damage at a glance
What to check | Dry rot (fungus) | Drywood termites | Subterranean termites |
Surface | Cracked into small cubes, shrunken, darker brown | Often looks normal, with tiny round holes | Often looks normal, mud tubes nearby |
Inside the wood | Crumbles to powder when dry, spongy when wet | Smooth, clean tunnels and chambers | Tunnels that follow the grain, soft wood eaten out between the rings |
What's around it | Musty smell, white or gray fungal strands | Small piles of pellets like coarse sand | Mud tubes on foundations or walls |
Where it shows up | Sills, trim, fascia, deck boards, anywhere water sits | Attics, eaves, rafter tails, dry framing, furniture | Mudsills, crawlspace framing, wood near soil |
Needs moisture? | Yes | No | Yes, plus soil contact |
The screwdriver test
You can usually sort this out in a few minutes with a flat screwdriver and a flashlight.
Probe the edges, not the worst spot. Rotted wood gives way evenly, like pushing into cork. Termite-damaged wood often has a firm outer shell, then the tip suddenly drops into a hollow.
Pry up a sliver. Rot snaps short across the grain, almost like charcoal. Termite-damaged wood tends to peel apart in layers along the grain, with tunnels showing.
Look at what's on the tip. Brown powder points to rot. Dirt or a mud-like crust points to subterranean termites. Clean, empty tunnels point to drywood termites.
Look underneath. Little piles of pellets on the sill, floor, or attic insulation are the giveaway for drywood termites.
Find the water. If there's no leak, drip line, or soil contact anywhere near it, rot is unlikely and drywood termites move to the top of the list.
What does dry rot look like?
Dry rot isn't actually dry. It's a wood-eating fungus (a brown rot) that needs wet wood to get going. A study co-authored by the USDA Forest Products Laboratory found wood won't decay below about 20% moisture content and will above about 30%. It gets the name because the wood it leaves behind looks dry, shrunken, and brittle.
Signs of dry rot:
Cracks running across the grain that break the surface into little cubes
Wood that's darker brown and has shrunk or sunk below the paint line
Paint that's bubbling, cracking, or peeling in one area
Wood that crumbles to powder when you rub it between your fingers
A spongy feel when it's wet
A musty, mushroom smell
White or gray cottony strands, or fan shapes, on the surface or behind trim
What causes dry rot in wood is almost always water that keeps coming back. On Bay Area homes we see it most at window sills with failed caulk, deck ledgers without flashing, fascia under overflowing gutters, siding that sprinklers hit every morning, and crawlspaces with poor ventilation. Fog and winter rain don't help, especially on older houses with original trim.
What does termite damage look like on wood?
Two termites do most of the damage around here: the western drywood termite and the western subterranean termite. They leave very different evidence.
Drywood termites live entirely inside the wood and, according to UC Statewide IPM, don't need any soil contact. Look for:
Tiny kick-out holes, smaller than 2 mm across
Pellets that are hard, six-sided, and about the size of a grain of sand, piled up below those holes
Smooth, clean tunnels that cut across the grain
Swarmers or shed wings on window sills, usually summer through fall
Subterranean termites need moist soil, so they nest in the ground and travel up into the house. The UC Statewide IPM Program lists these as the main signs:
Mud tubes running from the soil up foundations, piers, or inside walls
Damage that follows the grain, leaving the harder growth rings behind like a layered honeycomb
Long hollow tunnels, sometimes with light-brown droppings inside, and wood that's thin and blistered at the surface
Swarms on clear days after a soaking rain, usually in spring or fall
How to identify termite damage when you can't see inside: tap the wood with the handle of the screwdriver. A hollow, papery sound over wood that looks fine on the surface is a strong sign of termites.
Can it be both?
Yes, and it happens a lot. Rot and subterranean termites both love wet wood, so a long-running leak can feed both at once. There's also a third player on the coast, the dampwood termite, which lives in wood that stays wet, often wood touching soil or under a leaking deck. Finding rot doesn't rule out termites. Whatever you find, fix the water.
What to do once you know
If it's dry rot: stop the water first. Then the damaged wood gets cut back to solid material and replaced, primed on all sides, and flashed or sealed so water can't get back in. Small, non-structural spots on trim can sometimes be consolidated with epoxy. Anything in a sill plate, joist, post, beam, or deck ledger needs a contractor, because that wood is carrying load. For real numbers, see our breakdown of dry rot repair cost in the Bay Area.
If it's termites: call a licensed pest control company first. We don't treat termites, and neither should a general contractor. Once the colony is handled, the damaged wood gets repaired or replaced. Do it in that order, or the new wood just becomes the next meal.
Bay Area homeowners: dry rot shows up on your termite report
If you're buying or selling a home in California, you'll probably see a Wood Destroying Pests and Organisms report, which most people call a termite report. California law sets what goes in it, including termites and fungus damage, which is how dry rot gets listed.
Findings are split into two parts:
Section 1: active infestation or infection, or damage it has already caused. These are the items buyers and lenders usually want cleared before closing.
Section 2: conditions likely to lead to a problem, like excess moisture, where no damage was found yet.
The pest company will usually bid the repairs on its own report, but you're free to get a bid from a licensed contractor for the wood repair work. If you've got a report in hand and aren't sure what the line items mean, book a construction consultation and we'll walk through it with you.
When to call a contractor
Call a pro if the damage is bigger than your hand, if it's in anything holding weight, if you find it in more than one spot, or if the wood sits on or near a foundation. Those are the cases where hidden damage tends to be worse than what you can see.
Pillar to Pillar Construction handles dry rot and structural repair across San Francisco and the Bay Area, from window sills and fascia to mudsills, posts, and deck framing. Owner Jerry Lyons is a licensed general contractor, CSLB #1137809. Call him at (415) 310-7678 or see some of our recent work.
FAQ
Is dry rot the same as wood rot?
Dry rot is one type of wood rot, caused by brown rot fungi. In the US, most people use "dry rot" for any rot they find in a house, and termite reports in California list it as fungus damage.
What does termite damage look like on sheetrock?
Look for pinholes, faint lines of dried mud, bubbling or peeling paint, and spots that sag or sound hollow when you tap them. Subterranean termites will eat the paper face of drywall on the way to the wood framing behind it.
How can you tell if termite damage is old?
Sweep up any pellets and check the spot again in a few days. New pellets mean an active drywood colony. For subterranean termites, break a small section out of a mud tube; if it's rebuilt within a few days, they're still active.
Does dry rot spread?
It keeps spreading as long as the wood stays wet. Dry the wood out and the fungus stops, but it can start again if water returns, which is why damaged wood gets removed instead of left in place.
What is Section 1 on a termite report?
Section 1 lists active termite infestation, fungus infection, or damage already done. Section 2 lists conditions that could lead to those problems but haven't yet.
Does homeowners insurance cover dry rot or termite damage?
Usually not. Most policies treat both as maintenance or gradual damage. Check your own policy, since a sudden covered event (like a burst pipe) can sometimes change the picture.
