A homeowner pushes a screwdriver into a deck post and it sinks in. The wood is
soft, dark, and crumbling. The first thought is almost always termites.
Often it is not. And the distinction matters, because the two problems have
different causes, different fixes, and different odds of coming back.
The short answer
Dry rot is a fungus that decays wood in the presence of moisture. Termite
damage is an insect eating galleries through it. Rot needs water; remove the
water source and it stops. Termites need to be treated. Both appear as Section 1
findings on a report, and both frequently show up in the same spot — because the
conditions that create one tend to attract the other.
What dry rot actually is
The name is misleading. Dry rot is not dry and it is not caused by dryness. It is
a wood-destroying fungus that requires sustained moisture to grow.
What it looks like:
- Wood that is darkened, soft, and crumbles into cube-shaped chunks
- A surface that may look sound while the material behind it has failed
- Sometimes visible fungal growth — white strands or a brownish mass
- A musty smell in enclosed spaces
Where it appears: anywhere water sits or repeats. Around shower pans and tubs.
Under windows with failed caulking. At deck ledgers. At the base of siding where
a sprinkler hits it. In a crawl space under a slow plumbing leak.
The pattern follows the water. If you trace the damage back, there is nearly
always a source.
What termite damage looks like
Termite damage follows the insect, not the water.
Drywood termites leave clean galleries running with and across the grain,
often with the pellet piles described in
our guide to identifying species.
The wood surface frequently stays intact while the interior is hollowed out.
Subterranean termites leave galleries packed with soil, and the damage tends
to follow the softer spring wood in the grain, leaving a layered appearance.
The quick field test: rot crumbles into cubes and is usually wet or was
recently. Termite damage leaves tunnels with defined walls. If you break open a
soft area and find channels, you are looking at insect work. If you find
disintegrated material, you are looking at fungus.
Why they travel together
This is the part that surprises people. A leak that causes rot also creates the
moisture that attracts subterranean termites. Wood already softened by fungus is
easier to attack. Wood-to-soil contact delivers both the moisture and the access
route.
So the honest answer to “is it rot or termites” is frequently “both, and the same
leak caused it.”
That is why a report lists them separately but treats the conditions together.
Correcting the infestation without fixing the water source leaves the underlying
problem running.
Why the repair is different
For rot: find and fix the water source first. Replacing the wood without
fixing the leak just gives the fungus new material. Then remove all affected
wood, well past the visible damage, and rebuild.
For termites: treat the infestation, then evaluate the structural damage. In
many cases the damage is cosmetic and the treatment is the whole job. In others,
framing members have lost enough section that they need replacement.
For both: correct the
conducive conditions
so the situation does not repeat.
There is a practical wrinkle worth knowing. Structural repair in California
requires a contractor’s license. A company that only holds a pest control
registration can treat the infestation but cannot legally rebuild the framing —
which means a second company, a second schedule, and two parties who each say the
other one’s scope caused the problem.
Companies holding both licenses can carry the job from report to finished repair.
It is worth asking which situation you are in before work starts.
What you can check yourself
- Probe suspect wood with a screwdriver. Note whether it crumbles or tunnels.
- Look for a water source above and behind any soft area.
- Check where wood meets soil around the perimeter — the most common
conducive condition in the region. - Look at the shower and tub surrounds, particularly on second floors, where
a slow pan leak can run for years before anything shows on the ceiling below.
And then stop. Probing feels productive, but every hole you open in painted
siding is another entry point for water. Find the extent, leave the demolition to
the report.
J&M Termite Control holds California Branch 3 registration #5223 for
inspection and treatment, and CSLB general building license #983001 for the
structural repair side. From Mountain View since 1973.
