How to Tell If You Have Dry Rot
Dry rot is a fungus that digests wood from the inside. By the time it is obvious from the street it has usually been working for years. Here is what to look for while it is still cheap to fix.
What to check from the ground
- Fascia boards behind the gutters that look darkened, swollen or wavy
- Paint that blisters or will not hold on the eaves, no matter how often it is redone
- Rafter tails — the exposed beam ends under the overhang — that look crumbly at the tip
- A roofline that dips or waves where it should be straight
- Gutters pulling away from the house, because the wood behind them is too soft to hold a screw
The screwdriver test
Press a screwdriver into the suspect wood with moderate pressure. Sound wood resists. Rotted wood takes the tip with almost no effort and comes away spongy or crumbly.
If it sinks in, the damage extends further than the spot you tested — rot spreads along the grain, and what you can reach from a ladder is usually the edge of it.
Where it hides
Under the roof covering, on the sheathing. In Sacramento County that is common enough to be expected: 37% of re-roof permits from 2023 to 2025 also involved sheathing, dry rot or structural work.
That is why it is normally discovered on tear-off day, and why an honest roofing quote prices it in advance instead of pretending it will not appear.
Common questions
Is dry rot actually dry?
No — the name is misleading. It needs moisture to start, and it leaves the wood dry, brittle and crumbling once it has consumed it. If wood is crumbling, water got there at some point even if it is dry today.
Does dry rot spread?
Yes. The fungus travels along the grain and can move into adjoining framing. It does not stop on its own once moisture is present, which is why patching the paint over it does nothing.