What is Wood Rot? And what is the cause?
It is a form of Decay. And Fungus that digests moist wood, cause wood rot. And it is considered a serious concern.

What should you do?
The annual mission for the homeowner to check its sign. It is your investment, take care of it, please.
The best time, Summer or Spring.
Tools, Screwdriver with a Flashlight.

Best Solution:

Replacement, and Preventions.