Excessive moisture for whatever reason can have a devastating effect on timber.
Timber rot comes in many different forms and it is all fungi based. The fungi will strip the nutrients and water from the wood and cause the wood to dry, crack, weaken and often disintegrate. This can cause serious structual damage.
To eradcicate timber rot the source of mositure will first have to be removed from being in contact with the timber and then depending on how decayed the timber is and what type of rot, the timber will either dry out by it’s self, or it will have to be sprayed with a preservative, or be replaced.