Build Green: Wood Can Last for Centuries cites splashing rain as another source of moisture that can make wood decay. As an example of this, water flowing off the roof and splashing against the house may also wet wood siding enough to permit decay.
This problem frequently occurs where water flows from the roof onto a hard-surfaced patio, sidewalk, or entryway parallel to the home. Sometimes this problem is inadvertently increased through the use of diverters over the doorway such as an entry canopy. If the stream of water draining from the diverter flows or splashes against exterior woodwork, wood that otherwise could provide satisfactory service may decay.
Usually, this hazard can be prevented through careful design of house and entryway and through appropriate use of preservative-treated products at the time of construction. In existing houses, rain gutters should be installed with downspouts that direct water away from the house.