T1-11 is a very commonly used sheet product used as a structural sheathing and is also a final siding.  This product needs to be sealed by paint to ensure years of trouble-free use.  One area very often forgotten is the bottom edge.  This area is most susceptible to water falling from the eves and splashing off the ground.  Plywood products act like straws and will soak up, or wick, water vertically and can be seen from the inside of the building near the bottom plate.  This action can be stopped by simply painting the bottom edge.