I recently inspected a basement wall in a ten year old home that was leaking. I was disappointed but not surprised to find out that all the effort was a result of the poor workmanship of the builder. In this case the wall was taken apart to find the source of the problem. From the outside it occurred to me that there may not have been any tar paper under the stucco but when the wall was opened up there was tar paper but it was installed improperly. As the title suggests the mistake was small but the under lapping of the tar paper cost this homeowner a lot of money. When the stucco got wet from the dripping water from the joint in the bottom belt strip (bottom trim of the siding) it soaked through to the tar paper as it is supposed to. The problem is that the water was then directed in against the OSB (instead of away from it) where it created mold and rot.
The same thing happened in the corner when the downspout was not properly extended out away from the home. The entire corner was beginning to rot. I have seen this in the advanced stages on older homes where the entire corner including the framing was compromised, thus causing the home to shift slightly, not to mention the mold growth. Its hard to imagine the damage that one small oversight by the builder/renovator could cause such a large problem, but it does albeit slowly over many years. The tools used by a good home inspector such as thermal imaging and a good quality moisture meter along with experience may help the home buyer identify this type of problem before they own the home and the problem.