When hiring a home inspector, buyers typically believe that stability of the foundation is the main focus of the inspection when, in reality, serious foundation problems are among the some of least common building defects. Problems with roofing material, due to aging, wear, or improper installation, are likely to be found in the majority of homes. This does not mean that most roofs require replacement, but rather that most could use some type of maintenance or repair. Unfortunately, you often can't tell if the roof still leaks unless you inspect on a rainy day. Some stains are merely the residual effects of roof problems that have been repaired, while others may be related to leaky plumbing.
Correction can be as simple as re-grading the exterior grounds or adding roof gutters.
Unfortunately, major drainage improvements are often warranted, requiring costly ground water systems such as french drains designed by geotechnical engineers. Such problems may result from errors at the time of construction but often are due to wiring that was added or altered by persons other than qualified electricians. If left unchecked, damage can be quite extensive. This is a red flag to most inspectors, because no one could possibly know the entire building code, let alone the average person without construction knowledge. Whenever an owner offers code assurance, problems are likely to be found.