These problems may be observed in both heated and unheated buildings, are more pronounced on edges and ends of boards and are also observed where water is held on the surface.
Porous paints are particularly vulnerable to moisture penetration.
Proper construction and maintenance will eliminate most exterior water problems. Ice dams occur in cold northern climates when snow on the upper warmer parts of a roof melts and runs downward. As the melted snow reaches the roof overhang which is not heated, it freezes once more. With repeated thawing and freezing on the roof more water moves to the roof edge and an ice dam begins to build up. The melted water may penetrate the roof and drain into the exterior walls, thus causing moisture and associated paint problems.